The Importance of Trunk Muscle Strength for Balance ... - Springer Link

Sports Med (2013) 43:627–641 DOI 10.1007/s40279-013-0041-1

SYSTEMATIC REVIEW

The Importance of Trunk Muscle Strength for Balance, Functional Performance, and Fall Prevention in Seniors: A Systematic Review Urs Granacher • Albert Gollhofer • Tibor Hortoba´gyi Reto W. Kressig • Thomas Muehlbauer

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Published online: 9 April 2013 Ó Springer International Publishing Switzerland 2013

Abstract Background The aging process results in a number of functional (e.g., deficits in balance and strength/power performance), neural (e.g., loss of sensory/motor neurons), muscular (e.g., atrophy of type-II muscle fibers in particular), and bone-related (e.g., osteoporosis) deteriorations. Traditionally, balance and/or lower extremity resistance training were used to mitigate these age-related deficits. However, the effects of resistance training are limited and poorly translate into improvements in balance, functional tasks, activities of daily living, and fall rates. Thus, it is necessary to develop and design new intervention programs that are specifically tailored to counteract age-related weaknesses. Recent studies indicate that measures of trunk muscle strength (TMS) are associated with variables of static/dynamic balance, functional performance, and falls (i.e., occurrence, fear, rate, and/or risk of falls). Further, there is preliminary evidence in the literature that core strength training (CST) and Pilates exercise training (PET)

U. Granacher (&) T. Muehlbauer Department of Training and Movement Sciences, Cluster of Excellency in Cognition Sciences, University of Potsdam, Am Neuen Palais 10, Haus 12, 14469 Potsdam, Germany e-mail: [email protected] A. Gollhofer Institute of Sport and Sport Science, Albert-Ludwigs-University of Freiburg, Freiburg, Germany T. Hortoba´gyi Centre for Human Movement Sciences, University Medical Centre Groningen, Groningen, Netherlands R. W. Kressig Division of Acute Geriatrics, Basel University Hospital, Basel, Switzerland

have a positive influence on measures of strength, balance, functional performance, and falls in older adults. Objective The objectives of this systematic literature review are: (a) to report potential associations between TMS/trunk muscle composition and balance, functional performance, and falls in old adults, and (b) to describe and discuss the effects of CST/PET on measures of TMS, balance, functional performance, and falls in seniors. Data Sources A systematic approach was employed to capture all articles related to TMS/trunk muscle composition, balance, functional performance, and falls in seniors that were identified using the electronic databases PubMed and Web of Science (1972 to February 2013). Study Selection A systematic approach was used to evaluate the 582 articles identified for initial review. Crosssectional (i.e., relationship) or longitudinal (i.e., intervention) studies were included if they investigated TMS and an outcome-related measure of balance, functional performance, and/or falls. In total, 20 studies met the inclusionary criteria for review. Study Appraisal and Synthesis Methods Longitudinal studies were evaluated using the Physiotherapy Evidence Database (PEDro) scale. Effect sizes (ES) were calculated whenever possible. For ease of discussion, the 20 articles were separated into three groups [i.e., cross-sectional (n = 6), CST (n = 9), PET (n = 5)]. Results The cross-sectional studies reported small-tomedium correlations between TMS/trunk muscle composition and balance, functional performance, and falls in older adults. Further, CST and/or PET proved to be feasible exercise programs for seniors with high-adherence rates. Age-related deficits in measures of TMS, balance, functional performance, and falls can be mitigated by CST (mean strength gain = 30 %, mean effect size = 0.99; mean balance/functional performance gain = 23 %, mean

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ES = 0.88) and by PET (mean strength gain = 12 %, mean ES = 0.52; mean balance/functional performance gain = 18 %, mean ES = 0.71). Limitations Given that the mean PEDro quality score did not reach the predetermined cut-off of C6 for the intervention studies, there is a need for more high-quality studies to explicitly identify the relevance of CST and PET to the elderly population. Conclusions Core strength training and/or PET can be used as an adjunct or even alternative to traditional balance and/or resistance training programs for old adults. Further, CST and PET are easy to administer in a group setting or in individual fall preventive or rehabilitative intervention programs because little equipment and space is needed to perform such exercises.

1 Introduction The age structure of societies in Western industrialized countries is undergoing rapid reorganization, with large increases in the number of seniors and reductions in the numbers of young citizens in the population [1]. Thus, there is a need for an integrative research effort among the fields of geriatrics, exercise science, and physiotherapy to address age-related and cost-intensive health care problems (e.g., high prevalence of falls). During the last two to three decades, several studies have determined the effects of exercise modalities on fall prevention (for a review, see Gillespie et al. [2]). Traditionally, balance and lower extremity resistance training were used to counter agerelated impairments in the neuromuscular (e.g., loss of sensory and motor neurons; atrophy of type-II muscle fibers in particular) and skeletal (e.g., osteoporosis) systems, contributing to an increased risk of falling (for a review, see Granacher et al. [3]). However, although resistance training improves maximal voluntary strength, even in the most elderly, concomitant improvements in functional outcomes are limited because the benefits of strength do not transfer effectively to improvements in balance, functional tasks, or activities of daily living, or to rate/risk of falling (for a review, see Orr et al. [4]). More recently, the lay literature in particular has promoted the importance of core or trunk muscle strength (TMS) for the successful performance of sports-related and everyday activities. As a consequence, researchers—specifically those working in the field of athletic performance—became interested in the topic and established a general understanding of the core concept. Functionally, the core is a kinetic link that facilitates the transfer of torques and angular momenta between upper and lower extremities during the execution of whole-body movements as part of sports skills, occupational skills, fitness

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activities, and activities of daily living [5]. Anatomically, the core can be described as a muscular box with the abdominals in the front, paraspinals and glutes in the back, the diaphragm as the roof, and the pelvic floor and hip girdle musculature as the bottom [6]. Kibler et al. [7] argued that the core is especially important in everyday and sports activities because it provides proximal stability for distal mobility. In fact, Kim [8] demonstrated that 12 weeks of core strength training (CST) significantly enhanced trunk extensor strength, spinal mobility, and driver shot performance in healthy female professional golfers with a mean age of 23 ± 4 years. However, research regarding the importance of TMS was applied not only in an athletic context but also in a rehabilitative setting. It has been shown that decreased trunk muscle endurance is strongly associated with the occurrence of low back pain [9]. Further, clinical guidelines have established that CST is an effective means of treating chronic low back pain [10]. Given these findings from the fields of athletic performance and rehabilitation, researchers have been trying to translate these promising results to the geriatric population. It can be hypothesized that enhanced core strength/stability or a combination of the two may allow old adults to use their upper and lower extremities more effectively by optimizing trunk movements (i.e., the mechanical linkage between upper and lower extremities), and by increasing the effectiveness of corrective movements in precarious situations encountered in daily life. In fact, van der Burg et al. [11] observed high activity of trunk muscles during compensation for a trip suffered while walking in order to stabilize the trunk over the base of support. Further, there is evidence in the literature for motor control deficits of the trunk muscles in older adults. For example, the paraspinal reflex latencies of the multifidus and the erector spinae muscles were delayed during sudden upper limb loading in old (mean age: 63 ± 3 years) compared to young (mean age: 27 ± 3 years) adults [12]. Further, a poor ability to recruit trunk muscles (e.g., transversus abdominis) correlates with an inability to perform activities of daily living (e.g., rising from a chair, stair negotiation) [13]. Thus, exercises that have the potential to promote appropriate dorsal (e.g., multifidus, erector spinae) and ventral (e.g., transversus abdominis, internal obliques) muscle responses may improve performance of activities of daily living due to enhanced TMS and core stability. For example, CosioLima et al. [14] observed significant increases in muscle activity (i.e., rectus abdominis and erector spinae muscles) during trunk flexion/extension after 5 weeks of CST (e.g., performing sit-ups and back extension exercises). Therefore, the objectives of this systematic literature review are: (a) to report potential associations between TMS/trunk muscle composition and balance, functional

Core Strength and Balance Performance

performance, and falls (i.e., occurrence, fear, rate, and/or risk of falls) in older adults, and (b) to describe and discuss the effects of CST/PET on measures of TMS, balance, functional performance, and falls in seniors.

2 Methods 2.1 Search Strategy Two systematic literature reviews were conducted from 1972 up to February 2013: one for cross-sectional (i.e., association, relationship, correlation) and one for longitudinal (i.e., training, intervention, exercise, conditioning, Pilates method) studies. The primary search was performed in the PubMed database and a secondary search in the Web of Science database. When using the PubMed database, the following Medical Subject Headings (MeSH) terms were applied: ‘‘torso’’ OR ‘‘back’’ OR ‘‘abdomen’’ OR ‘‘pelvis’’ OR ‘‘thorax’’ AND ‘‘trunk muscle strength’’ OR ‘‘trunk muscle composition’’ AND ‘‘balance’’ OR ‘‘functional performance’’ OR ‘‘falls’’ AND ‘‘association’’ OR ‘‘relationship’’ OR ‘‘correlation’’ (i.e., literature search for crosssectional studies)/‘‘training’’ OR ‘‘intervention’’ OR ‘‘exercise’’ OR ‘‘conditioning’’ OR ‘‘Pilates method’’ (i.e., literature search for longitudinal studies). The search was limited based on text availability (i.e., full text available), publication dates (i.e., last 40 years), species (i.e., humans), article types (i.e., journal article; clinical trial; randomized controlled trial), language (i.e., English) and ages (i.e., C60 years). The Web of Science search used the same terms and limits as mentioned before. Additionally, we searched for the terms ‘‘core strength’’ AND ‘‘older’’ in relevant journals within the sections gerontology/geriatric medicine (e.g., Age and Ageing; Gerontology; Journal of the American Geriatrics Society; Journals of Gerontology) and conditioning (e.g., Journal of Sports Science and Medicine; Journal of Strength and Conditioning Research). Duplicates between searches were removed. Results of the search procedures are summarized in Fig. 1. 2.2 Selection Criteria Studies were included in the review if they: (a) were published in peer-reviewed journals; (b) had study participants who were aged C60 years (except otherwise stated due to a limited amount of studies available); and (c) had incorporated at least one strength, balance, functional performance or fall-related outcome measure. Studies were excluded if they: (a) did not meet the minimum requirements of an experimental study design (e.g., case reports); (b) did not meet the minimum requirements regarding

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training design (e.g., lack of information on volume, frequency, and/or intensity of training); and (c) were not written in English. Based on the inclusion and exclusion criteria, two independent reviewers (UG, TM) screened citations of potentially relevant publications. If the citation showed any potential relevance, it was screened at the abstract level. When abstracts indicated potential inclusion, full text articles were reviewed for inclusion. A third-party consensus meeting was held with RWK if the two reviewers (UG, TM) were not able to reach agreement upon inclusion of an article. 2.3 Quality Assessment and Effect Size Calculation Given that there is no consensus regarding reliable and valid instruments for the assessment of methodological quality of cross-sectional studies [15], neither rating nor weighting of studies was conducted. However, different aspects of methodological quality (e.g., participant characteristics, TMS/trunk muscle composition tests, balance and functional performance tests) were extracted from the articles and are reported in the ‘‘Results’’ section. For intervention studies, two independent reviewers (UG, TM) performed quality assessments of the included studies, and disagreements were resolved during a consensus meeting or rating by a third assessor (RWK). Initially, methodological quality was assessed using the Physiotherapy Evidence Database (PEDro) scale [16], an 11-item scale that includes the 3-item Jadad scale [17] and the 9-item Delphi list [18]. The PEDro scale rates randomized controlled trials from 0 to 10, with 6 representing the cut-off score for high-quality studies [16]. One question is used to establish external validity and is not included in the score. Maher et al. [16] demonstrated fair-to-good inter-rater reliability with an intra-class correlation coefficient of 0.68 when using consensus ratings generated by 2 or 3 raters. A meta-analysis of the intervention studies was not feasible due to inherent parameter heterogeneity in CST and PET studies. In addition, effect sizes (ES) of study-specific outcome parameters were calculated according to the following formulae: ES = (mean post value intervention group - mean post value control group)/root mean [(post standard deviation squared intervention group ? post standard deviation squared control group)/2] (for between-subjects studies) or ES = (mean pre value - mean post value)/SD pre value (for within-subjects studies). The ES is a measure of the effectiveness of a treatment, and it helps to determine whether a statistically significant difference is a difference of practical concern. ES values of 0.20 indicate small, of 0.50 indicate medium, and of 0.80 indicate large effects [19].

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Fig. 1 Flowchart illustrating the different phases of the search and selection of the cross-sectional and longitudinal studies

3 Results Figure 1 displays a flow chart containing potentially relevant journal articles. A total of 582 studies were identified from the literature searches (i.e., n = 125 cross-sectional studies; n = 457 longitudinal studies). Twenty-six duplicates were removed. Three-hundred fifty-four studies were excluded on the basis of title or abstract. Of the remaining 202 studies, 182 studies were excluded on the basis of eligibility criteria. Finally, 6 cross-sectional studies (Table 1) and 14 longitudinal studies (Table 2 and 3) met the inclusion criteria for the present review. Of note, the full text of one longitudinal study was not accessible through the journal’s website or by directly contacting the authors of the article via email [20], which is why this study was excluded. 3.1 Overall Findings 3.1.1 Cross-sectional Studies All included cross-sectional studies reported small-tomedium, mostly statistically significant, correlations between variables of TMS/trunk muscle composition,

balance, functional performance, and falls in older adults (Table 1). Further, it seems that the relationship between measures of TMS and occurrence of falls becomes more prevalent with increasing age. 3.1.2 Longitudinal Studies All included studies that investigated the effects of CST reported significant improvements in TMS, balance, functional performance, and/or falls (i.e., fear of falling, fall efficacy) in healthy older subjects and in seniors with kyphosis (mean strength gain = 30 %, mean ES = 0.99; mean balance/functional performance gain = 23 %, mean ES = 0.88) (Table 2). Following PET, improvements in different measures of TMS, balance, functional performance, and falls were reported for healthy older adults (mean strength gain = 12 %, mean ES = 0.52; mean balance/functional performance gain = 18 %, mean ES = 0.71) (Table 3). However, most of the CST and PET studies did not reach the predetermined cut-off of C6 on the PEDro scale, indicating that the overall study quality is rather weak. Thus, future studies should specifically focus on the

1,194; F (621), M (573); 70–79; patients with low back pain

70; F (47), M (23); 65–94; mobilitylimited, community-dwelling

92; F (69), M (23); 60–92; healthy, fallers and non-fallers

Hicks et al. [36]

Suri et al. [38]

Kasukawa et al. [39]

COG displacement during standing with open eyes; number of falls within the past year

BBS; postural sway during one-legged stance; SPPB (e.g., tandem stance, gait speed)

Health ABC PPB (e.g., usual and narrow walk) at two clinic visits separated by 3 years

Health ABC PPB (e.g., usual and narrow walk); chair-stand test

COG displacement during two-legged standing with open eyes on firm ground; number of falls within the past 5 years

COF speed during standing with opened/ closed eyes; 10-m walking speed

Balance/functional performance test

Significant (p = 0.0052) relation between MIS of the trunk extensors and the presence of falls

Strength vs. balance: small to medium association; r2 B 17 %; strength vs. functional performance: small association; r2 B 14 %

Trunk muscle area vs. functional performance: small association; r2 \ 1 %; trunk muscle attenuation vs. functional performance: small association; r2 \ 12 %

Trunk muscle area vs. functional performance: small association; r2 \ 1 %; trunk muscle attenuation vs. functional performance: small association; r2 \ 13 %

Strength vs. balance: small association; r2 B 4 %; strength vs. falls: small association; r2 \ 1 %

Strength vs. balance: small-to-medium association; r2 B 18 %

Correlationa

a

Correlations are reported along with the proportion of variance in common (i.e., r2 multiplied by 100)

1RM one-repetition maximum, BBS Berg balance scale, COF center of force, COG center of gravity, F female, Health ABC PPB health, aging, and body composition study physical performance battery, M male, MIS maximal isometric strength, SPPB short physical performance battery

MIS of the trunk extensors

MIS of the trunk extensors/ flexors; trunk extension/ flexion endurance; leg press 1RM

Trunk muscle area/ attenuation

Trunk muscle area/ attenuation

1,527; F (788), M (739); 70–79; patients with low back pain

Hicks et al. [37]

MIS of the trunk extensors

MIS of the trunk extensors/ flexors

323; F; 75–80; community-dwelling

SakariRantala et al. [51]

Trunk muscle strength/ composition test/measure

Pfeifer 237; F; 63 ± 7; patients with osteoporosis et al. [35]

No. of subjects; sex; age (years) [mean ± SD or range]; characteristic

Study

Table 1 Studies (n = 6) examining the associations between trunk muscle strength/composition and balance, functional performance, and falls in older adults

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MIS trunk extensors (: 38 %; p \ 0.001; ES = 1.17)

MIS of the trunk extensors (: 60 %; p \ 0.001; ES = 1.42)

Spinal proprioceptive extension exercise dynamic program with a spinal weighted kyphoorthosis; 4 weeks; daily homebased; 20 min each session Trunk stabilization exercises with handheld dumbbells, free weights, Thera-bands; 12 weeks; 29/week; 50 min each session

25; F; INT (12), CON (13); [60; osteoporotic-kyphotic patients, healthy, physically active, communitydwelling

21; F; INT (21), CON (0); 66–80; patients with thoracic kyphosis, community-dwelling

90; INT 1 (30), INT 2 (30), CON (30); 64 ± 4; healthy

Sinaki et al. [29]

Katzman et al. [31]

Hosseini et al. [22]

Core stabilization training (i.e., INT 1) with semi-sit ups, situps with rotation, lateral bridge, prone bridge vs. strength training (i.e., INT 2) with squats, leg-press, deadlift, situps, knee flexion etc.; 6 weeks; 39/week; 60 min each session

INT 1: bench press 1RM (: 14 %; p [ 0.05; ES = 1.25); leg press 1RM (: 10 %; p [ 0.05; ES = 1.54); INT 2: bench press 1RM (: 36 %; p \ 0.05; ES = 2.44); leg press 1RM (: 33 %; p \ 0.05; ES = 5.05)

3

4

5

SOT (: 15 %; p = 0.003; ES = 0.85); gait speed while walking 10 m (: 7 %; p = 0.02; ES = 0.51); FES (; 58 %; p \ 0.001; ES = 1.37) SOT (: 3 %; p [ 0.05; ES = 0.25); COP displacement during two-legged stance with eyes closed (; 67 %; p [ 0.05; ES = 1.43); dynamic leaning task (; 1 %; p [ 0.05; ES = 0.10); gait speed while walking 7.5 m (: 4 %; p = 0.06; ES = 0.28); mPPT (: 7 %; p \ 0.001; ES = 0.77) INT 1: Y-balance test (: 46 %; p \ 0.001; ES = 2.37); DGI (: 42 %; p = 0.001; ES = 2.98); INT 2: Y-balance test (: 31 %; p \ 0.001; ES = 1.61); DGI (: 14 %; p [ 0.05; ES = 0.15)

3

FRT forward (: 45 %; p \ 0.01; ES = 1.34); FRT right (: 22 %; p \ 0.01; ES = 0.66); FRT left (: 43 %; p \ 0.01; ES = 1.39)

MIS of the trunk extensors (: 33 %; p \ 0.01; ES = 1.12)/ flexors (: 36 %; p \ 0.01; ES = 1.03)

Core strengthening program with the 6-second abs machine; 4 weeks; 29/week supervised ? 19/week homebased; 20 min each session

13; F (12), M (1); INT (13), CON (0); 61–82; healthy

5

PEDro score

One-legged standing time (: 22 %; p = 0.05; ES = 0.58); tandem walk (: 57 %; p = 0.52; ES = 1.39); FRT forward (: 20 %; p = 0.035; ES = 0.18); sit-and-reach test (: 43 %; p = 0.241; ES = 0.14); Reedco posture test (: 18 %; p = 0.002; ES = 0.39); fear of falling (; 11 %; p = 0.21; ES = 0.63)

Balance/functional performance gain

Chair rise test (: 21 %; p = 0.051; ES = 0.04), shelftask (: 49 %; p = 0.013; ES = 0.08)

Petrofsky et al. [30]

Trunk stabilization exercises with stability balls and hand weights; 10 weeks, 29/week; 45 min each session


Strength gain

Nichols et al. [24]

Training type, duration/frequency of training, session duration, training contents/equipment

No. of subjects; sex; group; age (years) [mean ± SD or range; characteristic

Study

Table 2 Studies (n = 9) examining the impact of core strength training (CST) on balance, functional performance, and falls in older adults

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78; F; INT (38), CON (40); 65; healthy, untrained

32; F (17), M (15); INT (16), CON (16); 63–80; healthy, physically active, community-dwelling

24; F (16), M (8); INT (12), CON (12); 65–85; healthy, community-dwelling

Kang et al. [23]

Seo et al. [28]

Granacher et al. [21]

Kahle and Tevald [34]

23 % (ES = 0.88)

30 % (ES = 0.99)

Means

6

FRT (: 5 %; p = 0.006; ES = 1.30); SEBT (: 11–20 %; p \ 0.001; ES = 1.90–3.10)

Curl-up test (: 8 %; p \ 0.001; ES = 4.40)

Core strengthening exercise program with bridging, reclining curl, curl-up, crunch, lower trunk rotation, straight leg rise, seated marching; 6 weeks; 39/week; 20–35 min each session

Sit-to-stand test (: 9 %; p \ 0.05; ES = 0.20); arm curl test (: 3 %; p \ 0.01; ES = 0.18)

8

Core instability strength training program with frontal, dorsal, rotational, and lateral core exercises with and without unstable training devices (e.g., balance pad, Swiss ball); 9 weeks; 29/week; 60 min each session

Swiss ball exercise program with bridging on the ball, hip adduction, sit up on the ball, back extension on the ball, bounce on the ball, pelvic rotation on the ball, knee extension on the ball, side bridging; 12 weeks; 29/week; 50 min each session

Stride velocity (: 9 %; p \ 0.05; ES = 0.44); stride velocity CV (: 31 %; p \ 0.05; ES = 0.41); FRT forward (: 20 %; p \ 0.01; ES = 0.59); TUG (; 4 %; p \ 0.05; ES = 0.39)

3

PEDro score

MIS of the trunk extensors (: 21 %; p \ 0.001; ES = 0.73)/ flexors (: 34 %; p \ 0.001; ES = 0.88); MIS of the lateral trunk flexors left (: 53 %; p = 0.001; ES = 0.69)/right (: 48 %; p \ 0.001; ES = 1.02); MIS of the trunk rotators right (: 38 %; p [ 0.05; ES = 0.23)/ left (: 42 %; p \ 0.001; ES = 0.80)

BBS (: 6 %; p = 0.01; ES = 0.20); weight support (: 11 %; p \ 0.05; ES = 0.86); stability (: 27 %; p \ 0.05; ES = 0.44)


3

NT

Strength gain

One-legged standing time (: 10 %; p \ 0.01; ES = 0.09); TUG (; 9 %; p \ 0.05; ES = 0.66); sit-and-reach test (: 24 %; p \ 0.001; ES = 0.52); back scratch test (: 36 %; p \ 0.05; ES = 0.39)

Core strengthening exercise program with of exercises in the bridging and crawling position; 8 weeks; 30 min each session


1RM one-repetition maximum, abs 6-second abdominals (abs) machine, BBS Berg balance scale, CON control group, COP center of pressure, CV coefficient of variation, DGI dynamic gait index, ES effect size, F female, FES fall efficacy scale, FRT functional reach test, INT intervention group, M male, mPPT modified physical performance test, MIS maximal isometric strength, NT not tested, PEDro Physiotherapy Evidence Database (i.e., signifies the methodological quality of clinical trials on a scale between 0 to a maximal score of 10), SEBT star excursion balance test, SOT sensory organization test, TUG timed-up-and-go test, :/; increase/decrease in percentage change (e.g., from pre- to post-testing)

No. of subjects; sex; group; age (years) [mean ± SD or range; characteristic

Study

Table 2 continued

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52; F; INT (27), CON (25); 60–78; healthy, sedentary

60; F; INT (30), CON (30); C65; healthy, sedentary

Rodrigues et al. [27]

Irez et al. [26]

9; F (8), M (1); INT (9), CON (0); 60–76; healthy, communitydwelling

NT

12 % (ES = 0.52)

Means

MIS of the knee extensors (: 3 %; p [ 0.05; ES = N/A); MIS of the ankle dorsiflexors (: 4 %; p [ 0.05; ES = N/ A)

MIS of the hip muscles (: 40 %; p \ 0.05; ES = 0.99)

NT

Sit-to-stand test (: 1 %; p [ 0.05; ES = 0.05)

Strength gain

Training included abdominal bracing and pelvic tilt exercises, a Swiss ball and wobble boards were used to enhance core stability; 8 weeks; 19/week; 60 min each session

Training consisted of standing and mat exercises followed by a circuit style session of Pilates reformer and mat based exercises; 5 weeks; 29/week supervised ? 19/week home-based; 60 min each session

Pilates exercises were performed using Thera-bands, exercise balls; 12 weeks; 39/ week; 60 min each session

Pilates exercises were performed using the Bobath ball, the cadillac, the wall unit, the combo chair, reformer devices; 8 weeks; 29/week; 60 min each session

Exercises were chosen to incorporate dimensions of balance, strength and coordination using the reformer leg press, Thera-bands, Swiss balls; 8 wk; 29/week; 60 min each session


18 % (ES = 0.71)

COP displacement during two-legged stance (; 2 %; p [ 0.05; ES = 0.56); fall risk index during stance perturbations (; 2 %; p = 0.09; ES = 0.65); gait speed (: 27 %; p \ 0.05; ES = 1.27), step length (: 24 %; p \ 0.05; ES = 0.83), gait variability (; 55 %; p [ 0.05; ES = 0.75) during walking on a treadmill

COP displacement during two-legged stance on foam ground with eyes open (; 17 %; p = 0.001; ES = 0.46)/closed (; 22 %; p \ 0.001; ES = 0.72); 4-square step test (; 7 %; p = 0.001; ES = 0.44); TUG (; 7 %; p \ 0.001; ES = 0.34)

Two-legged stance on a platform that is free to move (; 18 %; p \ 0.05; ES = 0.99); sit-andreach test (: 25 %; p \ 0.05; ES = 0.93); number of falls (; 80 %; p \ 0.01; ES = 0.99)

Tinetti test (: 4 %; p = 0.009; ES = 1.27); test of functional autonomy (e.g., 10-m walk etc.) (; 9 %; p \ 0.05; ES = 0.49)

Postural sway during two-legged stance with eyes open/closed on firm (; 2 %; p [ 0.05; ES = 0.24)/foam (; 27 %; p \ 0.05; ES = 0.99) surface; maximal balance range test (: 8–12 %; p \ 0.05; ES = 0.65–0.69); 4-stage balance test (; 1 %; p [ 0.05; ES = 0.38); TUG (; 7 %; p \ 0.05; ES = 0.56)


3

9

5

4

5

PEDro score

CON control group, COP center of pressure, ES effect size, F female, INT intervention group, M male, MIS maximal isometric strength, N/A not available, NT not tested, PEDro Physiotherapy Evidence Database (i.e., signifies the methodological quality of clinical trials on a scale between 0 to a maximal score of 10), TUG timed-up-and-go test, :/; increase/decrease in percentage change (e.g., from pre- to post-testing)

Newell et al. [33]

32; F (25), M (7); INT (14), CON (13); 67 ± 7; healthy, communitydwelling

8; F (4), M (4); INT (8), CON (0); 66–71; healthy, communitydwelling

Kaesler et al. [32]

Bird et al. [25]

No. of subjects; sex; group; age (years) [mean ± SD or range]; characteristic

Study

Table 3 Studies (n = 5) examining the impact of Pilates exercise training (PET) on balance, functional performance, and falls in older adults

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methodological quality of the applied CST and PET programs for the elderly population. 3.2 Study Characteristics 3.2.1 Study Design Six cross-sectional studies [i.e., relationship between TMS, trunk muscle area/attenuation (i.e., higher fat infiltration) and balance/functional performance/occurrence of falls in older adults] were eligible for inclusion in this systematic review. Fourteen longitudinal studies (i.e., effects of CST/ PET on measures of TMS, balance, functional performance, and fall rate/risk in seniors) were found and included in this manuscript. Of the 14 longitudinal studies, 9 studies investigated the effects of CST on TMS, balance, functional performance, and fall rate/risk, and 5 studies examined the impact of PET on these variables. Further, 8 out of the 14 longitudinal studies were unblinded randomized controlled trials [21–27]. Two studies were based on convenient samples [28, 29]. Four studies did not include a control group [30–33]. 3.2.2 Quality Assessment and Effect Size Calculation Quality assessment (i.e., PEDro scores) is presented in Tables 2 and 3 for the respective longitudinal studies. The mean quality score for the 14 included longitudinal studies amounted to 4.5 ± 1.6 (range 3–8) and 5.2 ± 2.3 (range 3–9) for CST and PET, respectively. The predetermined cutoff of C6 [16] was reached by three studies [21, 25, 34]. All other studies remained below this quality marker. Thus, the included longitudinal studies were considered to be of rather low quality. 3.2.3 Participant Characteristics A total of 3,427 and 524 subjects participated in the cross-sectional and the longitudinal studies, respectively. Most studies examined healthy community-dwelling older adults (cross-sectional studies: n = 3,357 subjects; longitudinal studies: n = 478 subjects) [21–26, 28, 32, 33]. The six cross-sectional studies comprised old adults who suffered from chronic diseases (e.g., osteoporosis, back pain) [35–37] or mobility impairments (e.g., had a history of falls) [38, 39]. Two longitudinal studies examined patients with chronic diseases (e.g., osteoporosis; thoracic kyphosis) (n = 46), which were also eligible for inclusion in this review [29, 31]. The age range of all participants amounted to 60–90 years. One cross-sectional study [35] and five longitudinal studies contained women only [26–29, 31].

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3.2.4 Intervention Characteristics Intervention programs of studies that were eligible for review comprised CST on stable and unstable surfaces and PET. Adherence rates during training were inconsistently reported and ranged between 84–100 % for CST [21, 24, 30, 31] and between 80–92 % for PET [25, 26, 32]. Interventions were conducted in a gym [24], in a senior center/residential house [26, 30], in an outpatient medical center [21, 31], in a private clinic [27], and at home [29, 30, 34]. CST was supervised by an expert on CST [21], by a physical therapist [31], or by trained instructors [24]. None of the other CST studies reported information on supervision of training. All PET studies were either supervised by certified Pilates instructors or by physiotherapists. In general, trunk muscle exercises were conducted in supine, prone, quadruped, and side-lying positions during CST and PET using unstable training devices (e.g., wobble board, balance pad, Swiss ball) [21, 24, 26–28, 32, 33] and resistive training devices [e.g., free/hand weights, dumbbells, 6-second abdominals (abs) machine, Thera-band, Pilates ring, reformer devices, combo chair, Cadillac, wall unit] (Fig. 2a, b) [24–27, 30–32]. More detailed information regarding training volume, training frequency, training contents, and training equipment are reported in Tables 2 and 3 for CST and PET, respectively. Progression during training was erratically described for both CST and PET. In CST, progression during training was achieved by modulating lever lengths [21, 24], range of motion [21], movement velocity (i.e., isometric, dynamic) [21], movement complexity (i.e., single/multi-joint movements) [24], level of stability/instability [21, 24], and by increasing training intensity [i.e., percentage of 1 repetition maximum (RM), workload, color/resistance of Thera-bands, Borg scale] [22, 28, 30] and training volume (i.e., number of sets/repetitions) [28, 31]. In PET, progression during training was realized by increasing the training volume (e.g., number of repetitions) [25], training intensity (e.g., training load, color/resistance of Thera-bands) [25, 26, 32], and level of stability/instability [26, 32, 33]. Control group activities varied across the CST/PET studies and included no treatment (i.e., usual daily activity with no increase in physical activity levels) [21–23, 26–29], waitlist for an exercise program upon completion of the study [25], and an alternative exercise program (i.e., stretching exercises) [24]. Finally, no longitudinal study reported training-related adverse events.

4 Discussion This is the first systematic review to examine potential associations between TMS/trunk muscle composition and

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Fig. 2a–b Participant performing a core strength exercise (a) and a Pilates exercise (b) using the Pilates ring

balance, functional performance, and falls in older adults, and to report the effects of CST/PET on measures of TMS, balance, functional performance, and falls in older adults. 4.1 Associations Between Trunk Muscle Strength (TMS), Balance, Functional Performance, and Falls in Older Adults Age-related mobility limitations and deteriorations in balance and functional performance have primarily been attributed to neuromuscular dysfunctions of the lower limbs [40]. As a consequence, these age-related lower extremity impairments are usually the target of intervention studies for the treatment of mobility, balance problems, and fall rate/risk [41]. More recently, it has been proposed that core stability may play a role in sports-related movements and/or activities of daily living that involve a dynamic component of forward motion in the sagittal plane, because the trunk extensors are necessary to stabilize the trunk above a relatively small base of support [7, 42]. Of note, this stabilizing function of the trunk extensors could be of

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particular importance for balance and mobility in older adults given that this age group often suffers from flexed (i.e., kyphotic) posture. In fact, kyphotic changes of the spine have previously been associated with poor balance and mobility in women aged 70–93 years [43] and in men with a mean age of 73 ± 7 years [44]. Further, Kasukawa et al. [39] observed a significantly larger angle of spinal kyphosis and spinal inclination in elderly fallers (mean age 77 ± 6 years) as compared to non-fallers (mean age 73 ± 8 years). There is also evidence from rehabilitation that trunk position significantly affects muscle forces distally in the leg, especially in the hamstrings, which are critical to trunk stabilization and balance recovery [45]. Building on these preliminary findings from the literature, this review systematically examined the associations between TMS/trunk muscle composition and balance, functional performance, and falls in older adults. In general, all included cross-sectional studies reported small-tomedium, mostly statistically significant, correlations between variables of TMS/trunk muscle composition, balance, functional performance, and falls in seniors (Table 1). Specifically, Suri et al. [38] set out to determine if there was an association between trunk muscle properties, mobility, and balance performance in mobility-limited community-dwelling old adults aged 65–94 years. The authors observed a small but significant correlation for maximal trunk extensor strength with one-legged balance performance (r = 0.30, p \ 0.05, r2 = 9 %). Further, trunk extension endurance was moderately correlated with the short physical performance battery (r = 0.37, p \ 0.05, r2 = 14 %) and the Berg balance scale (r = 0.41, p \ 0.05, r2 = 17 %). Pfeifer et al. [35] extended the findings of Suri and colleagues [38] to elderly women (mean age 63 ± 7 years) with osteoporosis. Maximal isometric back extensor strength was significantly associated with postural sway during quiet standing (r = -0.21, p \ 0.001, r2 = 4 %) and limitations in everyday life (r = -0.34, p \ 0.001, r2 = 10 %). However, no significant correlations were found between maximal isometric back extensor strength and number of falls during the previous 5 years (r = -0.07, p [ 0.05, r2 \ 1 %). In contrast to this finding, Kasukawa et al. [39] revealed that maximal isometric back extensor strength was significantly correlated with occurrence of falls (r = -0.34, p \ 0.01, r2 = 12 %) in elderly men and women with a mean age of 77 ± 7 years and a history of falls. This discrepancy in findings between the studies of Pfeifer et al. [35] and Kasukawa et al. [39] could be explained by marked differences in age between the study populations. In fact, these age differences are mirrored in lower maximal back extensor strength levels in the study of Kasukawa et al. [39] (i.e., 90 N, measured prone) as compared to that of Pfeifer et al. [35] (i.e., 374 N, measured while sitting).


Nevertheless, it could be hypothesized that the relationship between measures of TMS and occurrence of falls becomes more prevalent with increasing age. In cross-sectional (i.e., one clinic visit) and longitudinal (i.e., two clinic visits separated by 3 years) approaches, Hicks et al. [36, 37] investigated associations between trunk muscle composition (i.e., muscle area/attenuation of the abdominal, paraspinal, and thigh muscles) using computed tomography and physical performance using the Health ABC physical performance battery in a cohort of well-functioning men and women aged 70–79 years. In the cross-sectional study, Hicks et al. [37] found that trunk muscle attenuation (i.e., higher fat infiltration) but not trunk muscle area is significantly associated with performance in the Health ABC battery (r = 0.36, p \ 0.001) and the chair stand test (r = 0.24, p \ 0.001). Notably, average thigh muscle attenuation explained 6 % of the variance in physical function as compared to the 13 % explained by trunk muscle attenuation. Thus, the properties of trunk muscles appear to be more important for physical performance in older adults than the characteristics of the thigh muscles [37]. In the longitudinal study, Hicks et al. [36] showed significant positive associations between trunk muscle attenuation and physical function 3 years after the baseline assessment of the same cohort (r = 0.35, p \ 0.01). Trunk muscle attenuation contributed approximately 12 % to the explained variance in physical performance. It is of interest to note that the relationship between lower levels of trunk muscle attenuation and lower physical performance capacity was independent of thigh muscle composition [36]. In summary, these findings suggest that there is a low but significant relationship between TMS/trunk muscle attenuation and balance, functional performance, and falls in seniors. It appears that the importance of the trunk muscles (i.e., trunk muscle attenuation) for balance and mobility in older adults has been underestimated or perhaps overlooked. These results have implications for the promotion of balance and functional performance (e.g., mobility) in older adults, particularly because current efforts are primarily focused on lower extremity muscles. Based on these preliminary cross-sectional findings, it appears plausible to argue that trunk muscle exercises should be incorporated into intervention programs aiming at the promotion of balance, functional performance, and the prevention of falls in older adults. Cross-sectional studies have limitations because the outcomes from correlative analyses do not permit the identification of a cause-and-effect relationship. Accordingly, intervention studies have to be conducted to detect cause-and-effect relationships. The subsequent section will discuss intervention studies that examined the effects of trunk muscle exercise training (i.e., CST, PET) on

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measures of TMS, balance, functional performance, and falls in elderly people. 4.2 Effects of CST on Measures of TMS, Balance, Functional Performance, and Falls in Old Adults Evidence for the effectiveness of CST comes from different scientific subdisciplines. In rehabilitation, CST has been successfully used for the prevention of low back pain in healthy individuals and slow disease progression in patients with low back pain [46]. In sports medicine, CST has been advocated for the prevention of sports-related injuries as well as for performance enhancement [47]. These effects of CST have attracted attention in other scientific disciplines (e.g., geriatrics). In fact, a few studies have examined the effects of CST on TMS, balance, functional performance, and falls in elderly individuals. All 9 studies that met the inclusion criteria of this review reported significant improvements in measures of balance, functional performance, and/or falls following CST (Table 2). In a preliminary study, Petrofsky et al. [30] investigated the effects of a CST program using a commercial exercise device (i.e., 6-second abs machine) on maximal isometric strength of the abdominal and back muscles in healthy men and women aged 61–82 years. After 4 weeks of progressive training, significant strength gains were observed in trunk flexors (: 36 %, p \ 0.01, ES = 1.03) and trunk extensors (: 33 %, p \ 0.01, ES = 1.12) muscles. Further, Petrofsky and colleagues [30] demonstrated significant training-related improvements in maximum reach in the forward (: 45 %, p \ 0.01, ES = 1.34), right (: 22 %, p \ 0.01, ES = 0.66), and left (: 43 %, p \ 0.01, ES = 1.39) directions. Finally, tremor during the maximal forward reach task was significantly reduced in the 8 Hz (i.e., peripheral tremor) and the 25 Hz bands (i.e., central tremor) after training, indicating that peripheral (e.g., muscle spindles) and central (i.e., cerebellum, basal ganglia) adaptive processes could have occurred following training. However, these findings have to be interpreted with caution given that no control group was included in the study design that performed another physical activity known to improve balance. Katzman et al. [31] extended the findings of Petrofsky et al. [30] to a cohort of community-dwelling women aged 66–80 years with flexed posture (i.e., thoracic kyphosis of 50° or greater). Following 12 weeks of progressive trunk stabilization training (i.e., increase in load or Thera-band resistance), significant improvements were found in maximal isometric back extensor strength (: 60 %, p \ 0.001, ES = 1.42) and in the modified physical performance test (: 7 %, p \ 0.001, ES = 0.77). Further, a tendency towards enhanced performance was reported for gait speed

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(: 4 %, p = 0.06, ES = 0.28). However, given that no control group was incorporated into the study design, the observed performance improvements cannot explicitly be attributed to training. Sinaki et al. [29] examined community-dwelling women older than 60 years who suffered from osteoporotic kyphosis (i.e., Cobb angle of 50–65°). However, in contrast to Petrofsky et al. [30] and Katzman et al. [31], a control group consisting of healthy matched subjects of comparable age without kyphosis were also enrolled in the study. Based on their study design, Sinaki et al. [29] were able to substantiate the findings of Katzman et al. [31], in that they observed significant improvements in maximal isometric trunk extensor strength (: 38 %, p \ 0.001, ES = 1.17), in the sensory organization test (: 15 %, p = 0.003, ES = 0.85), in gait speed (: 7 %, p = 0.02, ES = 0.51), and in the falls efficacy score (; 58 %, p \ 0.001, ES = 1.37) following 4 weeks of a daily home-based dynamic exercise program for the trunk extensors. In randomized controlled trials, Hosseini et al. [22], Kang et al. [23], and Nichols et al. [24] scrutinized the effects of progressive core stability/strength training on measures of TMS, balance, functional performance, and fear of falling in healthy men and women aged 65–90 years. Following 6 weeks [22], 8 weeks [23], and 10 weeks [24] of training, there were significant improvements in the chair rise test (: 21 %, p = 0.51, ES = 0.04) [24], the weighted shelf-lift task (: 49 %, p = 0.013, ES = 0.08) [24], the one-legged balance test (: 22 %, p = 0.05, ES = 0.58) [24], tests for the assessment of weight support ability (: 11 %, p \ 0.05, ES = 0.86) and balance ability (: 27 %, p \ 0.05, ES = 0.44) [23], the functional reach test (: 20 %, p = 0.035, ES = 0.18) [24], the Y-balance test (: 46 %, p \ 0.001, ES = 2.37) [22], the dynamic gait index (: 42 %, p = 0.001, ES = 2.98) [22], the Reedco posture test (: 18 %, p = 0.002, ES = 0.39) [24], and the Berg balance scale (: 6 %, p = 0.01, ES = 0.20) [23]. However, no significant training-related improvements were observed in the four-scale fear of falling questionnaire (; 11 %, p = 0.21, ES = 0.63) [24], which could be explained by the fact that independently living healthy subjects with no cognitive impairment and no musculoskeletal/cardiovascular diseases were investigated. In the study of Hosseini et al. [22], the effects of CST were compared to those of traditional machine-based and free weight progressive strength training for the lower/upper extremities (e.g., leg press, squats). Strength training resulted in significant increases in the strength of the upper (bench press: : 36 %, p \ 0.05, ES = 2.44) and lower limbs (leg press: : 33 %, p \ 0.05, ES = 5.05), whereas CST did not cause any significant changes (bench press: : 14 %, p [ 0.05, ES = 1.25; leg press: : 10 %, p [ 0.05, ES = 1.54). Both strength

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training and CST improved balance (i.e., Y-balance test), with CST producing larger gains than strength training (strength training: : 31 %, p \ 0.001, ES = 1.61; CST: : 46 %, p \ 0.001, ES = 2.37). Further, CST (: 42 %, p = 0.001, ES = 2.98) but not strength training (: 14 %, p [ 0.05, ES = 0.15) resulted in enhanced gait stability (i.e., dynamic gait index). This indicates that CST is more effective at improving balance and mobility in old adults compared to traditional strength training. In more recent studies, Seo and colleagues [28] and Granacher et al. [21] extended the findings of the aforementioned studies by including an instability element (e.g., Swiss ball, balance pad) in their CST programs [21, 28]. Both studies investigated cognitively and physically healthy older adults with a mean age of 71 ± 4 [21] or 71 ± 7 years [28]. After 9 weeks [21] or 12 weeks [28] of progressive training, there were significant improvements in the maximal isometric strength of the trunk flexors/extensors/rotators (: 21–53 %, all p B 0.001, ES = 0.23–1.02) [21]. Further, training-induced performance enhancements occurred for the sit-to-stand test (: 9 %, p \ 0.05, ES = 0.20) [28], the arm curl test (: 3 %, p \ 0.01, ES = 0.18) [28], the one-legged standing test (: 10 %, p \ 0.01, ES = 0.09) [28], the timed up and go test (; 4–9 %, all p \ 0.05, ES = 0.39–0.66) [21, 28], the functional reach test (: 20 %, p \ 0.01, ES = 0.59) [21], the sit-and-reach test (: 24 %, p \ 0.001, ES = 0.52) [28], and the back scratch test (: 36 %, p \ 0.05, ES = 0.39) [28]. Finally, the intervention improved gait velocity (: 9 %, p \ 0.05, ES = 0.44) and gait variability (: 31 %, p \ 0.05, ES = 0.41) [21]. Given that gait variability is significantly greater in elderly community-dwelling fallers compared to non-fallers [48], and that core instability strength training has the potential to reduce gait variability [21], a hypothetical fall preventive effect of core instability strength training appears to be possible. However, future studies will have to examine this intriguing possibility. Furthermore, CST conducted with unstable devices (e.g., Swiss ball) needs to be carefully prescribed and progressed. More specifically, the magnitude of individual effort along with the systematic structuring of the instability CST must be supervised by experts. A key factor in the design of any instability CST is appropriate program design, which includes a safe training environment, proper exercise instruction, qualified supervision, as well as the correct prescription of the program variables (i.e., training intensity; training volume; training frequency; number of exercises, sets, reps, etc.). A limitation of the reported studies is that the current state of knowledge does not allow us to determine the mechanism of how a more stable and stronger core (i.e., trunk extensors/flexors and the skeletal structures of the trunk) improves balance/mobility and prevents falls. It is


possible that enhanced core strength/stability or a combination of the two would allow old adults to use their upper and lower extremities more effectively by optimizing trunk movements, the mechanical linkage between upper and lower extremities, and by increasing the effectiveness of corrective movements in precarious situations of daily life. In summary, CST is an effective training regimen for the promotion of TMS, balance/mobility, and functional performance in older healthy subjects and in persons with a flexed, kyphotic trunk posture. There is further evidence that CST has an impact on fear of falling and fall efficacy. Whether it has the capability to reduce fall rate in older adults is currently unresolved. However, there is indirect support originating from gait variability data that CST has the potential to reduce the number of falls in older adults. Compared to traditional strength training, CST results in more pronounced effects regarding balance and mobility in older adults. The mechanisms behind these effects are currently unresolved. Based on the available studies [21, 28], the inclusion of unstable elements (e.g., balance pads, Swiss balls) in CST is recommended. The design of future studies should include CST with and without unstable devices to determine whether the instability component in training has an additional effect on measures of TMS, balance, functional performance, and falls. Given that the mean quality score for the nine included CST studies averaged 4.5 ± 1.6 (range 3–8) on the PEDro scale, and that only two studies [21, 34] reached the predetermined cut-off of C6 [16], there is a need for more high-quality studies to explicitly identify the relevance of CST for the elderly population. 4.3 Effects of Pilates Exercise Training (PET) on Measures of Trunk Muscle Strength (TMS), Balance, Functional Performance, and Falls in Old Adults The Pilates method was created by the German American physical-culturist Joseph Pilates (1883–1967), who originally combined exercise, movement, philosophy, gymnastics, martial arts, yoga, and dance into a body-conditioning routine [49]. Pilates-based exercises are designed to promote core stability/strength, flexibility, coordination, and balance [50]. It is practiced on mats and/or with different types of Pilates apparatus (e.g., reformer, Pilates ring). Over the last 10 years, PET has become an increasingly popular exercise modality in fitness settings [49] and has attracted researchers’ attention. In fact, a PubMed search of the last 10 years (i.e., 2002–2012) of the literature revealed 66 articles with the keyword ‘‘Pilates’’ in the title. Five studies were eligible for inclusion in this review and will be discussed in the following (Table 3).

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Two preliminary studies [32, 33] investigated the effects of PET on measures of balance, functional performance, and fall risk in healthy community-dwelling men and women aged 67–71 years [32] and 60–76 years [33]. Following 8 weeks of progressive PET, significant performance enhancements were found in a two-legged stance test on an unstable surface with the eyes closed (; 27 %, p \ 0.05, ES = 0.99) [32], in the maximal balance range test (: 8–12 %, all p \ 0.05, ES = 0.65–0.69) [32], in the timed up and go test (; 7 %, p \ 0.05, ES = 0.56) [32], and in gait speed (: 27 %, p \ 0.05, ES = 1.27) [33]. However, in the study of Newell et al. [33], gait variability (; 55 %, p [ 0.05, ES = 0.75) and the fall risk index (; 2 %, p = 0.09, ES = 0.65) were not significantly changed after training. This result has to be interpreted with caution given that the study was statistically underpowered (i.e., 9 subjects) and that no control group was included. There is evidence, however, from randomized controlled trials indicating that PET has the potential to improve measures of TMS, balance, and functional performance [25–27] in healthy older men and women aged over 60 years. In fact, 5 weeks [25], 8 weeks [27], or 12 weeks [26] of progressive PET resulted in improved performance in the maximal isometric strength of the hip muscles (: 40 %, p \ 0.05, ES = 0.99) [26]. Further, training-induced enhancements were found in a dynamic two-legged stance test (; 17–18 %, all p \ 0.05, ES = 0.46–0.99) [25, 26], in the four-square step test (; 7 %, p = 0.001, ES = 0.44) [25], in the timed up and go test (; 7 %, p \ 0.001, ES = 0.34) [25], in the Tinetti test (: 4 %, p = 0.009, ES = 1.27) [27], in the sit-and-reach test (: 25 %, p \ 0.05, ES = 0.93) [26], and in the functional autonomy test (; 9 %, p \ 0.05, ES = 0.49) [27]. The most interesting finding comes from the study of Irez et al. [26]. These authors observed a lower number of falls (; 80 %, p \ 0.01, ES = 0.99) in the Pilates exercise group as compared to the control group after training, indicating that PET is an effective fall-preventive intervention program. In summary, PET has an impact on different measures of TMS, balance, functional performance, and falls in healthy older adults. Notably, the randomized controlled trial of Irez et al. [26] showed convincing results in all investigated parameters (i.e., strength, balance, functional performance, occurrence of falls). This study was longer in duration (i.e., 12 weeks) than all other studies (i.e., 5–8 weeks). Based on this preliminary qualitative analysis, it could be hypothesized that longer PET periods are more effective than shorter ones. Future studies have to be conducted that elucidate this issue. The mean quality score for the five included PET studies averaged 5.2 ± 2.3 (range 3–9) on the PEDro scale, and lies a little higher than the mean PEDro score of the CST studies (i.e., 4.5 ± 1.6). Again, only one study [25] reached the predetermined

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cutoff of C6 [16], which indicates that the overall study quality is rather weak. Thus, future studies should specifically focus on the methodological quality of their PET approach.

5 Conclusions The importance of core strength/stability for sufficient balance and functional performance as well as for the avoidance of falls has been overlooked for a long time by geriatric researchers. Twenty cross-sectional (n = 6) and longitudinal (n = 14) studies indicate that core strength/stability is important for the successful performance of activities of daily living in old age. More specifically, a stable and strong core may contribute to more efficient use of the lower and upper extremities and improved balance/functional performance in older adults. Based on the findings of this systematic literature review, CST and/or PET can be used as an adjunct or even alternative to traditional balance and/or resistance training programs for older adults. Further, CST and PET are easy to administer in a group setting or in individual fallpreventive or rehabilitative intervention programs because little equipment and space are needed to perform such exercises. Acknowledgments This work was supported by a grant from the German Research Foundation (MU 3327/2-1). The authors have no conflicts of interest that are directly relevant to the content of this review.

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