A large body of experimental evidence indicates that nonanxious individuals exhibit small (∼ 0.25 standard deviation) but consistent reductions in state anxiety scores following a single bout of exercise (28). However, little is known about the psychological consequences of acute exercise for those with anxiety problems.
To the best of our knowledge, there are no published studies documenting the influence of acute exercise on state anxiety in individuals with clinically diagnosed anxiety disorders. In the 1960s, it was hypothesized by Pitts and McClure (29) that exercise-induced elevations in lactic acid would produce anxiety attacks in panic-prone individuals. This hypothesis has been repeatedly rejected by work showing that intense exercise does not cause panic attacks in those who suffer from panic disorder (7,19,22,24,38,41). Nevertheless, and perhaps because of the Pitts-McClure hypothesis, it has been reported that primary care physicians less frequently prescribe exercise for patients with anxiety than other physical and mental health problems such as obesity and depressive disorders (2).
A few studies have examined the influence of acute exercise on individuals with nonclinical anxiety concerns; however, these have either failed to make a convincing case that the group labeled as high anxious actually possessed high anxiety scores (3), failed to report raw data (42), failed to adequately operationalize anxiety (8), or were otherwise methodologically flawed (27,35). For example, deVries and Adams (8) reported that resting biceps muscle electrical activity was reduced following walking exercise in elderly individuals with self-reported anxiety problems. Although this is of relevance to the anxiety consequences of exercise, the covariation between feelings of anxiety, and biceps EMG, a putative physiological indicator of anxiety is unclear. Thus, the small corpus of relevant literature reveals that relatively little is known about the influence of an acute bout of exercise on anxiety in highly anxious persons.
A number of mechanisms have been proposed to explain why state anxiety is reduced following an acute bout of exercise. One hypothesis suggests that exercise-induced increases in brain opioids result in a heightened positive mood (23). A second hypothesis contends that exercise-induced increases in hypothalamic temperature promote tension reduction following exercise (18,28,43). A third hypothesis is that anxiety reductions following exercise may be caused by a postexercise decrease in anterior right, as compared to left, brain cortical activity measured via electroencephalography (16). Research concerning these hypotheses has yielded equivocal results.
A fourth hypothesis posits that time away or a "time out" from one's cares and worries is responsible for the anxiolytic effects of acute exercise (3). This hypothesis was developed from work showing that acute exercise, meditation, and quiet rest all had similar anxiolytic effects. It was argued that the common element among these procedures is that time is taken out from one's daily routine, thereby resulting in a break from whatever is causing an individual problems or worry (3). The design of the original study was not intended to test the "time out" hypothesis but to compare vigorous exercise to the "relaxation response" in the usefulness of these procedures to reduce state anxiety. Bahrke and Morgan (3) reported that the anxiety reduction following the control condition and their eventual development of the "time out" hypothesis was "a truly serendipitous finding." To the best of our knowledge, there have been no experimental tests of this hypothesis.
The primary purpose of this study was to test the "time out" hypothesis with high trait anxious individuals. It was hypothesized that high trait anxious participants who completed an acute bout of vigorous exercise would report reductions in state anxiety, whereas high trait anxious individuals who performed the same exercise, but were prevented from taking a time out, would not report reductions in anxiety. Because academics are a major stressor in the lives of college students, it was reasoned that if students were studying during exercise, time out would be prevented.
A second purpose was to document the magnitude of the change in state anxiety after an acute bout of exercise in high trait anxious females. It was hypothesized that these individuals would exhibit moderate-to-large reductions in state anxiety following an acute bout of exercise.
METHODS
Subject Recruitment
Solely females were recruited as anxiety problems have been shown to be more prevalent in the female population (33). Participants completed the study in partial fulfillment of a requirement for their psychology classes. Female students (N = 471) in undergraduate psychology classes (N = 16) completed several questionnaires to determine eligibility. One criterion was elevated trait anxiety scores. We sought a sample with a mean trait anxiety score at least one standard deviation above the female college student norms (mean = 40.40, SD = 10.15) (36).
All potential participants completed a self-administered Medical History Questionnaire and the Physical Activity Readiness Questionnaire (1). Those who reported smoking (N = 0), use of medications (N = 0), or the presence of any disease contraindicated for the completion of maximal exercise (e.g., cardiac complications) (N = 0) were excluded from participation in the study.
We sought a group that engaged in a moderate amount of physical activity. Physical activity was measured by the 7-d recall of physical activity questionnaire (4). The rationale for this assessment was to avoid including individuals for whom exercise would be a novel experience (i.e., operationalized here as scores below 25 kcal·kg−1·d−1).
Potential participants were asked to report "the number of hours you spend studying during an average 7-day period." Those who reported studying 14 h or more per week were eligible based on a pilot study of 30 female students enrolled in a psychology course at a large southeastern university who reported a mean (±SD) of 12.75 ± 2 h·wk−1 of study time. This criterion was used to ensure that each participant spent more than an average amount of time studying, and thereby constituting a significant portion of the normal daily routine. Participants also were asked to identify the three greatest "stressors in their lives." Eighty-nine percent of the participants identified school or academics as their top "stressor."
Thirty-six of the 471 possible participants were eligible to participate. Twenty-two initially agreed to participate, and complete data were obtained from 18 participants. The requirements of the study were explained by the experimenter, and participants then signed an informed consent agreement, approved by the Institutional Review Board for Human Subjects. All participants were treated in accordance with the published MSSE policy statement regarding the use of human subjects and written informed consent.
Procedures
V˙O2peaktesting. Each participant performed a maximal exercise test for the determination of peak oxygen uptake (V˙O2peak) using procedures similar to those of Storer et al. (39). The cycle ergometer protocol began with participants cycling for 5 min at 25 W for a warm up. Once the warm up was completed, the cycle ergometer work rate was continually increased in 24 W·min−1 increments until the participant reached her voluntary tolerance. Pedal rate was maintained at 50-70 rpm throughout the test and was verified by a built-in pedal revolution counter. Participants were verbally encouraged to give a maximal effort. The purpose of the V˙O2peak test was to ensure that each participant completed subsequent submaximal exercise bouts at an equal exercise intensity relative to their maximum.
Exercise-only condition. This condition involved 20 min of stationary cycling at a resistance designed to elicit 40% of V˙O2peak. The primary reason for selecting low intensity exercise of 40% V˙O2peak was to ensure that the participants would be able to study while exercising in the Exercise/Study condition. Prior research has shown a relationship between exercise intensity and attentional foci (34). As exercise intensity increases, the exerciser pays increasingly greater attention to bodily functions (e.g., leg pain, breathing, etc.) to perform the task. In addition, this low exercise intensity served to minimize physiological changes that have been hypothesized to account for anxiety reductions following exercise (e.g., elevations in core body temperature or endogenous opioids). Oxygen consumption was monitored twice during exercise to document exercise intensity. A 20-min recovery period where the participant remained seated on the bike followed exercise. Immediately before and 20 min after exercise, participants completed a state anxiety questionnaire. Timing of the postexercise state anxiety assessment was selected based on research showing the greatest reductions in state anxiety following exercise occur at 20 min postexercise (28). The timing of the anxiety measurements was the same in each condition.
Exercise/study condition. This condition was identical to the exercise condition with one exception. The participants read a chapter from the psychology text required by their current psychology course throughout the 40-min test session. The Exercise/Study condition acted as a test of the "time out" hypothesis. That is, by studying during exercise, students were prevented from taking time away from one of their top stressors. This paradigm is distinct from prior research in which subjects have performed cognitive tasks of no personal relevance during exercise (14).
Study condition. This condition was identical to the Exercise/Study condition except that no exercise was performed, thus the participants studied on the cycle ergometer for 40 min. Participants were given an unannounced quiz at the end of both the Exercise/Study and Study conditions to determine if attention was paid to the material. The purpose of this condition was to assess whether anxiety reduction occurred owing to some component inherent in studying per se.
Control condition. This condition involved the participants sitting quietly on the bicycle ergometer for 40 min. The participants were told to remain seated on the bike, not to pedal, and report their cognitions (see report of cognitions below). The purpose of this condition was to assess whether anxiety reduction occurred simply because of the passage of time while in the experimental milieu.
Participants acted as their own controls and participated in all conditions on separate days. Participants completed the precondition anxiety assessment and then were informed as to which condition they would complete that day. The temperature and relative humidity of the testing environment was kept within a narrow range (22 ± 2°C and 40-50% RH, respectively). Participants reported abstaining from exercise, eating, drinking alcohol or caffeinated beverages, and using tobacco products for at least 2 h before testing. The time of day at which testing was conducted was standardized within, but not between, subjects.
Report of cognitions. The purpose of this manipulation check was to document whether the participants were prevented from taking "time out" from their typical cares and worries during the Exercise/Study condition. This procedure also acted as a check of the participants' attention to the materials they were reading as well as a check to see if the participants were taking a "time out" from their academic stressors or if they were ruminating about such scholastic concerns during the Exercise Only condition. The participants were taught how to verbally report their cognitions in response to a soft, brief tone that sounded every 5 min during the experimental conditions (11). Specifically, they answered two questions regarding their current thoughts while exercising: 1) what were you thinking about just before the tone sounded? and 2) can you describe your thoughts in more detail? (e.g., indicate who, what, when, or where if it is appropriate). Reporting of cognitions occurred in every condition.
Materials
Exercise testing. Exercise was performed on an electrically braked, computer-driven cycle ergometer (Minjhardt, model KEM-3). Oxygen consumption was determined using a Sensormedics Metabolic Cart (model 2900). Gas analyzers were calibrated before each test using gas standards verified by the micro-Schollander method. The gas meter and analyzers were interfaced with an IBM-PC microcomputer that calculates 20-s averages for each of the metabolic measures. Heart rate was monitored using Uniq Heart watches (model 8799). Ratings of perceived exertion (RPE) were obtained each minute (5) following standardized procedures (1).
Anxiety assessments. State and trait anxiety were measured by the state (Y-1) and trait (Y-2) portion of the State-Trait Anxiety Inventory (STAI; Y form) (36). There is substantial evidence to support the construct validity of both the state and trait anxiety scales (36,37).
The materials studied by the participants were chapters taken from the psychology text book they were using in class. The chapters were previously screened by the experimenter so that there was no material presented that had information regarding anxiety, exercise, or research design.
Data Analysis
Data reduction. Tape-recorded cognitions were transcribed and coded so that the conditions were made blind to raters. Cognitions were rated separately by two individuals as either academically related or not academically related. Inter-rater reliability was found to be high (r = 0.98). Data regarding cognitions were examined, and it was revealed that one participant in the Exercise/Study condition and three participants in the Study. Only condition reported thoughts about the material that they were supposed to be studying less than 50% of the time they were queried. Because this failure to comply with the experimental instructions compromised one of the main hypotheses, these four subjects were deleted from the subsequent analyses.
Preliminary analyses. The relative exercise intensity did not differ between the two exercise conditions, and both the Exercise Only (41.2% ± 2.6% V˙O2peak) and the Exercise/Study (39.5% ± 1.0% V˙O2peak) conditions approximated the desired intensity of 40%.
Quiz results from both the Study Only (on average 90% ± 3% correct) and the Exercise/Study (on average 92% ± 3% correct) conditions indicated that the participants attended to the reading material.
Selected subject characteristics as well as the results of the maximal exercise test and 7-d physical activity recall are presented in Table 1.
;)
TABLE 1: N = 14).
State anxiety results, including the effect size (d), are presented in Table 2(6). As expected, there was no significant pre-to-post change in state anxiety for either the Study Only (t = 0.7, df = 13, P = 0.50, d = 0.24) or the Control condition (t = −0.5, df = 13, P = 0.65, d = −0.09). As expected, state anxiety was reduced significantly following the Exercise Only condition (mean raw change score ± 95% confidence interval (CI) of 4.3 ± 3.5, t = 2.3, df = 13, P = 0.04). The 95% CI did not include zero after adjusting for precondition anxiety scores (adjusted change score ± 95% CI of 3.3 ± 3.2). ANCOVA was used to generate state anxiety change scores adjusted for the precondition state anxiety values.
TABLE 2: State anxiety scores in the four conditions and the corresponding effect sizes.
Primary analysis. Two questions of primary interest were identified a priori: 1) are anxiety reductions following exercise blocked when individuals are prevented from taking time out while exercising? and 2) what is the magnitude of the state anxiety reduction following exercise compared to control? The first question was addressed by a planned comparison of the Exercise/Study conditions using a dependent t-test on both raw and adjusted pre-to-post change scores. The second question was addressed by computing the effect size (d) (6). ANOVA was not utilized in the primary analysis because the overall F-test results would not yield meaningful information specific to the hypotheses.
PRIMARY RESULTS
State anxiety was not reduced following exercise in the Exercise/Study condition (t = −0.05, P = 0.97, df = 13, d = 0.01), and the associated CIs included zero (unadjusted 0.1 ± 3.4, adjusted 0.8 ± 3.2). The magnitude of change in state anxiety following Exercise Only represented an effect size of d = 0.52.
DISCUSSION
Test of the time out hypothesis. It was hypothesized that high trait anxious participants who were prevented from taking a "time out," by studying while exercising, would not report a reduction in anxiety following exercise. The results indicated that the anxiolytic effects of exercise were essentially blocked by studying while exercising. Therefore, the findings support the hypothesis that anxious females feel better following low intensity (i.e., aerobic) exercise because it provides them a "time out" from daily cares and worries.
The results from this study extend those of Bahrke and Morgan (3) by providing stronger experimental support for the "time out" hypothesis. The fact that state anxiety was not reduced after the participants sat quietly on the cycle ergometer indicated that the passage of time did not cause the reduction in state anxiety in the Exercise Only condition. Several studies have found state anxiety reductions following quiet rest (3,31). In these studies, participants sat quietly, resting in a comfortable chair while sitting in a sound attenuated chamber. In the present investigation, the participants sat on an uncomfortable bicycle seat in a sterile, windowless room which may have negated potential anxiety reductions previously observed following quiet rest conditions.
The Study Only condition served as an attentional control group. It is theoretically possible that experimental participants who are given any treatment will exhibit anxiety reductions. The nonsignificant change in state anxiety following the Study Only condition argues against the notion that the anxiety reduction following the Exercise Only condition was because of the attention that participation afforded the participant.
One limitation of the present study was that the mean pre-exercise state anxiety scores were not identical across the four conditions. Thus, it is possible that the failure to observe a significant anxiety reduction in the Exercise/Study condition was, in part, because of the somewhat lower preexercise state anxiety value in this condition. It is important to recognize, however, that large decreases in state anxiety were in no way prevented by a floor effect in the Exercise/Study condition. Indeed, most studies documenting anxiety reductions following exercise have reported a mean preexercise state anxiety value approximately 1 SD below the value reported here in the Exercise/Study condition (25,31).
Although the present findings can be interpreted as supportive of the time out hypothesis, it is not possible to rule out all other plausible alternative explanations. For example, hypothalamic temperature or central nervous system opioid concentrations were not measured in the present study and, therefore, cannot be dismissed in a compelling fashion as possible contributors to the results. However, we are unaware of any strong reason to believe that these factors would vary systematically across the exercise conditions employed in the present experimental paradigm.
Magnitude of anxiety reduction. A second primary finding of this experiment was that 20 min of low intensity (40% V˙O2peak) cycling by high trait anxious college women resulted in a reduction in state anxiety. The magnitude of the state anxiety reduction (d = 0.52) was greater than what has been reported to occur in nonanxious normal individuals (d = 0.24) (28). Several factors may have influenced the magnitude of the anxiety reduction observed, including the intensity and duration of the exercise, the initial state anxiety values, and the fitness level of the participants.
The ideal exercise stimulus for maximal anxiety reduction is unknown. A quantitative synthesis of the literature reported that the largest anxiety reductions occur following exercise of either 21-30 min in duration or at an intensity of >80% of HRpeak or V˙O2peak(28). One major limitation of that review, however, is that it was based almost entirely on correlational data. Experiments in which investigators directly manipulated the exercise intensity to examine the subsequent anxiety response have yielded mixed results with low intensity exercise (13,32,40). Significant anxiety reductions in nonanxious individuals following 20 min of stationary leg cycling at an exercise intensity as low as 40% V˙O2peak have been reported (22), but in another study reductions in state anxiety following 80 min of running at 40% V˙O2peak were not observed (13). The mixed results may be due in part to the fact that the samples tested possessed low preexercise anxiety scores. The present investigation shows that low intensity exercise is anxiolytic for college women with elevated trait anxiety scores.
In the present investigation, the mean preexercise state anxiety scores across the four conditions was 40.7. This value is 1) approximately one-third of a standard deviation above the mean for normal nonanxious college females (38 ± 10) (36) and 2) approximately one standard deviation above the mean preexercise state anxiety values typically reported in the related literature (∼31) (25). It is plausible that in prior studies the preexercise values have been lower than published norms because high anxious individuals have elected to not participate in studies involving exercise. The initial values in the present investigation were clearly high enough to allow for anxiety reduction following exercise. That is, there was no "floor effect" as frequently has been the case in studies of nonanxious normal individuals. Nevertheless, had the preexercise state anxiety values been higher, as might be expected based on the sample's mean trait anxiety score of 50.9, it is plausible that a larger postexercise reduction in anxiety would have occurred.
Martinsen et al. (19) reported that "patients with anxiety and depressive disorders are less fit than the general population." Our data agree with Martinsen et al. in that the participants in this study had below average V˙O2peak values (34.2 mL·kg−1·min−1 vs 42 for college women) (21), and average self-reported activity levels (37.3 kcal·kg−1·day−1 vs 35-38 for normal individuals) (10). There have been only a few studies examining the possible role of fitness on anxiety reduction following exercise. This work has failed to produce consistent or compelling evidence that fitness influences the anxiolytic effect of exercise (9,25,35). The present findings revealed that low-fit anxious females reported a reduction in anxiety following low intensity exercise.
Potential clinical relevance. Anxiety is commonly treated with relaxation techniques and antianxiety medications (20,30). The results of the present investigation demonstrate that the magnitude of the anxiety reduction following acute exercise is similar to that which accrues in association with relaxation (12) and mediation (17) procedures. This observation is consistent with prior reports showing a similarity between anxiety reductions following aerobic exercise and those following a period of quiet rest (3,15,31). In addition, one study found that exercise reduced elbow flexor EMG activity ∼15% more than 400 mg of meprobamate in an elderly sample with self-reported anxiety difficulties (8). Thus, exercise compared favorably with an older-generation antianxiety medication. We are unaware of any comparable work with clinical samples or newer antianxiety medications. Exercise, therefore, seems to be as effective as several relaxation and meditation techniques and is more effective than one antianxiety medication. This being true, should anxious individuals exercise if they can achieve similar mental health effects while sitting quietly or performing some passive form of relaxation?
Raglin and Morgan (31) reported that state anxiety and systolic blood pressure were reduced following both exercise and quiet rest in a sample of nonanxious males. These variables remained reduced for 2-3 h postexercise, but more quickly (20 min postcondition) returned to baseline levels following quiet rest. Thus, the effects of an acute bout of exercise have been shown to be more long-lasting than physically passive alternatives. Moreover, adaptations associated with chronic exercise such as reduced blood pressure, weight maintenance and loss, and an improved serum cholesterol profile mean that exercise can make a demonstrable contribution to improved physical health (26).
CONCLUSION
Based on the findings of the present experiment, it is concluded that high trait anxious college females exhibit significant state anxiety reductions following low intensity (40% V˙O2peak) cycling of 20 min duration. In addition, the findings support the idea that "time out" is a plausible mechanism by which the anxiolytic effects of exercise are realized.
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