Associations of physical activity and depression: Results from the Irish Longitudinal Study on Ageing.

Physical activity (PA) can protect against depression, but few studies have assessed whether meeting PA guidelines is sufficient, or if benefits can be derived from greater volumes of PA. The present study examines cross-sectional and prospective associations between different volumes of moderate-to-vigorous PA (MVPA) and walking, and depressive symptoms and status. Participants (n = 4556; 56.7% female) aged ≥ 50 years completed the International PA Questionnaire (IPAQ) at baseline and the Center for Epidemiological Studies Depression Scale at baseline and two years later. Prevalence and incidence of depression were 9.0% (n = 410) and 5.0% (n = 207), respectively. After full adjustment, odds of prevalent depression were: 40% (OR = 0.60, 95%CI: 0.48-0.76) lower among those meeting PA guidelines; 23% (OR = 0.77, 0.49-1.21) and 43% (OR = 0.57, 0.45-0.73) lower among those in moderate and high categories, respectively; and, 22% (OR = 0.78, 0.61-1.01) and 44.0% (OR = 0.56, 0.42-0.74) lower among those in moderate and high walking tertiles, respectively. Odds of incident depression were: 23% (OR = 0.77, 0.58-1.04) lower among those meeting PA guidelines; 37% (OR = 0.63, 0.32-1.22) and 20.0% (OR = 0.80, 0.59-1.09) lower among those in moderate and high categories, respectively; and, 21% (OR = 0.79, 0.56-1.12) and 25% (OR = 0.75, 0.52-1.07) lower among those in moderate and high walking tertiles, respectively. Moderate and high volumes of MVPA were significantly associated with lower odds of concurrent depression, and significantly and non-significantly associated with reduced odds of incident depression, respectively. Meeting recommended levels of MVPA and walking were associated with significantly lower odds of concurrent depression, and non-significantly reduced odds of the development of depression over two years.

Assessing sustainability of Lifestyle Education for Activity Program (LEAP).

Sustained intervention effects are needed for positive health impacts in populations; however, few published examples illustrate methods for assessing sustainability in health promotion programs. This paper describes the methods for assessing sustainability of the Lifestyle Education for Activity Program (LEAP). LEAP was a comprehensive school-based intervention that targeted change in instructional practices and the school environment to promote physical activity (PA) in high school girls. Previous reports indicated that significantly more girls in the intervention compared with control schools reported engaging in vigorous PA, and positive long-term effects on vigorous PA also were observed for girls in schools that most fully implemented and maintained the intervention 3 years following the active intervention. In this paper, the seven steps used to assess sustainability in LEAP are presented; these steps provide a model for assessing sustainability in health promotion programs in other settings. Unique features of the LEAP sustainability model include assessing sustainability of changes in instructional practices and the environment, basing assessment on an essential element framework that defined complete and acceptable delivery at the beginning of the project, using multiple data sources to assess sustainability, and assessing implementation longitudinally.

Chronic activity wheel running reduces the severity of kainic acid-induced seizures in the rat: possible role of galanin.

Studies in both humans and rodents suggest that exercise can be neuroprotective, but the mechanisms by which this occurs are still poorly understood. Three weeks of voluntary, physical activity in rats upregulates prepro-galanin messenger RNA levels in the locus coeruleus. Galanin is a neuropeptide extensively coexisting with norepinephrine that decreases neuronal hyperexcitability both in vivo and in vitro. Thus, exercise may diminish neural hyperexcitability through a galaninergic mechanism. The current experiments tested whether voluntary activity wheel running would protect against kainic acid-evoked seizures and whether galaninergic signaling is a necessary factor in this protection. In experiment 1, rats were given access to running wheels or remained sedentary for three weeks. After this period, rats received an intraperitoneal (i.p.) injection of 0, 7, 10 or 14 mg/kg kainic acid. Exercise decreased the severity of or eliminated seizure behaviors and hippocampal c-fos expression induced by kainic acid. In experiment 2, exercising or sedentary rats were injected intracerebroventricularly (i.c.v.) with 0.2 or 0.4 microg of kainic acid following either an injection of M-40 (a galanin receptor antagonist) or saline. Exercise decreased kainic acid-induced seizures at the 0.2 microg dose, and M-40 (6 nmol) decreased this effect. In contrast, there were no detectable differences between exercising and sedentary rats in behavior at the 0.4 microg dose. The results suggest that the protective effects of exercise against seizures are at least partially mediated by regulation of neural excitability through a process involving galanin.

Factorial invariance and latent mean structure of questionnaires measuring social-cognitive determinants of physical activity among black and white adolescent girls.

BACKGROUND: We previously developed questionnaires based on contemporary theories to measure physical activity determinants among youth [Motl et al., Prev Med 2000; 31:584-94]. The present study examined the factorial invariance and latent mean structure of unidimensional models fit to the questionnaires measuring attitude, subjective norm, perceived behavioral control, and self-efficacy about physical activity among black and white adolescent girls. METHODS: Black (n = 896) and white (n = 823) girls in the 8th grade completed the questionnaires measuring attitude, subjective norm, perceived behavioral control, and self-efficacy about physical activity. The responses were subjected to analyses of factorial invariance and latent mean structure using confirmatory factor analysis with full-information maximum likelihood estimation in AMOS 4.0. RESULTS: The unidimensional models of the four questionnaires generally demonstrated invariance of the factor structure, factor loadings, and factor variance across race but not invariance of the variance-covariance matrices or item uniquenesses. The analyses of latent mean structure demonstrated that white girls had higher latent mean scores on the measures of attitude and self-efficacy than black girls; there were similar, but smaller, differences between white and black girls on the measures of subjective norm and perceived behavioral control. CONCLUSIONS: The questionnaires can be employed in interventions to test the mediating influences of attitude, subjective norm, perceived behavioral control, and self-efficacy on participation in physical activity by black and white adolescent girls.

Measuring enjoyment of physical activity in adolescent girls.

BACKGROUND: Enjoyment has been implicated as a determinant of physical activity among youth, but advances in understanding its importance have been limited by the use of measures that were not adequately validated. The present study examined: (1) the factorial validity of the Physical Activity Enjoyment Scale (PACES), and (2) the construct validity of PACES scores. METHODS: Adolescent girls (N=1797), who were randomly assigned to calibration (n=899) and cross-validation (n=898) samples, completed the PACES and measures of factors influencing enjoyment of physical education, physical activity, and sport involvement. The factorial validity of the PACES and the measure of factors influencing enjoyment of physical education was tested using exploratory and confirmatory factor analysis. The hypothesized relationships among the measures were tested using structural equation modeling. RESULTS: Unidimensional models fit the PACES and the measure of factors influencing enjoyment of physical education in the calibration and cross-validation samples. The hypothesized relationships between the PACES and the measures of factors influencing enjoyment of physical education, physical activity, and sport involvement were supported in the entire sample, were similar in African-American and Caucasian girls, and were independent of physical fitness. CONCLUSIONS: Evidence of factorial validity and convergent evidence for construct validity indicate that the PACES is a valid measure of physical activity enjoyment among adolescent girls, suitable for use as a mediator variable in interventions designed to increase physical activity.

Perceived exertion during incremental cycling is not influenced by the Type A behavior pattern.

Recent publications have perpetuated a concern that the Type A Behavior Pattern (TABP) influences ratings of perceived exertion (RPE) during exercise testing. Previous studies of this topic used the Jenkins Activity Survey (JAS) which lacks validity for predicting the criterion Structured Interview (SI) for TABP and used exercise protocols that were unstandardized or yielded results that were uninterpretable for clinical exercise prescription. We used the SI to classify 44 normotensive men (18-35 y) according to TABP and compared their RPE during an incremental cycling test to peak oxygen uptake (VO2peak). Groups did not differ on maximal test performance or RPE at any stage of the test, even after adjusting RPE for small group variations in % VO2peak and ventilatory equivalent for oxygen, which are strong correlates of RPE during incremental exercise. The findings agree with our prior report [14] that no relationship existed between RPE and several self-report measures of TABP. We conclude that there is no empirical basis for the view that the Type A Behavior Pattern affects cycling performance or ratings of perceived exertion during standard exercise testing in young white men.

Acoustic startle eyeblink response after acute exercise.

The acoustic startle eyeblink response (ASER) is a useful probe for investigating central nervous system activity associated with emotional responses to aversive and appetitive stimuli. Though the ASER is sensitive to change in emotional arousal, the effect of acute physical exertion on ASER has not been reported. We examined changes in ASER amplitude and latency in 26 healthy young men (24+/-5 yr) after 20 min of cycling at light and hard intensities (40% and 75% VO2peak) and after 20 min of quiet rest. Mixed model ANCOVA, controlling precondition scores, indicated no effects for ASER amplitude or latency in either sedentary or active participants (p>.10). Our findings indicate that possible effects of acute exercise on potentiated startle or ASER responses elicited by positive or negative foreground stimuli should not be expected to be confounded by an altered baseline acoustic startle eyeblink response when measured in healthy young men.

Prepro-galanin messenger RNA levels are increased in rat locus coeruleus after treadmill exercise training.

The effects of treadmill exercise training on prepro-galanin (GAL) and tyrosine hydroxylase (TH) gene expression in the locus coeruleus (LC) were examined. Male Fischer-344 rats (n=9) were assigned to 6 weeks of treadmill running. An additional group of animals comprised the sedentary home cage control group (n=9). Levels of GAL and TH messenger RNA (mRNA) in the LC were measured using in situ hybridization histochemistry with autoradiography. Levels of GAL mRNA were higher in treadmill trained animals compared to sedentary animals, but there was no effect of treadmill running on TH mRNA. These results suggest that gene expression for galanin is responsive to repeated exercise stress and may have a neuromodulatory role in LC-noradrenergic adaptation to treadmill exercise training.

Factorial validity and invariance of questionnaires measuring social-cognitive determinants of physical activity among adolescent girls.

BACKGROUND: There are few theoretically derived questionnaires of physical activity determinants among youth, and the existing questionnaires have not been subjected to tests of factorial validity and invariance. The present study employed confirmatory factor analysis (CFA) to test the factorial validity and invariance of questionnaires designed to be unidimensional measures of attitudes, subjective norms, perceived behavioral control, and self-efficacy about physical activity. METHODS: Adolescent girls in eighth grade from two cohorts (N = 955 and 1,797) completed the questionnaires at baseline; participants from cohort 1 (N = 845) also completed the questionnaires in ninth grade (i.e., 1-year follow-up). Factorial validity and invariance were tested using CFA with full-information maximum likelihood estimation in AMOS 4.0. Initially, baseline data from cohort 1 were employed to test the fit and, when necessary, to modify the unidimensional models. The models were cross-validated using a multigroup analysis of factorial invariance on baseline data from cohorts 1 and 2. The models then were subjected to a longitudinal analysis of factorial invariance using baseline and follow-up data from cohort 1. RESULTS: The CFAs supported the fit of unidimensional models to the four questionnaires, and the models were cross-validated, as indicated by evidence of multigroup factorial invariance. The models also possessed evidence of longitudinal factorial invariance. CONCLUSIONS: Evidence was provided for the factorial validity and the invariance of the questionnaires designed to be unidimensional measures of attitudes, subjective norms, perceived behavioral control, and self-efficacy about physical activity among adolescent girls.

Failure of neonatal clomipramine treatment to alter forced swim immobility: chronic treadmill or activity-wheel running and imipramine.

We examined whether chronic running on a treadmill or activity wheel would attenuate the increased swim immobility that has been reported after neonatal clomipramine (CLI) treatment. Male Sprague-Dawley pups (N = 60) were injected with the monoamine reuptake inhibitor clomipramine hydrochloride (40 mg/kg per day i.p.) from 8 to 21 days of age. Another group (N = 12) received saline vehicle. At age 4 weeks, the CLI pups were randomly assigned to experimental conditions: (1) sedentary; (2) 24-h access to an activity wheel; (3) sedentary that received the antidepressant drug imipramine hydrochloride (10 mg/kg twice daily) during the last 10 days of the experiment; (4) activity wheel + imipramine; (5) treadmill running (30 m/min for 1 h at 0 degrees incline, 6 days/week). At age 16 weeks, rats underwent the Porsolt swim test 48 h after the last imipramine injection and/or the last exercise session. The increase in swim immobility among CLI-treated rats was small (one quarter of SD) and not statistically significant (p>0.10). The results are not consistent with our previous finding of antidepressant-like effects of activity-wheel running based on brain noradrenergic adaptations and enhanced male copulatory performance after neonatal CLI treatment. The lack of change in swim performance after clomipramine questions the generalizability of the CLI model of depression and the validity of the forced swim test as a behavioral measure of depression when it is used after neonatal CLI injection or chronic activity-wheel running.

Treadmill exercise training augments brain norepinephrine response to familiar and novel stress.

In a test of hypothalamic-pituitary-adrenal (HPA) cortical and hypothalamic-pituitary-gonadal (HPG) interaction during familiar and novel stress, we previously reported that treadmill exercise training led to blunted plasma adrenocorticotrophin (ACTH) response to acute treadmill running but a hyper-responsiveness of ACTH after novel immobilization. In this follow-up analysis, we examined whether those results might be plausibly explained by a similar effect of treadmill exercise training on increased levels of norepinephrine (NE) in hypothalamic and limbic brain regions which synergize to modulate the release of ACTH during stress. Ovariectomized Sprague-Dawley rats that had been exercise trained by treadmill running or remained sedentary for 6 weeks received intramuscular injections of estradiol benzoate (Eb) or sesame oil on each of 3 days prior to 15 min of familiar treadmill running or novel immobilization. Treadmill exercise training, regardless of Eb treatment or type of stress, increased NE levels in the paraventricular (PVN), arcuate, medial preoptic, and ventromedial areas of the hypothalamus and protected against depletion of NE in the locus coeruleus, amygdala, and hippocampus. We conclude that treadmill exercise training has a hyperadrenergic effect in brain areas that modulate hypothalamic regulation of ACTH release during stress that is independent of HPA-HPG interaction and novelty of the stressor. To help elucidate these findings, the effects of treadmill exercise training on A1-A2 nuclei which innervate the PVN and their relationship with the limbic and hypothalamic responses we report require study.

Treadmill exercise training blunts suppression of splenic natural killer cell cytolysis after footshock.

This study extended to treadmill exercise training our prior report (Dishman RK, Warren JM, Youngstedt SD, Yoo H, Bunnell BN, Mougey EH, Meyerhoff JL, Jaso-Friedmann L, and Evans DL. J Appl Physiol 78: 1547-1554, 1995) that activity wheel running abolished the suppression of footshock-induced natural killer (NK) cell cytolysis. Twenty-four male Fischer 344 rats were assigned to one of three groups (n = 8, all groups): 1) a home-cage control group, 2) a sedentary treatment group, or 3) a treadmill-running group (0 degrees incline, 25 m/min, 35 min/day, 6 days/wk). After 6 wk, the treadmill and sedentary groups received 2 days of footshock. Splenic NK cytotoxicity was determined by standard 4-h (51)Cr release assay. Percentages of lymphocytes were determined by flow cytometry. Plasma levels of ACTH, corticosterone, and prolactin concentration were measured by radioimmunoassay. After footshock, percentage of lysis relative to home-cage controls was 40% and 80% for sedentary and treadmill-trained animals, respectively (P < 0.05). Our results indicate that the protective effect of chronic exercise on innate cellular immunity in the Fischer 344 male rat is not restricted to activity wheel running, nor is it explained by elevations in basal NK activity, increased percentages of splenic NK and cytotoxic T cells, or increased plasma levels of ACTH, corticosterone, and prolactin.

Heart rate variability, trait anxiety, and perceived stress among physically fit men and women.

BACKGROUND: It is unclear from prior reports whether the relationships between self-ratings of anxiety or emotional stress and parasympathetic nervous system components of heart rate variability are independent of personality and cardiorespiratory fitness. We examined those relationships in a clinical setting prior to a standardized exercise test. METHODS AND RESULTS: Heart rate variability (HRV) was measured during 5 min of supine rest among 92 healthy men (N=52) and women (N=40) who had above-average cardiorespiratory fitness as indicated by peak oxygen uptake measured during grade-incremented treadmill exercise. HRV datasets were decomposed into low-frequency (LF; 0.05-0.15 Hz) and high-frequency (HF; 0.15-0.5 Hz) components using spectral analysis. Self-ratings of trait anxiety and perceived emotional stress during the past week were also assessed. CONCLUSIONS: There was an inverse relationship between perceived emotional stress during the past week and the normalized HF component of HRV (P=0.038). This indicates a lower cardiac vagal component of HRV among men and women who perceived more stress. That relationship was independent of age, gender, trait anxiety, and cardiorespiratory fitness. It was also independent of heart rate; mean arterial blood pressure; and respiration rate, factors which can influence HRV and might be elevated among people reporting anxiety and perceived stress. We conclude that vagal modulation of heart period appears to be sensitive to the recent experience of persistent emotional stress, regardless of a person's level of physical fitness and disposition toward experiencing anxiety.

The influence of acute exercise on sleep following high caffeine intake.

The purpose of this study was to examine the influence of vigorous acute exercise on nocturnal sleep that had been disrupted by high doses (1200 mg) of caffeine throughout the daytime. Eight moderately fit, young males with a history of moderate caffeine use completed four conditions in a within-subjects, counterbalanced design: 60 min of (i) cycling at 60% VO(2peak) or (ii) quiet rest following placebo consumption, (iii) cycling, or (iv) quiet rest following the consumption of a high dose of caffeine. Each condition was performed twice from 1615-1715 h and followed by all-night polysomnographic recording. Subjects consumed two blinded 200-mg capsules of either lactose placebo or caffeine upon awakening, at 1600 h, and 2 h before bedtime. State anxiety was assessed at bedtime. Criterion scores consisted of the mean data across the two days in each condition. Sleep data were analyzed using a condition (exercise versus quiet rest) by drug (caffeine versus placebo) repeated-measures ANOVA. Caffeine-elicited sleep disturbance that was less than previously reported. Exercise attenuated selected sleep disturbances to a small degree. In general, the effects of exercise on sleep were not greater following caffeine compared to placebo. Indeed, increases in slow-wave sleep after exercise were approximately 1/3 smaller following caffeine treatment compared to placebo.

Perceived submaximal force production in young adult males and females.

UNLABELLED: Clinical treatment in physical rehabilitation routinely uses perceived relative forces. PURPOSE: This study used psychophysical methods to quantify subjects' errors during submaximal muscular force production. METHODS: A sample of young adult (aged 23 +/- 3 yr) females (N = 60, 62 +/- 14 kg) and males (N = 50, 72 +/- 13 kg) performed a chest press on a hydraulic dynamometer with which they were unfamiliar. In four consecutive presses with a 2-min rest interval between each press, the subjects were asked to produce a force in the order of 25%, 50%, 75% of their maximal force, and a final maximal press. Pilot data (N = 10) indicated good reliability (r(xx) > 0.80) for the protocol. RESULTS: The rs between perceived force production and the desired production were 0.76 (P < 0.001) for males and 0.75 (P < 0.001) for females. The exponent for the power function between the perceived and desired forces was 1.12 for males and 1.03 for females. The total error ranged from 2.82 kg x m (males) to 1.22 kg x m (females). The rs and the logarithmic matching of perceived and desired force indicated a linear relationship that is consistent with Borg's range model, which has proposed that perceptual intensities of force for different people are approximately set equal at a subjective maximum. CONCLUSION: Many young healthy subjects can produce relative muscular forces with good accuracy. However, some subjects will provide very inaccurate forces that might affect outcomes in rehabilitation or physical training.

Activity-wheel running blunts suppression of splenic natural killer cell cytotoxicity after sympathectomy and footshock.

We used chemical sympathectomy by 6-hydroxydopamine (6-OHDA) to examine whether adaptation by the sympathetic nervous system (SNS) is a plausible explanation for our prior finding that activity-wheel running blunts the suppression of splenic natural killer cell cytotoxicity after footshock. Male Fischer rats were assigned to treatments using a group (activity wheel vs. sedentary)x treatment (6-OHDA vs. saline)x condition (footshock vs. no shock) design. After 5-6 weeks, rats were injected i.p. with saline or with 40, 80, and 80 mg/kg 6-OHDA on pre experimental days -5, -3, and -1. Half the rats received 6 min of random footshock during a 40-min period. Cytotoxicity was determined by standard 4-h 51Cr release assay. Sympathectomy reduced splenic [NE] by 72%. After 6-OHDA injection and footshock, percent lysis was 33% lower in sedentary rats compared with activity-wheel runners and home-cage controls, p=0.048. The results suggest that activity-wheel running leads to adaptations that offset an altered SNS modulation of splenic NK cell cytotoxicity in response to footshock.

Brain noradrenergic responses to footshock after chronic activity-wheel running.

Effects of physical activity on brain noradrenergic response to footshock were examined. Male Fischer 344 rats were randomly assigned to shoebox cages with (AW) or without (SED) 24-hr access to an activity wheel for 4-5 weeks. Extracellular levels of norepinephrine (NE) and 3,4-dihydroxyphenyl-acetic acid (DOPAC) in the brain frontal cortex were measured in 20-min samples of microdialysate taken during a 2-hr baseline, 40 min of scrambled footshock, and a 1-hr recovery. Levels of messenger RNA (mRNA) for tyrosine hydroxylase (TH), c-fos, and prepro-galanin in the locus coeruleus were measured by in situ hybridization histochemistry with autoradiographic analysis. NE levels were the same for SED and AW rats at baseline but were elevated in SED compared with AW during and after footshock. Levels of mRNA for TH and c-fos were elevated after footshock but did not differ between SED and AW. Our findings suggest that wheel running blunts NE release in the brain frontal cortex in response to footshock but does not influence expression of the gene that encodes TH in the locus coeruleus.

Worksite physical activity interventions.

BACKGROUND: National objectives for public health have targeted worksite as important settings for interventions to increase physical activity. However, expert reviews reveal no scientific consensus about the effectiveness of worksite interventions for increasing physical activity or fitness. METHODS: We judged the quantity and quality of existing evidence against scientific standards for the internal and external validity of the research design and the validity of measurements. Meta-analytic methods were used to quantify the size of effects expressed as Pearson correlation coefficients (r). Variation in effect was examined in relation to several features of the studies deemed important for implementing successful worksite interventions. Pre-experimental cohort studies were excluded because they are sensitive to secular trends in physical activity. RESULTS: Twenty-six studies involving nearly 9,000 subjects yielded 45 effects. The mean effect was heterogeneous and small, r = 0.11 (95% CI, -0.20 to 0.40), approximating 1/4 S.D., or an increase in binomial success rate from 50% to 56%. Although effects varied slightly according to some of the study features we examined, effects were heterogeneous within levels of these features. Hence, the moderating variables examined did not explain variation in the effects (P > 0.05). The exception was that effects were smaller in randomized studies compared with studies using quasi-experimental designs (P < 0.05). CONCLUSIONS: Our results indicate that the typical worksite intervention has yet to demonstrate a statistically significant increase in physical activity or fitness. The few studies that have used an exemplary sample, research design, and outcome measure have also yielded small or no effects. The generally poor scientific quality of the literature on this topic precludes the judgment that interventions at worksites cannot increase physical activity or fitness, but such an increase remains to be demonstrated by studies using valid research designs and measures.

Activity wheel running blunts increased plasma adrenocorticotrophin (ACTH) after footshock and cage-switch stress.

We examined whether chronic circadian physical activity attenuates hypothalamic-pituitary-adrenal hormone responses after footshock with or without cage-switch stress. Young (45 g) male Fischer 344 rats were randomly assigned to individual suspended home cages (HC) or cages with activity wheels (AW) (12 h:12 h light-dark photoperiod). After 6 weeks, each animal from a pair matched on mass (HC and AW) and average weekly running distance (AW) was randomly assigned to controllable or uncontrollable footshock on 2 days separated by 24 h. Half the animals were returned to the HC after the first day of shock, and half were switched to a new shoebox cage. One animal of each pair could end the shock for both rats by performing an FR-2 lever press. The yoked animal could not control the shock. After shock on Day 2, trunk blood was collected after decapitation. Plasma adrenocorticotrophin (ACTH), corticosterone, and prolactin were determined by radioimmunoassay. ANOVA for a 2 Group (AW vs. sedentary) x 2 Test (controllable vs. uncontrollable shock) x 2 Condition (HC vs. cage-switch) design indicated a Group x Test x Condition effect [F(1, 48) = 5.07, p = 0.03] and a Test main effect [F(1, 47) = 6.93, p = 0.01] for ACTH. ACTH was higher for sedentary animals after uncontrollable footshock under cage-switch conditions and higher after uncontrollable versus controllable footshock when averaged across groups and cage conditions. No effects were found for corticosterone or prolactin. Our results extend to activity wheel running prior findings of a cross-stressor attenuation in plasma [ACTH] in response to cage-switch after treadmill exercise training, though the cross-stressor effect was additive with footshock. Consistent with our prior reports, the cross-stressor effect of wheel running was not apparent after footshock administered under home-cage conditions.