The role of exercise intensity and cortisol

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Effects of exercise on cravings to smoke: The role of exercise intensity and cortisol Filippe Scerbo a; Guy Faulkner b; Adrian Taylor b; Scott Thomas a a Faculty of Physical Education and Health, University of Toronto, Toronto, Ontario, Canada b School of Sport and Health Sciences, University of Exeter, Exeter, UK First published on: 04 December 2009

To cite this Article Scerbo, Filippe, Faulkner, Guy, Taylor, Adrian and Thomas, Scott(2009) 'Effects of exercise on cravings

to smoke: The role of exercise intensity and cortisol', Journal of Sports Sciences,, First published on: 04 December 2009 (iFirst) To link to this Article: DOI: 10.1080/02640410903390089 URL: http://dx.doi.org/10.1080/02640410903390089

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Journal of Sports Sciences, 2009; 1–9, iFirst article

Effects of exercise on cravings to smoke: The role of exercise intensity and cortisol

FILIPPE SCERBO1, GUY FAULKNER2, ADRIAN TAYLOR2, & SCOTT THOMAS1 1

Faculty of Physical Education and Health, University of Toronto, Toronto, Ontario, Canada and 2School of Sport and Health Sciences, University of Exeter, Exeter, UK

Downloaded By: [Canadian Research Knowledge Network] At: 15:22 8 December 2009

(Accepted 6 October 2009)

Abstract Research consistently demonstrates that a bout of moderate exercise alleviates cravings to smoke among abstaining smokers. The aims of this study were to examine whether doses of exercise (moderate or vigorous) reduced cravings differently, and whether reductions in cravings were associated with changes in cortisol concentration. Using a within-participant, crossover design, 18 participants conducted three 15-min treatment sessions on separate days: passive, walking (45–50% heart rate reserve), and running (80–85% heart rate reserve) conditions. Participants rated cravings at baseline, mid-treatment, and 0, 10, 20, and 30 min after each treatment. Salivary cortisol samples were collected at baseline, immediately after, and 30 min after each condition. Significant group 6 time interactions were identified, demonstrating significant reductions in craving items after the walking and running conditions compared with the passive control. No significant differences in craving reductions were found between walking and running conditions. Post hoc comparisons found that running condition cravings to smoke scores were reduced for a longer duration post-treatment than post-walking condition scores. The decline in cortisol concentration was attenuated in the running group only. Vigorous exercise has a similar effect to moderate exercise in terms of the magnitude of craving reduction. However, performing bouts of moderate-intensity exercise may be a better recommendation for reducing cravings.

Keywords: Exercise, smoking cessation, cravings, cortisol

Introduction There is increasing evidence that exercise plays an important role in the acute management of cigarette cravings and withdrawal symptoms predictive of smoking relapse. Taylor and colleagues (Taylor, Ussher, & Faulkner, 2007) reported that in nine of the ten studies reviewed, an acute bout of exercise significantly reduced cravings [with effect sizes (Cohen’s d) of 0.51–4.6] and withdrawal symptoms (e.g. anxiety, stress, tension, poor concentration, irritability, and restlessness). Briefly, participation in 10- to 15-min bouts of continuous low- to moderateintensity (45–55% heart rate reserve) physical activity, such as brisk-paced walking or cycling, has beneficial effects in temporarily abstinent smokers, which last up to 20 min post-exercise (Taylor et al., 2007). A brief bout of low-intensity movement (i.e. isometric exercise) also reduces cravings to a lesser extent, and for only 10 min (Ussher, West, Doshi, & Sampuran, 2006a). Exploration of the mechanisms

involved has been limited but existing research at least suggests that distraction and expectancy of an effect are not the primary factors underlying the observed reductions in cravings and withdrawal symptoms (Daniel, Cropley & Fife-Schaw, 2006, 2007; Daniel, Cropley, Ussher, & West, 2004). A number of questions, with important practical relevance, remain unanswered. Primarily, what psycho-physiological changes, during and after exercise, mediate the effects on cravings? Evidence of plausible mechanisms is needed to support the notion of causal effects of exercise on reduced cravings. Several possible pathways, including cerebral dopaminergic activity, ß-endorphins, and salivary cortisol concentration change, merit further investigation (Janse van Rensburg, Taylor, Hodgson, & Benattayallah, 2009; Taylor et al., 2007). An additional question relates to the impact of exercise intensity on cravings. Does exercise performed at a vigorous intensity reduce cravings more than exercise of a moderate intensity or of a longer duration?

Correspondence: G. Faulkner, Faculty of Physical Education and Health, University of Toronto, 55 Harbord Street, Toronto, Ontario M5S 2W6, Canada. E-mail: [email protected] ISSN 0264-0414 print/ISSN 1466-447X online Ó 2009 Taylor & Francis DOI: 10.1080/02640410903390089


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Alternatively, it has been suggested that the elevated stress and activation caused by vigorous exercise may even acutely heighten cravings (Taylor & Ussher, 2005). A recent study examined the effects of moderate and vigorous exercise and a passive condition on cigarette cravings and withdrawal symptoms in abstaining smokers (Everson, Daley, & Ussher, 2008). Forty-five regular smokers were randomly assigned to 10 min of either moderate- (40–59% heart rate reserve) or vigorous-intensity (60–84% heart rate reserve) cycle ergometry, or a passive waiting condition. Compared with the passive condition, both exercise conditions were beneficial in reducing cravings during and for 5 min after the exercise bout. While no effects lasted for 30 min, only the moderate-intensity exercise reduced withdrawal symptoms up to 5 min after exercise. Notably, vigorous exercise was associated with adverse mood outcomes during exercise. Consequently, Everson and colleagues (2008) suggested that mood may not be a primary mechanism through which exercise reduces cravings, and recommended future research exploring the possible mechanisms underpinning the beneficial effect of brief bouts of exercise on cravings to smoke. Cortisol, the body’s primary stress hormone, released through the hypothalamic–pituitary– adrenocortical (HPA) axis, is the mechanism of interest in the current study due to its unique interactions with both physical activity and smoking behavior, in addition to its implications for overall health. Acute smoking has been shown to stimulate release of cortisol, and long-term smokers experience cortisol concentrations that are typically 36% higher than that of non-smokers (Steptoe & Ussher, 2006), depending on the number of cigarettes smoked (i.e. higher in heavy smokers than light smokers) (Ussher et al., 2006b). Elevated cortisol, which typically results from chronic stress, has a range of adverse biological consequences, from elevating lipid profiles and promoting central adiposity to depressing immune function, bone mineral density, and reproductive function (Steptoe & Ussher, 2006). Interest in cortisol as a mechanism is largely based on what we already know about addiction processes. Upon cessation of smoking, large reductions in cortisol are seen within the first 12 h (Pomerleau, Garcia, Pomerleau, & Cameron, 1992) and 24 h of abstinence (Steptoe & Ussher, 2006; Ussher et al., 2006b), and steeper declines in cortisol concentration during this early stage of cessation is predictive of exacerbated withdrawal symptoms and relapse (al’Absi, Hatsukami, Davis, & Wittmers, 2004; Frederick et al., 1998; Rasmusson, Wu, Paliwal, Anderson, & Krishnan-Sarin, 2006).

A range of proposed mechanisms may explain the relationship between reductions in cortisol and these outcomes. The stimulating effects of cortisol might contribute to the reinforcing properties of smoking such that cortisol declines might be distressing for the smoker (Ussher et al., 2006b). An increased nicotine receptor sensitivity associated with a reduction in cortisol may exacerbate withdrawal symptoms (Pomerleau & Pomerleau, 1990). Although such mechanisms have yet to be confirmed (Ussher et al., 2006b), it does raise the question as to whether attenuating these dramatic declines during attempts to quit may in turn alleviate withdrawal symptoms. Specifically, vigorous-intensity exercise has been shown to increase cortisol concentrations among non-smokers (Jacks, Sowash, Anning, McGloughlin, & Andres, 2002; McGuigan, Egan, & Foster, 2003; Nieman, Henson, Austin, & Brown, 2005) and nonabstaining smokers (Pomerleau et al., 1987). However, no study has investigated the effects of exercise (moderate or vigorous intensity) on cortisol among abstinent smokers who are experiencing elevated cigarette cravings. The purpose of the present study was to examine the acute effects of high-intensity exercise on cravings, compared with moderate-intensity exercise and rest. Since vigorous- rather than moderateintensity exercise is likely required for changes in cortisol concentration (Allgrove, Gomes, Hough, & Gleeson, 2008), we also examined whether reductions in cravings were related to this physiological measure. It was hypothesized that there would be an attenuation in the decline of cortisol in the vigorous condition and that this attenuation would be associated with reductions in cravings.

Methods Participants The study was approved by the University Research Ethics Board and all participants gave their informed consent prior to their inclusion in the study. Regular smokers (smoking at least ten cigarettes daily for the past 3 years) were recruited through public advertisements posted on online message boards and through notices and leaflets distributed across the campus. They were excluded if they were pregnant, taking prescription medication, receiving treatment for any physical or psychological condition, had contraindications to do vigorous physical activity (American College of Sports Medicine, 2005), or were currently attempting to cut down or quit smoking (including taking nicotine replacement therapy or other pharmacological aids). Effect sizes previously reported (Daniel et al., 2004; Taylor & Katomeri, 2006; Ussher, Nunziata,

Exercise intensity and cravings to smoke Cropley, & West, 2001) suggested that a sample size of 15 participants would yield a power of 0.8 (twotailed alpha of 0.05), sufficient to detect differences in cravings, for a within-participant design. Previous studies involving 10–17 non-smoking participants have shown acute effects of exercise on cortisol (Jacks et al., 2002; McGuigan et al., 2003; Pomerleau et al., 1987). Conservatively, we therefore sought to examine the effects of exercise with 18 participants.


Design and procedure All participants initially attended a screening session to confirm smoking status, nicotine dependence using the Fagerstro¨m Test for Nicotine Dependence (FTND) (Heatherton, Kozlowski, Frecker, & Fagerstro¨m, 1991), and recent levels of exercise using the International Physical Activity Questionnaire (IPAQ) (Craig et al., 2003). Then, using a crossover design (Daniel et al., 2006; Taylor, Katomeri, & Ussher, 2005, 2006), participants attended three treatment sessions involving walking, running, and passive conditions, where condition order was assigned sequentially based on recruitment order. To control for diurnal variation in cortisol concentration within participants, each session was conducted on separate, non-consecutive days, at the same time of day. Participants maintained normal smoking behaviour before the screening session, and abstained for 3 h before each of the three treatment sessions. This is a shorter period of abstinence than typically reported in the literature and was chosen on the basis of findings from a pilot study we conducted, in which participants noted that longer periods of abstinence were a barrier to participation in such studies. However, in a recent review of exercise and smoking cessation studies, Taylor and colleagues concluded that length of abstinence and strength of baseline cravings do not appear to impact significantly on the effects of exercise (Taylor et al., 2007). Taylor and Katomeri (2006) observed post-exercise changes in cravings following only 2 h of abstinence. Additionally, research has reported a significant decline in cortisol after an absence of 4 h (Cohen, al’Absi, & Collins, 2004). Accordingly, a 3-h abstinence period was adopted in this study to facilitate participant recruitment. Smoking status was confirmed by both self-report and carbon monoxide testing, using the Micro 4 Smokerlyzer (Bedfont Scientific, USA). Three hours of abstinence from smoking was confirmed by testing for a reduction in exhaled carbon monoxide relative to screening condition values and to confirm a carbon monoxide cut-off of less than 10 parts per million (ppm). At the beginning of each treatment session (after temporary abstinence), we attempted to further

3

elevate cravings by briefly presenting unlit cigarettes to participants in all conditions, a procedure previously used to elicit cravings (Taylor & Katomeri, 2006). Each treatment session included one of three 15-min conditions: (1) sitting on a chair placed on the treadmill, (2) briskly walking (45–50% heart rate reserve) on a treadmill, or running (80– 85% heart rate reserve) on a treadmill, followed by a 30-min monitoring period. Calculated heart rate reserve was based on resting heart rates collected from each participant at screening, and age-predicted maximal heart rate. In the physically active treatment sessions, 2-min warm-up and cool-down periods were included to provide participants the time needed to reach the target heart rates of each session. Participants were verbally prompted to increase treadmill speed gradually, until the target heart rate had been reached, at which time the 15-min countdown for each exercise bout commenced. Throughout both exercise bouts, treadmill speed was increased and reduced as required to maintain target heart rates. Cravings and heart rate were assessed at baseline, mid-condition, and 0, 10, 20, and 30 min after each treatment. Ratings of perceived exertion (RPE) (Borg, 1998) were assessed throughout both active treatments. Cortisol was assessed in the screening session, and three times during each treatment session (baseline, immediately after, and 30 min after each treatment). Measures Cravings were assessed using two items and a 7item Likert-like scale: ‘‘I have a desire to smoke right now’’ (1 ¼ strongly agree; 7 ¼ strongly disagree) and ‘‘the strength of my desire to smoke right now is’’ (1 ¼ very strong; 7 ¼ very weak) (Tiffany & Drobes, 1991; West & Russell, 1985). Heart rate was monitored continuously using Polar 810i heart rate monitors and chest straps. Saliva samples were collected for analysis of salivary cortisol concentration. Samples were immediately frozen (7208C) until analysis. Analysis was performed using the Salimetrics Salivary Cortisol Immunoassay Kit (Salimetrics Catalogue No. 13002/1-3012), a competitive immunoassay specifically designed for the quantitative measurement of salivary cortisol. Statistical analyses One-way analyses of variance (ANOVAs) were conducted to identify potential order effects on the main outcomes. One-way ANOVAs were also used to compare baseline craving scores and cortisol concentration across treatment conditions. As a manipulation check, one-way ANOVAs were conducted to


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compare mean mid-condition heart rate during the three treatments. An overall repeated-measures two-way ANOVA [treatment (three levels: passive, walking, and running conditions) 6 time (six levels: pre-condition, mid-condition, 0, 10, 20, and 30 min postcondition)] was used to identify interaction and main effects and trends for measures of cravings (desire and strength of desire to smoke), and similarly for cortisol but with time as three levels (pre-condition, and 0 and 30 min post-condition). We examined linear and quadratic trends, since exercise has previously been shown to initially reduce cravings, followed by a return to baseline after exercise, whereas cravings remain fairly constant during and after a passive condition. Violations of the assumption of sphericity were corrected using GreenhouseGeisser estimates (e). Post hoc planned comparisons of baseline desire to smoke, strength of desire to smoke ratings, and cortisol concentrations, against all subsequent measurement points (i.e. baseline desire to smoke vs. mid-intervention, and 0, 10, 20, and 30min post-intervention), were conducted through a series of condition 6 time ANOVAs. At each instant after baseline, analyses of covariance (ANCOVAs) were performed to identify differences between conditions, controlling for baseline values, for each outcome (see Vickers & Altman, 2001). Additionally, ANCOVAs were performed to examine the potential moderating effects of sex, nicotine dependence (Fagerstro¨m Test for Nicotine Dependence), and physical activity levels (accumulated number of minutes of moderate and vigorous exercise, collected through the International Physical Activity Questionnaire). Bonferroni corrections (P 5 0.01) were used on all dependent variables. Results Twenty-six respondents were initially screened and 18 participants were randomized into the study. Eight individuals did not participate due to lack of time or interest after screening for eligibility. The 18 participants (10 males, 8 females) had the following mean characteristics: age, 26.0 years (s ¼ 4.2); body mass index, 23.0 (s ¼ 3.2); mean cigarettes per day, 13.9 (s ¼ 3.6); Fagerstro¨m Test for Nicotine Dependence, 4.4 (s ¼ 1.7), indicating moderate to high levels of nicotine dependence; physical activity, 171 min (s ¼ 165) of moderate and/or vigorous physical activity each week; carbon monoxide (at screening, pre-abstinence), 10.8 ppm (s ¼ 11.5); carbon monoxide (after abstinence at each treatment session), 8.6 ppm (s ¼ 8.6) [carbon monoxide treatment values were consistently found to be lower than carbon monoxide screening scores (withinparticipant comparison)]; and treatment condition

self-reported time of last cigarette, 297.7 min (s ¼ 250.3). One-way ANOVAs failed to detect any significant differences in baseline desire to smoke, strength of desire to smoke, or salivary cortisol concentrations, between test conditions, and there was no effect of order on baseline values. Manipulation check Mean mid-condition heart rate values of 71.0% (s ¼ 4.7) heart rate reserve, 47.4% (s ¼ 7.0) heart rate reserve, and 81.5% (s ¼ 5.4) heart rate reserve were recorded during the passive, walking, and running condition, respectively. Mid-walk 89% of participants had heart rates between 45 and 50% heart rate reserve, and mid-run 78% of participants had heart rates within the prescribed 80–85% range. The remaining participants were all within 8 beats min71 below these ranges. While no significant differences in heart rate were found between baseline and subsequent time points during the passive condition, heart rate in the walking and running conditions was significantly elevated above that in the passive condition (P 5 0.001), and heart rate in the running condition was higher than that in the walking condition (P 5 0.001). Furthermore, ratings of perceived exertion ranged from 11 to 16 (mean 13.4, s ¼ 1.2) during the brisk walking condition and from 13 to 18 (mean 16.2, s ¼ 1.4) during the running condition, indicating somewhat challenging and heavy/very heavy exertion. Rating of perceived exertion, between pre- and mid-condition, was significantly higher during running than walking. Cravings A condition (3) 6 time (6) effect of F3.96,67.4 ¼ 6.428 (P 5 0.001, e ¼ 0.49, partial Z2 of 0.304) was observed for desire to smoke. Quadratic (F1,17 ¼ 7.638, P 5 0.05, partial Z2 of 0.310) and cubic (F1,17 ¼ 18.610, P 5 0.001, partial Z2 of 0.523) condition (2) 6 time (6) trends were found between the passive and walking conditions. Quadratic (F1,17 ¼ 33.396, P 5 0.001, partial Z2 of 0.663) and cubic (F1,17 ¼ 23.313, P 5 0.001, partial Z2 of 0.578) condition (2) 6 time (6) trends were also found between the running and passive conditions. No significant interaction was observed between the walking and running conditions for desire to smoke. Table I shows that running (compared with the passive condition) reduced desire to smoke for up to 20 min post-treatment, while walking reduced it until 10 min post-treatment. Analyses of covariance also showed that, when controlling for baseline, desire to smoke was lower in the walking condition, compared with the passive condition, at the mid-

Exercise intensity and cravings to smoke

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Table I. Results of post hoc planned comparisons between baseline and all subsequent time points, by test session. F

P

Partial Z2

mid-condition 0 min 10 min 20 min 30 min

23.710 16.399 6.697 0.385 4.401

0.000*** 0.001*** 0.021* 0.544 0.053

0.613 0.522 0.309 0.205 0.227

Passive vs. running condition


21.429 34.282 11.498 6.000 3.985

0.000*** 0.000*** 0.004** 0.027* 0.064

0.588 0.696 0.434 0.286 0.210

Walking vs. running condition


1.206 1.709 1.206 6.429 0.160

0.289 0.211 0.289 0.023* 0.900

0.074 0.102 0.074 0.300 0.001


8.915 8.145 1.547 0.014 0.245

0.009** 0.012* 0.233 0.907 0.628

0.373 0.352 0.093 0.001 0.016

Passive vs. running condition


13.069 11.498 5.435 0.968 0.595

0.003** 0.004** 0.034* 0.341 0.453

0.466 0.434 0.266 0.061 0.038

Walking vs. running condition


0.146 0.211 1.644 2.304 0.277

0.708 0.652 0.219 0.150 0.606

0.010 0.014 0.099 0.133 0.018

0 min 30 min 0 min 30 min 0 min 30 min

9.864 0.390 0.040 1.251 1.767 4.586

0.008** 0.543 0.845 0.284 0.207 0.052

0.431 0.029 0.003 0.088 0.120 0.261

Variable


Desire to smoke (n ¼ 18) Passive vs. walking condition

Strength of desire to smoke (n ¼ 18) Passive vs. walking condition

Salivary cortisol concentrations (n ¼ 14) Passive vs. walking condition Passive vs. running condition Walking vs. running condition

***P 5 0.001; **P 5 0.01; *P 5 0.05.

point, immediately after, and 30 min after treatment. The running condition produced lower scores, compared with the passive condition, at up to 10 min post-treatment, and at 20 min post-treatment compared with the walking condition. A condition (3) 6 time (6) effect of F4.76, 81.02 ¼ 4.682 (P ¼ 0.001, e ¼ 0.477, partial Z2 of 0.216) was observed for strength of desire to smoke (see Figure 1). Both quadratic (F1,17 ¼ 5.919, P 5 0.05, partial Z2 of 0.258) and cubic (F1,17 ¼ 12.987, P 5 0.01, partial Z2 of 0.433) condition (2) 6 time (6) trends were identified between the passive and walking conditions, and between the running and passive conditions (quadratic: F1,17 ¼ 16.994, P 5 0.001, partial Z2 of 0.500; cubic: F1,17 ¼ 20.425, P 5 0.001, partial Z2 of 0.546). No significant interaction was observed between walking and

running for strength of desire to smoke. Table I shows that running (compared with the passive condition) reduced the desire to smoke for up to 10 min post-treatment, whereas walking reduced it until immediately post-treatment. Analyses of covariance also showed that, when controlling for baseline, strength of desire to smoke was lower in the walking condition than in the passive condition, at the midpoint and immediately after treatment. The running condition produced lower scores than the passive condition at up to 20 min post-treatment. Salivary cortisol Of the 18 participants who completed the study protocol, four sets of saliva samples were excluded from analysis after one or more samples were found to


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Figure 1. Strength of desire to smoke scores at each time point (n ¼ 18; mean and standard error).

Figure 2. Salivary cortisol concentration (mg dl71) (n ¼ 14; mean and standard error).

be contaminated with blood. Accordingly, 14 sets of saliva samples were analysed. Salivary cortisol was analysed using an ELISA method (Salimetrics, State College, PA). The sensitivity of the assay was 0.03 mg dl71. The intra-assay coefficient of variation for low (0.097 mg dl71) and high (0.999 mg dl71) level controls was 3.65 and 3.35% respectively, and the inter-assay coefficient of variation for low (0.106 mg dl71) and high (1.067 mg dl71) level controls was 5.40 and 4.17% respectively. Cortisol analysis was performed by the Women’s Health and Exercise Laboratory at the University of Toronto (Toronto, Canada). While no condition (3) 6 time (3) effects were found, a main effect of time (F1.09, 14.29 ¼ 5.465, P 5 0.05, partial Z2 of 0.296) was observed for salivary cortisol (see Figure 2). A quadratic condition (2) 6 time (3) trend was observed between the passive and walking conditions (F1,13 ¼ 4.573, P ¼ 0.05, e ¼ 0.463, partial Z2 of 0.260), and a linear condition (2) 6 time (3) trend was observed between walking and running (F1,13 ¼ 4.586, P ¼ 0.05, e ¼ 0.463, partial Z2 of 0.261). Table II shows that there was a significant reduction in cortisol in response to walking (compared with the passive condition) between baseline and the end of treatment (F1,13 ¼ 9.864, P 5 0.01, partial Z2 of 0.4310, and there was a trend for walking to result in a greater reduction in cortisol (compared with running) at 30 min post-treatment (F1,13 ¼ 4.586, P 5 0.05, partial Z2 of 0.261) (see Figure 2). The ANCOVAs showed that, when controlling for baseline, cortisol was: lower in the walking condition compared with the running condition immediately after and 30 min after treatment; lower in the passive condition compared with the running condition immediately after treatment; and higher in the passive condition compared with the walking condi-

tion immediately after treatment. To identify any relationships between changes in salivary cortisol concentration and changes in cravings, both Pearson and Spearman correlations were conducted. No significant relationships were identified (analysis not reported here). Moderators and between-participant factors Sex, physical activity levels (accumulated minutes of moderate and vigorous physical activity participation), time since last cigarette, and Fagerstro¨m Test for Nicotine Dependence scores were not identified as significant between-participant factors or covariates among the cravings variables or cortisol concentration values. Discussion While acute bouts of moderate-intensity physical activity have consistently been shown to decrease cigarette cravings in temporarily abstinent smokers (Taylor et al., 2007), prior to the current study, only one adequately controlled study had investigated the impact of acute high-intensity exercise (cycle ergometry) on cravings. Also, the mechanisms underlying this exercise-mediated reduction in cravings – particularly physiological mechanisms – were unknown. The current study differs from that of Everson and colleagues (2008) in terms of mode (running/walking vs. cycling), exercise duration (15 min vs. 10 min), duration of abstinence (3–4 h vs. overnight abstinence), additional pre-experimental cue-elicitation in the present study, and the examination of cortisol as a possible mechanistic factor. Consistent with the findings reported by Everson et al. (2008), vigorous exercise generally had a similar effect to moderate exercise in terms of the magnitude of craving

Exercise intensity and cravings to smoke

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Table II. Heart rate, cravings variables, and salivary cortisol concentration, by test session and over time (means and standard deviations).

Variable

Session

Heart rate (n ¼ 18)

Passive Walking Running Passive Walking Running Passive

Desire to smoke (n ¼ 18) Strength of desire to smoke (n ¼ 18)


Salivary cortisol concentration (n ¼ 14)

Baseline 80.8 76.6 82.2 5.4 5.3 5.3 5.8

(8.17) (11.57) (8.19) (1.58) (1.49) (1.45) (1.17)

Walking Running Screening

5.3 (1.50) 5.4 (1.29) 0.174 (0.0930)

Passive Walking Running

0.162 (0.0904) 0.174 (0.0784) 0.174 (0.0817)

Midcondition 79.6 132.6 170.0 4.9 3.1 2.6 4.9

(8.82)8{ (8.49)*8{ (7.98)*{{ (1.23)8{ (1.70)*8{ (1.79)*{{ (1.16)8{

3.1 (1.89)*{ 2.6 (1.94)*{

0 min posttreatment 77.4 93.6 108.6 5.2 3.4 3.1 5.2

(8.55)8{ (13.40)*8{ (12.05)*{{ (1.29)8{ (1.65)*{ (1.66)*{ (1.31)8{

3.3 (1.56)*{ 3.0 (1.88)*{


(9.40)8{ (9.61)8{ (10.02)*{{ (1.41)8 (1.58) (1.72)*{ (1.46)8

3.9 (1.64) 3.3 (1.75)*{

0.147 (0.0745){8 0.136 (0.0553)*{8 0.164 (0.0975){{


(8.51)8{ (9.83)8{ (9.75)*{{ (1.26) (1.20)8 (1.84){ (1.41)8

4.6 (1.42) 4.1 (1.80)*{


(9.94)8{ (9.99)8{ (10.79)*{{ (1.34){ (1.37){ (1.96) (1.24)

4.8 (1.31) 4.5 (1.93)

0.113 (0.0461) 0.114 (0.0598)*8 0.163 (0.1298){

*Significantly different from baseline, same condition (P 5 0.05). {Significantly different from same time point, walking condition (P 5 0.05). {Significantly different from same time point, passive condition (P 5 0.05). 8Significantly different from same time point, running condition (P 5 0.05).

reduction during exercise. However, in our study the effects on both craving measures lasted longer following high-intensity exercise than moderateintensity exercise, remaining significantly reduced below control group values for up to ten additional minutes post-treatment. Only at 30 min post-exercise had walking reduced the desire to smoke, compared with the passive condition, whereas running had no such effect. The same was not true for the strength of desire to smoke measure, suggesting the need to replicate this finding, although a similar duration of effects of walking has also been reported (Taylor & Katomeri, 2007). Cortisol as a mechanism While 15-min bouts of brisk walking and running resulted in similar reductions in cravings, the changes in salivary cortisol concentration were different. Cortisol declined in both the passive and walking conditions and this effect was attenuated in the vigorous condition as hypothesized. The absence of any significant relationships between changes in salivary cortisol concentration and changes in cravings, yet parallel reductions in cravings from both moderate and vigorous exercise, suggests that cortisol may not be a central mechanism, although it cannot be discounted based on this evidence. It may be that different mechanisms operate at different intensities (Faulkner & Carless, 2006). Additionally, the attenuation of cortisol reductions in the running condition might explain the extended reduction in cravings compared with the walking condition. At the least, this study has demonstrated that a 15-min bout of high-intensity exercise is sufficient to induce changes in cortisol concentration in 3-h abstinent

smokers – a novel finding in itself, as much longer bouts of activity are required to effect such change among non-smokers. Further studies are necessary to explore this interaction of acute exercise and cortisol activity during nicotine withdrawal and its implications for overall health. Incorporation of greater periods of abstinence, and investigation during quit attempts, may also make the effects more evident, as greater abstinence-induced declines in cortisol concentration will have manifested (al’Absi et al., 2004; Rasmusson et al., 2006; Steptoe & Ussher, 2006; Ussher et al., 2006b), although research has reported a significant decline in cortisol, relative to pre-smoking abstinence levels, after abstinence of 4 h (Cohen et al., 2004). Future research could strengthen the exploration of cortisol as a mechanism by establishing a baseline that collects saliva six times during a 25-h period of smoking (Yehuda et al., 2003). Exercise intensity In general, cravings were reduced during both walking and running conditions, relative to passive controls, but repeated-measures ANOVAs failed to identify any significant interactions between the two exercise intensities. This may suggest the presence of a ceiling or threshold effect of exercise intensity rather than a dose–response effect: a requisite exercise intensity must be reached to achieve maximal reductions in cravings, but beyond that intensity little additional benefit is gained, relative to the added exertion. The longer duration of effects of the running treatment compared with the walking treatment (desire to smoke and strength of desire to smoke remained reduced below passive condition

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values for 20 min post-run) is a potential finding of interest. Such differences were not found by Everson et al. (2008), maybe due to the different mode (running) and/or longer exercise duration (15 min) in the current study. While the clinical significance of this small effect of exercise intensity on duration of cravings reduction, if any, is unclear, these findings clearly demonstrate that high-intensity exercise does not elevate nicotine cravings in smokers experiencing withdrawal, a concern previously noted in the literature (Taylor & Ussher, 2005). Therefore, exercise-based smoking cessation advice may now be better tailored to meet the demands of the individual attempting to quit – participation in either vigorous exercise or moderate physical activity will provide generally similar reductions in cravings. Limitations The current study had some limitations that should be addressed in future research. First, future research should use a longer period of abstinence. Participants’ required abstinence was only 3 h, rather than the typical 12–15 h (overnight) abstinence of other studies to date (with the exception of Taylor & Katomeri, 2006). This length of abstinence may have limited the changes in salivary cortisol concentration. A positive implication is that comparable postexercise reductions in cravings were reported here as in studies with longer periods of abstinence. Furthermore, the sample in the present study exhibited the second highest Fagerstro¨m Test for Nicotine Dependence scores when compared with the acute exercise studies assessed by Taylor and colleagues (2007), indicating that reduced periods of abstinence may facilitate the recruitment of more nicotine-dependent or ‘‘hardcore’’ smokers than longer abstinence protocols. This has important implications for future researchers in designing craving-related studies and who are purposefully sampling smokers with greater nicotine dependency. Second, the impact of bouts of exercise on smoking behaviour is not clear. Incorporation of ad libitum smoking measures, such as number of cigarettes consumed in a day, time taken (after test session) before smoking the first cigarette, or the amount of nicotine inhaled, should be considered for future investigation. For example, Taylor and Katomeri (2007) found delays in ad libitum smoking following acute exercise after a period of abstinence. Research such as this is needed to increase ecological validity and to demonstrate that such laboartory post-exercise effects of cravings are observed in natural settings, and these reductions do help to facilitate attempts to quit. Third, there may have been a selection bias in that participants self-reported relatively high levels of

engagement in moderate to vigorous physical activity. Seven participants were meeting or exceeding current guidelines of 30 min per day of at least moderate physical activity most days of the week. The findings may not be generalizeable to sedentary smokers who may experience short bouts of moderate exercise, but particularly vigorous exercise, differently to more active smokers. For example, physically active individuals can demonstrate attenuated cortisol responses to acute exercise compared with inactive individuals (Rudolph & McAuley, 1998). Although physical activity was not a significant covariate among the cravings variables or cortisol concentration values, future research investigating cortisol in this context could focus on ‘‘inactive’’ participants (e.g. exercise on three or fewer days a week, for 30 min per day; Everson et al., 2008) given that smokers tend to be less active than non-smokers (Kaczynski, Manske, Mannell, & Grewal, 2008). Conclusions Within a laboratory setting, acute bouts of both moderate and vigorous exercise reduce craving scores for 10–30 min post-exercise in temporarily abstinent smokers. Research is still needed to further our understanding of the potentially causal mechanisms responsible for post-exercise reductions in cravings. Given that moderate exercise may be easier to adopt and maintain than vigorous exercise for sedentary smokers (Everson et al., 2008), enough is currently known about acute exercise and reduction of cravings to confidently prescribe moderate exercise as an evidence-based strategy for dealing with cravings and withdrawal symptoms.

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