There is considerable evidence supporting the view that habitual physical activity is associated with positive mental health. While a number of hypotheses have been proposed as the basis for this affective beneficence(16), compelling evidence in support of a causal link for this relationship is lacking (18). Furthermore, it is known that psychological improvements can occur following exercise interventions that do not result in physiological improvements; conversely, it has been shown that psychological gains do not occur at times despite the observation that aerobic power and other physiological factors improve significantly (14). Hence, the nature of this relationship is certainly not law-like, and there is also a paradox involving the juxtaposition of exercise on the one hand and psychological change on the other. It is well established, for example, that exercise programs characterized by high levels of intensity, duration, and frequency result in mood disturbances in a predictable, dose-response manner(17). This research involving “overtraining” has been based almost entirely on training programs in sports or experimental settings where exercise dose is regulated by a coach or investigator(6,17).
Despite methodological shortcomings (7) and a tendency for investigators to ignore behavioral artifacts (e.g., halo effect, Hawthorne effect, demand characteristics) (14), indirect evidence suggests that physical activity leads to improved mood states, and anecdotal reports suggest that habitual exercise can result in addiction or dependency(15,25). It has been proposed that the mood-enhancing effects of exercise result from the production of endorphins or alteration of opiate receptor occupancy, but this view is based almost entirely on small animal research (10). Christie and Chesher (5) report, for example, that physical dependence cannot only be produced in mice following chronic exercise but that the observed dependency is comparable to that observed with morphine dependence. That is, exercise deprivation leads to withdrawal symptoms (e.g., “wet dog” shakes) identical to those noted in morphine-addicted mice following deprivation of morphine.
Since evidence suggests that habitual physical activity is associated with improved psychological states, anecdotal reports suggest that humans can become addicted or dependent on regular exercise, and animal research demonstrates that physical dependency can be created with chronic exercise(5), it would seem reasonable to predict that habitual exercisers who abstain from regular exercise may experience mood disturbance. In other words, if exercise has positive mental health benefits, and if it can actually lead to a physical dependency, it follows that cessation of this regular activity would result in dysphoric states (e.g., increased anxiety, depression). Indeed, this is one form of evidence that is necessary in order to argue that a causal link exists between exercise and improved mood states.
Published research dealing directly or indirectly with the effects of exercise deprivation is limited. Furthermore, differences in dependent and independent variables across studies have produced a variety of results. For example, periods of deprivation from exercise ranging from 2 to 6 wk show sleep-pattern disturbance suggestive of increased anxiety(1), increases in somatic symptoms(19), total mood disturbance as measured by the Profile of Mood States (POMS) (2,4), increases in anxiety(19), elevated scores on the depression, anger, and confusion subscales of the POMS (4), and decreased scores on the vigor subscale of the POMS (2,4). Similar results have been reported following brief periods of exercise deprivation(e.g., 1 d) (24). Epidemiological research bearing on this general question is limited. However, Robbins and Joseph(21) evaluate deprivation sensations in a survey of 345 runners. The sensations most frequently reported by runners who missed a run or series of runs include restlessness, irritability, and general fatigue. These results are consistent with other anecdotal reports(15), as well as results from the available intervention studies (1,2,4,19,24).
Many of the results reported in previous studies are confounded by involuntary exercise deprivation due to injury (4), the use of invalidated instruments (1,19,21), inconsistent or inadequate statistical analysis (2), and lack of manipulation of the period of deprivation (21). Furthermore, earlier research fails to operationalize or quantify habitual exercise activity. Several investigators rely on participants who were exercising as few as 3 d·wk-1 (1,2,4,19). This is problematic when trying to assess short-term effects of exercise deprivation. Sachs and Pargman(22) postulate that changes due to withdrawal from physical activity should be observable after 24-36 h of deprivation. Hence, one would not anticipate psychological effects with a brief period of exercise deprivation since participants in these studies would customarily not exercise for periods of 24-48 h.
The primary purpose of this investigation was to evaluate the influence of 3 d of exercise deprivation on selected psychological variables. The investigation was conducted in an effort to overcome some of the pitfalls associated with earlier research in this area. First, since we were studying short-term effects, we used a nonexercise period of 3 d to quantify the impact of a brief period of interruption in regular exercise. Second, criteria for involvement in the study included regular exercise at least 6-7 d·wk-1 for a minimum of 45 min per session. We also have tried to quantify the habitual activity patterns of the study participants by estimating the total exercise MET completed annually. Third, we have relied on voluntary exercise cessation in healthy subjects to eliminate the confounding influence of injury in earlier research (4,21). Little (11) shows that injuries can lead to a“deprivation crisis” for individuals classified as “fitness neurotics” and that this crisis can be accompanied by mood disturbance. Fourth, we have used validated psychological scales for our assessments. Fifth, we made our assessments at the same time of day on every day since it is not clear that time of day has been controlled in earlier studies. Finally, we have attempted to minimize demand characteristics by not communicating expectancies to participants. Indeed, we did not have a directional hypothesis, and when participants asked what we expected to find in the study, we replied: “We really are not sure since the results of earlier work on exercise deprivation are mixed.”
Participants. Ten habitual exercisers (6 men and 4 women) with a mean age of 27.4 yr (SD = 4.5) participated in this study. Because we wanted to quantify the acute effects of a short-term period of exercise deprivation, we studied individuals who exercised on an almost daily basis. (A few days of exercise deprivation would be normal for people who exercised, for example, 3-5 d·wk-1). All participants met the exercise criteria of a minimum of 45 min·d-1, 6-7 d·wk-1. They regularly engaged in activities such as jogging (N = 10), cycling (N= 8), and swimming (N = 8). The mean activity level, over the last year, for these habitual exercisers was estimated to be 4595 total MET (SD = 1250). Participants were paid $50.00 for taking part in this 5-d study.
Instruments. During each laboratory visit the participants completed the Y1 and Y2 versions of the State-Trait Anxiety Inventory (STAI)(23), POMS (13), the Depression Adjective Checklist (DACL) (12), and a 24-h history questionnaire. The STAI is a well-established measure of state and trait anxiety that has been used extensively in exercise science studies. The POMS, also used commonly in exercise research, contains six subscales designed to measure tension (T), depression (D), anger (A), vigor (V), fatigue (F), and confusion (C). Also, the five negative measures of affect (T,D,A,F,C) can be summed, and the one positive measure (V) subtracted, to provide an overall measure of total mood disturbance (TMD). In this study a constant of 100 was added to the TMD to avoid negative scores (i.e., below zero). The“today” set was used for the POMS, and participants were instructed to respond in terms of “... how you have been feeling today.” The DACL contains a list of adjectives used to measure depression. The 24-h history questionnaire consisted of questions related to factors such as sleep patterns, physical health, exercise levels, and general state of well-being.
Procedure. Informed consent was obtained from each participant prior to the first laboratory visit, and the consent form and research protocol were approved in advance by the appropriate Institutional Review Board (IRB) at the University of Wisconsin-Madison. Participants were told that the study would last 5 consecutive days (Monday-Friday), and for three of those days (Tuesday-Thursday) they would be asked to abstain from their regular exercise routines. They were also requested to be as physically inactive as their daily routines would allow on those days when exercise was not performed. Participants who walked or cycled to and from work were provided with bus passes and parking facilities for the 3-d nonexercise period to minimize “lifestyle” exercise (3). Inspection of the 24-h histories collected each day revealed that they were relatively sedentary for the 3-d nonexercise period. They reported to the laboratory to complete the questionnaires on Monday and Friday as soon as possible (within 15-30 min) following their regular exercise time and also reported to the laboratory at the same time on those days when they did not exercise (e.g., Tuesday, Wednesday, and Thursday). They completed the questionnaires while alone in a quiet room free of distractions.
We chose a post-test-only design with repeated measures for several reasons. First, we wanted to compare the effects of exercise with the effects of no exercise, so we were not interested in documenting the acute effects of the exercise session by taking both pre- and post-exercise measurements. Extensive literature provides evidence of the anxiolytic effects of acute exercise (14). Second, it would be inappropriate to perform pre-test measurements on the days when exercise was not performed, because of the methodological problem involved in choosing what the participants would do between the pre-test and post-test. For example, there is evidence that even a session of quiet rest results in decreased anxiety(20). Third, we wanted to minimize the introduction of demand characteristics in habitual exercisers via pretest sensitization.
Data were analyzed with a one-way repeated measures analysis of variance(ANOVA) (26). When a significant main effect was found, pairwise comparisons were performed using the Fisher-Hayter procedure(9). The means, standard deviations, and F values are presented in Table 1 for each variable. Power analyses were performed for each variable. The minimum sample size ranged from 5 to 8 for the primary variables (TMD, tension/anxiety, depression), and power ranged from 0.90 to 0.99 for these same variables (8).
Total mood disturbance (POMS). Analysis of the total mood disturbance (TMD) data revealed a significant main effect for days(F(4,36) = 4.81, P < 0.05). This effect revealed increased mood disturbance during the period of exercise deprivation followed by improved mood when exercise was resumed at the end of the week. These data are summarized in Table 1 and depicted inFigure 1. Pairwise comparisons of the means revealed that TMD scores were significantly higher (P < 0.05) on Wednesday compared with Monday. TMD scores were also significantly higher (P< 0.05) on Wednesday compared with Friday, when exercise was resumed.
Tension (POMS) and state anxiety (STAI). There was also a significant main effect for days in the tension scores as measured by the POMS(F(4,36) = 6.03, P < 0.05). Pairwise comparisons of the tension scores revealed that the scores on Wednesday were significantly higher(P < 0.05) than on Monday, Thursday, and Friday. In addition, there was a significant main effect for days for state anxiety(F(4,36) = 6.19, P < 0.05). Pairwise comparisons revealed that scores on Monday were significantly lower (P < 0.05) than all three days when exercise was not performed. These changes in tension and state anxiety closely resembled those for total mood disturbance and, therefore, are not depicted graphically.
Depression (DACL and POMS). There was a significant main effect for days for depression, as measured by both the POMS (F(4,36) = 2.93, P < 0.05) and the DACL (F(4,36) = 4.60,P < 0.05). Pairwise comparisons showed that depression scores(POMS) were significantly higher (P < 0.05) on Wednesday than Friday. Pairwise comparisons showed that depression scores (DACL) were significantly higher (P < 0.05) on Wednesday than Monday and Friday. Depression scores, as measured by the POMS and DACL, followed a pattern similar to total mood disturbance and, therefore, are not depicted graphically.
Other Measures. The main effect for days was also significant for confusion (F(4,36) = 3.09, P < 0.05) and vigor(F(4,36) = 2.86, P < 0.05). Pairwise comparisons revealed that confusion scores were significantly higher (P < 0.05) on Wednesday than Friday, and vigor scores were significantly lower(P < 0.05) on Wednesday than Monday.
The main effect for days was not significant (P > 0.05) for the anger and fatigue subscales of the POMS, nor was it significant for trait anxiety. These measures did not change significantly across the week.
The principal finding of this investigation was a pattern of increasing mood disturbance during the period of exercise deprivation followed by improved mood when exercise was resumed at the end of the week. This pattern was strikingly similar for total mood disturbance (POMS), tension (POMS), and state anxiety (STAI), as well as depression measured by both the POMS and the DACL. In addition, confusion (POMS) increased and then decreased in a similar pattern, whereas vigor (POMS) decreased with exercise deprivation and then improved to baseline levels with resumption of exercise.
The participants experienced a partial recovery by the third day (Thursday) of exercise deprivation. Scores for state anxiety, tension, depression, and total mood disturbance all showed improvement. It is possible that habitual exercisers deprived of exercise do experience acute (e.g., within 24-48 h) mood shifts, but adaptation soon occurs so that affective measures return to baseline levels. Alternatively, it is possible that the improved mood on the third day of deprivation was the result of knowing that they would be able to resume exercise following the third day. Indeed, three of the 10 participants elected to resume exercise within 2 h of the final deprivation period, and all 10 of the exercisers had resumed exercise within 24 h. Another explanation could be that demand characteristics were operating, but this seems unlikely since it is unreasonable to maintain that all the participants surmised that improvement in mood was expected on Thursday. (The authors did not anticipate this pattern of results). Another explanation could be that the participants' own expectations influenced the results. This may be a plausible explanation for the initial mood disturbance on Tuesday and Wednesday but fails to account for the improvement in mood on Thursday.
Our findings agree with those of Thaxton (24), who reports increased depression after 1 d of exercise deprivation compared with a control group. Thaxton (24) also observes small but insignificant changes in tension and vigor in the treatment group compared with the control group. These findings are consistent with the changes observed after 1 d of exercise deprivation in this study. Thaxton(24) does not report data for anger and confusion.
Studies involving longer periods of deprivation from exercise also report increased anxiety and depression (4,19), and changes in some POMS factors (2,4). However, the deprivation periods in these studies ranged from 2 to 6 wk(2,4,19), and the results of one study are confounded by injury (4). In addition, the participants exercised a minimum of 3 d·wk-1 in all three of these studies in contrast to the 6-7 d·wk-1 that the participants in this study exercised. Therefore, direct comparison of the results is not possible.
There is considerable anecdotal evidence and a limited amount of experimental research suggesting that brief periods of exercise deprivation in habitual exercisers is associated with mood disturbances. On the basis of this investigation, it is concluded that habitual exercises can experience mood disturbances within 48-h of exercise deprivation.
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Keywords:©1996The American College of Sports Medicine
ANXIETY; DEPRESSION; PHYSICAL ACTIVITY; DEPENDENCE; ADDICTION