Balance Improvements in Older Women: Effects of Exercise Training

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awcises would improve the angle-stance balance of healthy older women and ... domized control trial compared the effects of two exercise programs on static.
Research Report

Balance Improvements in Older Women: Effects of Exercise Training

Backgruund and Purpose. Loss of lower-extremity strength increases the risk of falk in older persons. The purpose of this study was to test the hypothesis that a vigorous program of lower-atremirystrengthening, walking, and postural control awcises would improve the angle-stance balance of healthy older women and lower their risk of falls and fall-associated injuries, Subjects. From a total of 38 respo:ndents,21 women were randomly assigned to either a treatment group (combined training, n =12) or a control group flexibility training, n =9). The subjects ranged in a g e j k m 62 to 75years @=68, SD=3.5). MetbocCs. A randomized control trial compared the effects of two exercise programs on static balance. The combined training group exercised three times per week o n knee extension and sitting leg press mchines, walked b&[v for 20 minutes, and performed postural contml exercises, which included simple tai chi movements. The jm'bility training group pe@ormed postural control exercises weekly Measurements of balance were obtained on a force platfonn in double and single stance, at baseline and following 6 months of exercise training. Results. Double-stance measurements were unchanged a@er training. The mean displacement of the center of pressure in single stance improved 17% in the combined training group and did not change in the flexibility training group. A repeated-measuresanalysis of variance revealed that the dt@rence in improvement between the combined training andjexibility training groups was not signficant. Discussion and ConcZusion. This is the first intervention trial to demonstrate improuements in single-stancepostural sway in older women with exercise training. Additional studies with more subjects will be needed to determine whether a combined training program of resistance training, walking, and postural exercises can improve balance more than a program of postural control exercises alone. [JudgeJO, Lindsey C, Underwood M, WinsemiusD. Balance improvements in older women: eficts of exercise training. Pbys Ther. 1993;73254-265.1

James 0 Judge Carleen Lindsey Michael Underwood Davld Wlnsemlus

Key Words: &ed; Equilibrium; Exercise, general; Posture, general; Women.

The prevention of falls and the substantial morbidity associated with fall-related injuries will become increasingly important for preserving the health and independence of older women. Fall risk has been shown to increase with reduced lowerextremity joint moments, weakness on manual muscle testing, and diaiculty arising from a chair.'-3 Previous studies4,5have shown decrements in muscle mass, force production per cross-

sectional area of muscle, and isokinetic joint moments in several lowerextremity muscle groups with usual aging. This weakness may be an important and potentially reversible component of instability during routine daily activities, predisposing the elderly to falls, Although some researchers6.' have demonstrated that older adults are capable of significant improvements in lower-extremity force measures with resistance train-

Physical Therapy /Volume 73, Number 4/April 1993

ing, the effect of this type of training on balance measures has not been reported. Postural sway increases with usual aging. Cross-sectional studies have used force platforms, which record the center of pressure (center of reaction force), to estimate body sway.8 Older persons have slightly higher measures of sway in double stance when compared with younger 254 / 53

subjects.9 Increased postural sway increased the risk of falls in studies of communitydwelling elderly.lGl3 Differences in sway with age are accentuated during testing in singlestance postures. Single-stance sway measures are threefold greater in older subjects than in younger subjects.10 Single-stance time (time able to stand on one foot) declines with age,14and in advanced age, few persons are able to stand on one leg for more than several seconds." Singlestance time was correlated with a summary hip isometric moment score.15 Two intervention studies16J7 demonstrated that balance training programs that included performing single-stance postures increased single-stance time. Because the majority of falls occur during walking or turning or on stairs,lBz19 we hypothesized that improved single-stance control may lower the risk of falls and fallassociated injuries. Two previous exercise studies emphasizing postural control demonstrated no improvements in single-stance20 o r doublestance balance.21 The exercise interventions in these studies did not include lower-extremity resistance training. Single-stance balance requires appropriate contraction of several lower-extremity muscle groups in addition to adequate vestib-

ular function and proprioception. Our study tested the hypothesis that a vigorous and frequent program of lower-extremity strengthening, walking, and postural control exercises would improve single-stance balance in healthy older women, compared with a program of postural control exercises performed once a week. Studies have used different measures derived from the force-plate data. Force-platform data are used to estimate the movement of the center of mass of the standing subject from the movement of center of force (COF) on the p l a t f ~ r mTwo . ~ intervention studies20121have used the mean velocity of COF movement during stance. The measure reported in this study is the mean displacement (DISP) from the average position of the COF during each trial, and is similar to the outcome used in a recent crosssectional study.22The DISP measure assumes that the mean coordinates of the COF obtained from 8 seconds of sampling represents the subject's true "center of balance" o r neutral position. A longer period of sampling might give a more stable estimate of the subject's neutral position, but few subjects are able to stand in single stance for very long, and the effect of fatigue of the muscles controlling the hip and foot might affect the neutral position of the COF.

J O Judge, MD, is hsistant Professor of Medicine, Travelers Center on Aging, University of Connecticut School of Medicine, Farmington, CT 06030. Address all correspondence to Dr Judge at Travelers Center on Aging-5215, IJniversity of Connecticut Health Center, Farmington, CT 06030 (USA). C Lindsey, PT, is Physical Therapist, Department of Rehabilitation Services, University of Connecticut Health Center. M Underwood, MD, is Assistant Professor of Medicine, Travelers Center on Aging, University of Connecticut School of Medicine.

D Winsemius, MD, is Assistant Professor of Medicine, Travelers Center on Aging, University of Connecticut School of Medicine. Dr Judge's work was supported by the Pfizer/Arnerican Geriatrics Society Postdoctoral Fellowship Program. The research was performed at the University of Connecticut Health Center, Newington Children's Hospital, and the Taking Care Center, Hartford, CT, and was supported by a grant from the Dana Foundation. This protocol was reviewed and accepted by the Institutional Review Boards of the University of Connecticut Health Center and Newington Children's Hospital. Preliminary reports of this work were presented at the 1990 and 1991 meetings of the American Geriatric Society. This article was submitted December 26, 1991, and was accepted November 20, 1992.

54 I255

Method Study Design and Recmitment A randomized control trial design was used to test whether an exercise program that was performed frequently and included resistance training, brisk walking, and flexibility and postural control exercises (combined training) would be superior to a program that was performed once a week and included only flexibility and postural control exercises (flexibility training).

Subjects were recruited by mail from a population of more than 1,300 female retirees or spouses of male retirees of a large Hartford (Conn) insurance company. Subjects completed a medical history screening and physical examination and performed a symptom-limited exercise stress test using a modified Balke protocol.23 Individuals with the following diagnoses were excluded: coronary or carotid artery disease, neurologic disease, postural hypotension (> 15 mm Hg systolic pressure o r > 10 mm Hg diastolic pressure at 3 minutes), malignancy (excluding skin), rheumatoid arthritis, hip o r knee joint replacement, or obesity (body mass index >30.5 kg/m2). Because the effects of exercise on bone density were tested in a separate part of our study, subjects taking medications that are known to affect bone density (furosemide, prednisone, estrogen) were also excluded. Subjects who were regularly exercising more than 2 hours per week were excluded. Individuals with symptomatic lower-extremity arthritis were allowed to participate if passive range of motion was unrestricted. Subjects gave written informed consent prior to participation in the study. A total of 114 women responded (8%

response rate), of whom 30 women did not wish to participate or did not complete the screening process. Of the remaining 84 potential subjects, 46 women were excluded for medical reasons, and 38 women completed the screening process in three groups. Subjects were randomized to either a combined training o r flexibil-

Physical Therapy /Volume 73, Number 4/April 1993

,

ity training group using a randomiza-

tion rate of 0.55 or 0.45, respectively, based on the assumption that the combined training group would have a higher ;attrition rate. The flexibility training group was considered to be a control group for the combined training group. Balance measurements were obtained on the first two groups recruited (n=30). Twenty-five of the 30 subjects in the first two groups volunteered to participate in balance assessments, which required traveling to a gait laboratory in a neighboring town for balance measurement. Repeat measurements were obtained on 21 subjects (12 combined training, 9 flexibility training). Four subjects dropped out or were unable to return for repeat testing for personal reasons. Balance Measurement Postural sway measurements were obtained from an AMTI OR4 force platform:' at the Newington Children's Hospital Gait Laboratory (Newington, Corn). The platform uses strain gauges to measure three orthogonal force components. The force moments were used to calculate the position of the COF in the x and y dimensions. The force platform output was amplified and &gitizedt at 100 Hz per channel. We used AMTI software to calculate the DISP (in centimeters) for each tnal.This measure combines displacement in the sagittal plane (anteriorposterior dimension of the foot) and the frontal plane (lateral dimension of the foot). The Appendix contains the equation that was used to calculate this measure. Basehe: measurements were obtained before the exercise program began. Twenty-one subjects had follow-up measurements of postural sway after 6 months of exercise. Subjects wore flat-heel, rubber-soled shoes, and four

conditions were tested in sequential order for each subject. Three trials of each condition were recorded, and the average displacement for the three trials is reported. There were two double-stance postures. For double stance, the subjects placed their feet together, with their arms held at their sides. Testing was performed with eyes open (EO) and with eyes closed (EC). There were two single-stance conditions. In single-stance conditions, subjects shifted their weight to the dominant foot (as determined by subject's selfreported dominant hand) before raising the opposite lower extremity. In upright single stance (USS), the nondominant lower extremity was held in 0 degrees of extension at the hip, and the knee was flexed 80 to 90 degrees. In forward-leaning single stance (FSS), subjects flexed their nondominant hip 10 to 15 degrees with the knee fully extended and leaned forward, placing pressure on the anterior foot. An acrylic panel 5 mm in height was placed under the heel to assist in displacing the force to the anterior part of the foot. The average displacement of the COF during three trials for each condition is reported. To create a summary variable for single stance, the displacements of the six trials in the two single-stance conditions (USS, FSS) were averaged. This summary singlestance measure was the primary outcome variable for the study. To minimize learning effects while on the platform, subjects practiced the postures three times during the initial screening examination and again on the day of testing. Subjects attempted to maintain each posture for 13 seconds, with COF data recorded for the final 8 seconds in each stance. If a

'AMTI Inc, 141 California St, Newton, MA 02158.

t ~ o d e flT l 28014 Data Translation Inc, 100 Locke Dr, Marlborough, MA 01752-1192 *Eagle knee extension, multi-hip resistance machines, Cybex, Div of Lumex Inc, 2100 Smithtown Ave, Ronlronkoma, NY 11779. keiser Sports Health Equipment, 411 S West Ave, Fresno, CA 93706-9952

Physical Therapy /Volume 73, Number 4/April 1993

subject lost her balance o r placed the suspended foot on the floor, data from the attempt were not saved, and she was given an additional attempt. The mean of three successful attempts is reported for each condition. Visual reference was provided by a landscape poster placed 1 m in front of the platform. Force Measurement

Force measurements, using single maximal repetitions (I-RMs), were obtained on muscle variable-resistance machines for knee extensionz and a sitting leg press' on separate days, with a minimum of 2 days between measurements. Subjects performed five lifts with low resistance to warm up, and then resistance was increased, based on the subjects' perceived d f i culty (rated 1-4 for easy to very hard), until the subjects could not complete a lift (failure). Subjects rested at least 1 minute between lifts. The protocol goal was to reach the I-RM in four or five attempts, but occasionally six or seven lifts were required before a failure occurred. Verbal encouragement before and during each lift was given to the subjects. To reduce the effect of repeated testing on force measures, subjects performed two baseline I-RM tests, separated by at least 1 week, with the second test recorded as the baseline force measure. Testing the reliability of force measures was not part of the study design. Knee extension I-RMs were performed in a sitting position, with the back supported and the hip flexed at 90 degrees at an angular velocity of about 45 degrees. A knee extension attempt was considered successful if the subject was able to extend the bar from 90 to 10 degrees of knee flexion, using a range-limiting device at 10 degrees to increase the reproducibility of the measure. Knee extension force results are reported in units of extension moment (newton-meters), not corrected for lower leg mass. The maximum machine moment at the axis of rotation (torque) occurs at between 40 and 50 degrees of knee 256 / 55

flexion; at full knee extension, the torque is 85% of maximum. For the sitting leg press, a back s u p port (GO0 from the horizontal) was adjusted by moving horizontally to compensate for differences in the subjects' thigh length. The starting position was set at a knee flexion angle of 90 degrees, with hip flexion of approximately 105 degrees and ankle dorslflexion of approximately 5 degrees, performed at an angular velocity at the hip of 30°/s. Subjects were instructed to lift the crossbar or move the footplate slowly and to complete a movement. Verbal encouragement was given during all attempts. Maximal force at the footplate, which occurred at the initiation of the movement, was recorded in newtons. Force was determined by measuring the air pressure in the cylinder (in pounds per square inch) xcrosssectional area of the cylinder (in square inches) ~ 4 . 4 4 8 2NAb. A straingauge dynamometer was used to confirm the accuracy of the calibration of air pressure over the range of forces found in the study.

Aerobic Capacify An estimate of fitness was determined from the treadmill time on a symptom-limited stress test using a modified Balke protocol.23 Maximum treadmill speed was 1.4 rn-s-' (3.3 mph) and is reported as metabolic equivalents (1 MET=3.5 mL 0,-kg-'smin-I).

Intewentlon-Combined Treatment Group Resistance training.The musclestrengthening exercises used variable resistance machines providing knee and hip extension' and a sitting leg press.§ Three sets of bilateral exercise were performed in knee extension and sitting leg press, with a resistance set at about 70% of 1-RM. Subjects exercised to volitionalfatigue, which was defined as the maximum number of lifts a subject could perform before failure of the movement occurred. Subjects performed between 10 and 14 repetitions per set, with 2 to

3 minutes of rest between sets. Knee extension exercises were performed in a sitting position, with the back supported, at an angular velocity of about 4j0/s, with a 1-second pause at full extension. The sitting leg press exercise was performed as in the 1-RM testing, with the back support position adjusted for subject leg length. The exercise involved combined hip extension (from about 105" to 60" of flexion), knee extension (from 90" to 0" of flexion), and ankle plantar flexion (from about 5" of dorsiflexion to 15" of plantar flexion), performed at an angular velocity at the hip of 30°/s. The resistance settings were greatest in the second set, and were 5% to 7% lower in the third set to permit completion of 10 to 14 repetitions. Resistance was adjusted weekly by the exercise leader, based on a review of the subject's performance. Resistance was increased when a subject could consistently complete more than 12 repetitions at a given resistance. A 1-RM test was performed every 8 to 10 weeks, and further adjustments in the resistance setting were made to keep the resistance at 70% of 1-RM for leg press and knee extension. Standing hip extensions were performed unilaterally, subjects stabilized their position by holding onto a horizontal bar just below shoulder level. Two sets of 20 repetitions each were performed at a resistance that permitted maintenance of "good form," defined as the completion of the movement in a smooth, nonjerking fashion with maintenance of lumbar lordosis. The lower resistance in the hip extension protocol was made to decrease the risk of lower back injury. There was close supervision of the resistance exercises by the exercise leaders. One leader s u p e ~ s e dthe knee extension and hip extension machine, and the other s u p e ~ s e d the sitting leg press. Frequent feedback and instruction on correct form were given to each subject.

Walking.Subjects walked for 20 minutes on a 145-m indoor track,

with a heart rate goal of 70% of each subject's maximum heart rate recorded at the baseline exercise treadmill test. After the seventh or eighth month, most subjects had reached a maximal walking velocity and were completing the walk with a heart rate below 70% of maximal heart rate. The number of laps walked, walk time, and preexercise and postexercise pulse rate were recorded at each session initially by the exercise leaders and after 2 or 3 months by the subject, with periodic checks by the exercise leaders.

Flexlblilty and balance. Neck and shoulder girdle flexibility, trunk lateral rotation, and thoracic extension exercises were performed in a standing position. Static stretch of the hip adductor and hamstring muscles was performed in a sitting position on a mat, with hips abducted and laterally (externally) rotated, with attention to limit lumbar and thoracic flexion while leaning fo~ward.Subjects were taught to rise from a prone o r supine position to a standing position. From the supine position, a "log-roll" turn (legs flexed at hip and knee and limiting trunk rotation) brought subjects to a side-lying position, and then to a quadrupedal position and a half-kneel position with one knee on the mat and the opposite foot on the mat. A vertical rise completed the movement, with attention to knee/thigh alignment (first ray of foot, patella, and anterior superior iliac spine in same plane) and upright torso. The exercise progressed from using a chair for stability to rising without a chair support, placing the hand on the thigh for stability during vertical rise. Subjects performed mock housecleaning tasks in a "lunge" posture, similar to that used in fencing, which emphasized movement at the knee and hip without spine flexion. Following the stretching exercises, subjects performed low-resistance hip abduction exercises. Abduction exercises were performed in a side-lying position on a mat, with the dependent leg flexed at the knee and hip. Subjects were taught to keep the thigh at full (0") extension and neutral rota-

Physical Therapy/Volume 73, Number 4/April 1993

tion (0")hrough the ROM of the exercise (about - 10" to 35"). Two sets of contractions were performed, initially w.ith no weights, to fatigue or a maximum of 20 repetitions. Ankle weights (1-2 Ib) were added when subjects could perform two sets of 20 repetitions each, maintaining good form as defined above. Pelvic tilt exercises were taught in the supine position with knees and hips flexed and feet on the mat. Following pelvic tilt exercises, bilateral hip extensions, or "bridging" exercises, were performed while remaining in a supine position. Legs were aligned so that there was no genu varus o r valgus, and feet .were flat on mat, a shoulder distance ,apart.The buttocks were raised slowly about 10 to 15 cm by extension at the hips and pelvic tilt, and then slowly lowered. When two sets of 12 repetitions each were performed with good form, unilateral exercises were performed, with the nonexercised leg held in the hooklying position. Simplhed tai chi exercises, which involve slow and controlled movements of the body, were performed.Z4 Correct trunk and lower-body alignment in the standing position was stressed, and subjects were taught to focus on how weight was distributed on the feet. Subjects exercised in a large room with floor-length mirrors, which provided visual feedback to their posture during the movements. Slow, controlled forward and backward steps were performed as a warm-up. Other movements included lateral and anterior-posterior weight shifts, single-stance postures, and turning and pivoting with weight on the heel or forefoot, while keeping the torso upright and the knees slightly flexed. Arm movements were added after subjects were proficient in leg movements.

htenrentlon-FlexlbiMy Trainlng Group The flexibility training group performed no exercise for the first 12 weeks. After week 13, the group exercised once weekly for 30 minutes and performed the same flexibility and balance exercises as the combined training group. They did not use ankle weights for hip abduction exercises, however, and they performed bilateral (not unilateral) bridging exercises. Subjects were not permitted to participate in any other organized exercise program, but were permitted to perform the exercises at home. All exercise sessions for both groups were led by a physical therapist, a master's degree level exercise scientist, or a physician.

Compllance Compliance with the exercise program was monitored by regular attendance taken by exercise supervisors, who led the exercise sessions, obselved the resistance training, and recorded resistance and repetitions performed. Subjects were taught to obtain pulse rates, and they recorded the number of laps walked, preexercise and postexercise pulse rate, and walk time. Accuracy of pulse recordmgs were checked by an exercise leader monthly. Pulse sensor wristwatches were used by subjects who had difficulty determining their pulse rate. Mean attendance was 80% for both groups, and all subjects attended more than 50% of the exercise sessions.

Comparability of the combined training and flexibility training groups at baseline was assessed by independent t tests. The null hypothesis was that the improvement in DISP in single stance of the combined training group would not differ from that of the flexibility training group. The primary outcome variable was the mean DISP of the COF during the six

~~SYSTAT Ilnc, 1800 Sherman Ave, Evanston, IL 60201.

Physical Therapy /Volume 73, Number 4/April 1993

trials of the two single-stance conditions (USS and FSS). A two-tailed paired t test was used to determine whether each group had improved (reduced) the DISP during balance testing. Repeated-measures analysis of variance (ANOVA) was tested for the effect of group assignment (combined training or flexibility training) on single-stance balance outcomes. The same analytic strategy was used for the muscle force measures. To test for within-session learning, the results from trials 1 to 3 for each condition were analyzed by ANOVA. Pearson Product-Moment Correlation Coefficients determined the relationships between single-stance and double-stance measures and between muscle force o r fitness measures and balance measures. All statistical analysis was performed using SYSTAT 4.0 software!' The level for significance of all results was set at .05.

Resutts Baseline The baseline characteristics of the two groups were similar for all variables tested (Tab. 1).

Balance Measures The results for single stance are from 12 subjects in the combined training group and 9 subjects in the flexibility training group. Three subjects had a single failure during single-stance testing at baseline, but completed three successful single-stance tests and were included in the analysis. The summary single-stance measure (the mean DISP of the six singlestance trials) improved 18% in the combined training group at posttest, from 0.8320.19 cm to 0.6720.08 cm (4,32% 95% CI, P=.023). This measure did not significantly improve (5%, -9,19% 95% CI) in the flexibility training group (0.77+0.08 cm to 0.73+.0.10cm, P=.3). The repeatedmeasures ANOVA found a trend for the improvement in the combined

-

Table 1. Baseline Measurements

Age (Y)

Combined Training Group (n= 12)

Flexlblllty Tralnlng Group (n=9)

X

X

SD

Range

SD

Range

67.8

2.8

64-73

68.5

4.1

62-75

Height (cm)

161.0

6.3

147-1 72

160.2

7.6

155-166

Weight (kg)

58.3

6.9

4747

64.5

10.7

49-79

BMla

22.8

3.6

17-28

26.8

4.8

19-30

METb

8.2

1.3

7.6

1.2

5.0-9.4

5.S10.7

-

17.3,P>.001). Sitting leg press measures significantly improved at repeat testing (F=58.9, P