Mood alteration after 15 minutes of preferred intensity exercise: examining heart rate, perceived exertion, and enjoyment.

Berger, Bonnie G. ; Darby, Lynn A. ; Zhang, Yu 等

Acute mood changes after a single exercise session have been documented in a variety of populations (e.g., Berger, Darby, Owen, & Carels, 2010; Cox, Thomas, Hinton, & Donahue, 2004; Petruzzello, Snook, Gliottoni, & Motl, 2009; Rokka, Mavridis, & Kouli, 2010). However, mood changes are not always automatic or in desirable directions (Berger & Tobar, 2011; Ekkekakis, Parfitt, & Petruzzello, 2011). Exercise intensity has been suggested as one factor that may influence the direction and extent of the mood changes. For example, both moderate and sometimes low intensity exercise have been associated with desirable mood changes (Berger & Owen, 1998; Lind, Ekkekakis, & Vazou, 2008; Stych & Parfitt, 2011). However, when exercising at a high exercise intensity, mood improvements have been elusive with some researchers reporting no mood changes and others reporting mood decrements as well as benefits (Berger & Motl, 2000; Berger & Owen, 1992; Cox et al., 2004; Hall, Ekkekakis, & Petruzzello, 2002; Rose & Parfitt, 2007; Tobar, 2012). As concluded by Ekkekakis (2009), the multiple ways of measuring and establishing exercise intensity can confound drawing conclusions as to the "best" exercise intensity for reaping mood benefits.

Further confounding the exercise-mood relationship, exercise duration in addition to intensity may influence the extent of mood changes (Berger & Tobar, 2011; Carels, Coit, Young, & Berger, 2007). Based on the health-related American College of Sports Medicine (ACSM) guidelines (2014) for including 10-minute exercise sessions throughout the day to accumulate the needed 30 minutes of moderate intensity exercise, it is important to investigate exercise sessions of short duration to better understand the potential psychological benefits. Typically researchers have investigated the mood benefits in exercise sessions of 20-40 minutes when investigating mood alteration (e.g., Glass & Chvala, 2001; Lind et al., 2008; Raedeke, 2007). Few researchers have reported mood benefits after 10, 15, or 20-minute sessions (Annesi, 2003; Rudolph & Butki, 1998). Thus, relatively little is known about the psychological benefits of short-duration exercise sessions. This study focused on the mood benefits of brief 15-minute exercise sessions performed at a preferred intensity.

Preferred exercise intensity and self-selected exercise intensity are somewhat similar concepts. Both can include low, moderate, and high intensity levels of exercise because the intensity is determined by the participants themselves. However, preferred exercise intensity is based on participants' experiences of enjoyment and pleasure at that particular intensity and one that they would be happy to do regularly (Parfitt, Rose, & Markland, 2000). As emphasized by Parfitt and colleagues, preferred intensity exercise includes an element of choice. For example, some individuals may enjoy light intensity exercise (20-39% HRR; ACSM, 2014). Light intensity exercise tends to be invigorating rather than tiring, and can provide an enjoyable "time out" from the stressors of the day. Other individuals may prefer moderate intensity exercise (40-59% HRR). Moderate intensity exercise results in desirable physiological changes such as weight loss and aerobic fitness, and can be accompanied by relatively pleasant physical sensations. Still other individuals may prefer high intensity exercise (60-77% HRR). They can reap the physiological benefits of exercise in the shortest amount of time possible, are challenging themselves physically and may enjoy the stimulation of physical sensations resulting from high intensity exercise.

In contrast to preferred intensity exercise, self-selected intensity reflects the participant's pragmatic consideration of exercise goals such as weight loss, muscle definition, aerobic fitness, and personal challenge. For example, someone who prefers and enjoys exercising at a moderate intensity could self-select a high exercise intensity session to reach the goal of expending as many calories as possible in the exercise session. When examining mood alteration after exercising at either preferred or self-selected exercise intensity levels, researchers have concluded that participants had desirable mood changes (DaSilva et al., 2011; Ekkekakis & Lind, 2006; Lind, et al., 2008; Parfitt, Rose, & Burgess, 2006). However, exercising at a slightly increased exercise intensity that is beyond the self-selected exercise intensity and above the ventilatory threshold may lead to a decrease in pleasure (Ekkekakis & Lind, 2006; Lind et al., 2008). Because individuals may prefer a variety of intensities, it is important to delineate the preferred exercise intensities that may affect mood change and have implications for health benefits.

Many participants tend to exercise at a moderate intensity within the range of 40% to 60% heart rate reserve (HRR) that is recommended for health and fitness by American College of Sports Medicine (ACSM, 2014) and as suggested for mood change by Berger and colleagues (Berger, Pargman, & Weinberg., 2007). However, some participants have chosen a lower or higher intensity levels than this recommended range (Ekkekakis, 2009). Thus, this study examined the exercise intensity ranges as determined by heart rate reserve (HRR) and rate of perceived exertion (RPE) that college students prefer.

Because not all exercisers experience the same mood benefits (Raedeke, 2007), it has been hypothesized that exercise enjoyment characterized by pleasure, liking, and fun may play a key role in maximizing the mood benefits of exercising (Berger, 1996; Berger et al., 2007; Wankel, 1993). Ekkekakis et al. (2011) recommended a tripartite model for exercise prescriptions: maximization of effectiveness, minimization of injury, and consideration of pleasure. Enjoyment can lead to mood elevation, and mood elevation can lead to perceptions of enjoyment. For example, participating in any enjoyable activity such as exercise may be mood elevating; however, the causal relationship could be reversed. Parfitt and colleagues (2000) stated that mood elevation and feelings of well-being after exercising may influence exercise enjoyment and subsequent participation. In other words, experiencing mood elevation after exercising could lead to the conclusion that exercise is enjoyable.

The relationship between mood change and exercise enjoyment, however, has not been fully delineated. One study with male rock-climbers and students in a health education class indicated that exercise enjoyment as measured by the Physical Activity Enjoyment Scale (PACES; Kendzierski & DiCarlo, 1991) was related (r = .46) to mood change scores (Motl, Berger, & Leuschen, 2000). Rock climbers who had higher enjoyment scores reported greater mood benefits. Another study with college students revealed that exercise enjoyment as measured by the PACES was related to increases in vigor (r = .39), but not to decreases in negative mood states on the POMS subscales (Raedeke, 2007). Still another study with obese adults who walked on a treadmill found no evidence of a relationship between exercise enjoyment and acute changes in mood (Berger, et al, 2010). At the present time, it is not clear that the exercise experience needs to be enjoyable in order for participants to report desirable changes in mood states.

The present study investigated the parameters of preferred exercise intensity in college students and the proposed role of exercise enjoyment in Berger's (1996, 2004, 2009; Berger et al., 2007; Berger & Tobar, 2007) taxonomy which also includes other major exercise factors of mode and training factors of intensity, duration, and frequency. The taxonomy highlights these exercise factors as key influences on mood elevation and other psychological benefits. In this study, we investigated preferred exercise intensity levels selected by college students, their mood changes when exercising for 15 minutes at their preferred intensity levels, and also the relationship between mood change and exercise enjoyment. Hypotheses in the present study were as follows. The first hypothesis (HI) was that college students will select a moderate intensity level as their preferred exercise intensity, because it is pleasant and is not so physically taxing that it results in breathlessness or fatigue. It also was hypothesized (H2) that participants will report desirable mood changes after a brief, 15-minute session of jogging at a preferred intensity. The final hypothesis (H3) was that exercisers who report higher scores on exercise enjoyment will report greater mood improvements than those with lower enjoyment scores.

Method

Participants

College students (N = 55; 28 men, 27 women) from a midwestem university completed this study. Because the heart rate monitors of two participants failed to record scores, analyses that included heart rate were based on 53 students. The mean age was 20.6 (SD = 1.4) years and mean body mass index (BMI) was 23.8 (SD = 4.0) kg/[m.sup.2]. As reflected by their self-reported mean exercise time of 288 minutes (4.8 hrs.) per week, participants were physically active. Demographic data for males and females are provided in Table 1. There were no significant differences between males and females except for the anticipated differences in height, body weight, and BMI.

Measures

Percent of heart rate reserve (percent HRR). Heart rate monitors (Polar Model S120[TM]) were employed to measure participants' heart rates during the exercise. This objective measure of exercise intensity was represented by percent HRR and five categories as defined by the ACSM (2014).

Scores for percent HRR were calculated using the following formula: percent HRR = % (HRexercise--HRrest) / (HRmax--HRrest) where age-predicted HRmax = 206.9--(0.67 [] age) (ACSM, 2014). Intensity categories for percent HHR were as follows: very light (< 20% HRR), light (20-39% HRR), moderate (40-59% HRR), hard (60-84% HRR), and very hard ([greater than or equal to] 85% HRR).

Perceived exertion. The Rating of Perceived Exertion (RPE) Scale was employed to measure exercise intensity (Borg, 1998). Participants indicated how hard they were working during exercise, and scores ranged from 6 to 20. Exercisers' verbal indicators ranged from "no exertion at all" (rating of 6), to "somewhat hard" (rating of 13), to" maximal exertion" (rating of 20) for each lap that they completed (ACSM, 2014). When rating perceived exertion, participants were asked to concentrate on a gestalt composed of multiple factors such as somatic symptoms, sensory cues, and emotional factors as reported by Borg (1998). RPE is a subjective rating of exercise intensity and is strongly correlated with heart rate (Jakicic, Donnelly, Pronk, Jawad, & Jacobsen, 1995; Scherr et al., 2013).

Mood states. The Profile of Mood States (POMS) was employed as a state measure of mood and included six subscales: Tension, Depression, Anger, Vigor, Fatigue, and Confusion (McNair, Lorr, & Droppleman, 1992). Participants rated the 65 items on the POMS to describe their mood states. Responses to each item ranged from 0 (not at all) to 4 (extremely). Instructions asked participants, "How do you feel right now?" The internal consistency reliability coefficients for the POMS have ranged from 0.84 to 0.95, and test-retest reliability coefficients have been reported to range from 0.65 to 0.74 (McNair et ah, 1992). In the present study, Cronbach's alpha coefficients of internal consistency were calculated for each of the six subscales for students' (N= 55) pre-exercise responses. Internal consistency was very good to excellent for the following subscales: Tension, [varies] = 0 .86, (9 items); Depression, [varies] = 0 .93 (15 items); Anger, [varies] = 0.88 (12 items); Vigor, [varies] = 0.83 (8 items); Fatigue, [varies] = 0.89 (7 items). Internal consistency for Confusion, [varies] = 0.58 (7 items), was fair to poor, and findings should be interpreted with caution for this subscale.

Exercise Enjoyment. The original version of Physical Activity Enjoyment Scale (PACES) developed to measure physical activity enjoyment in college students was employed in the present study to measure exercise enjoyment (Kendzierski & DeCarlo, 1991). The Scale includes 18 items that are rated on a seven-point bipolar scale (e.g., 1 enjoy it; I feel bored). Instructions for the trait version of the PACES were as follows: "Please rate how you feel about most types of physical activity in general, most of the time." After reversing the negative scores, item scores then were summed to provide a unidimensional measure of enjoyment. A subsequent evaluation of the validity of the PACES in a sample of 1,797 eighth-grade girls indicted support for enjoyment as a single factor with irrelevant methodological effects for positively and negatively worded items (Motl, et al., 2001). Similar results for positive and negatively-worded items along with gender and age differences in enjoyment have been reported for an Italian version of the PACES when testing 5,934 Italian students aged 11 to 19 years (Carraro, Young, & Robazza, 2008). Internal consistency reliability of the PACES has been reported to be 0.96, and test-retest reliability coefficients have ranged from 0.60 to 0.93 (Kendzierski & DeCarlo, 1991). In the present study, Cronbach's alpha coefficient of internal consistency for trait enjoyment of exercise was excellent, [varies] = 0.92 (18 items; N = 55).

Procedure

After obtaining study approval from the university's Human Subjects Review Board, students in three jogging classes (with approximately the same proportion of men and women in each class) met two days a week in 50-minute sessions and were invited to participate. Orientation did not begin until week 7 of a 15-week semester in order that students were able to develop a fitness base for continuous jogging during the first seven weeks of the course. Establishing a fitness base was an important procedure, because regular exercisers and non-exercisers have differed in the acute mood benefits of exercise, especially for Vigor and Fatigue as reported by Hoffman & Hoffman (2008).

In the first orientation session, students who agreed to participate signed an informed consent form. They then completed a demographic questionnaire that included questions about gender, age, height, weight, and habitual exercise time per week. Students also completed the trait version of the PACES as a measure of how much they enjoyed exercise in general across exercise modes, intensities, duration, and situations.

In a second orientation session, participants became familiar with using the heart rate monitors, the verbal anchors for RPE ratings, and general study procedures. Participants also practiced using heart rate monitors while they jogged at a preferred intensity--a level that they enjoyed and could sustain for a 15-minute session (Parfitt et al., 2000). Fifteen minutes was selected to represent the maximal amount of time that moderately fit students could jog for a continuous amount of time. In addition, most students can find the necessary time to exercise for a 15-minute period in their highly scheduled days. Thus, 15 minutes was the exercise duration selected for several pragmatic reasons. While jogging or running (ACSM, 2014) during this second orientation session, participants gained experience reporting their RPE as they passed trained research assistants on each lap of a 1/8-mile indoor track.

On the testing day held in the 8th week of the semester, the researcher and participants reviewed the RPE scoring system in an effort to enhance students' accuracy in its use. Participants subsequently completed the state version of the POMS by indicating how they felt at that moment immediately before exercising. They were instructed to exercise by themselves and at their preferred pace to reduce the social effects of exercising in a group setting. All participants started and finished exercising at the same time. The researcher and assistants recorded each participant's heart rate for each lap when exercisers reported their RPE as they passed designated locations on the track. To determine RPE scores, each exerciser responded to the question, "How hard are you working?" (Borg, 1998). This procedure was followed for each lap completed. After 15 minutes of jogging, participants cooled down by walking for approximately 20 yards for two minutes to a classroom immediately adjacent to the track where they completed the post-exercise POMS.

Analysis

Statistical analyses were completed using SPSS Version 20.0. Mean scores for Heart Rate, RPE, and percent HRR responses were computed for each participant for the 15-minute exercise period. Chi-square tests were performed to evaluate whether the observed exercise intensities as reflected by percent HRR and RPE preferred by men and women differed from the expected frequency (i.e., no gender difference for preferred intensity). A Class x Gender x Time (3 x 2 x 2) MANOVA with repeated measures for Time was conducted to assess differences on the six POMS subscales. Another Class x Exercise Enjoyment x Time (3 x 2 x 2) MANOVA with repeated-measures on Time and also a correlation analysis were completed to measure the relationship between exercise enjoyment and mood change. Effect size was reported as partial eta-squared ([[eta].sub.p.sup.2]) as recommended by Tabachnick and Fidell (2012). Observed power was reported from the SPSS analyses.

Results

Class Equivalence Prior to the Exercise Treatment

Prior to addressing major hypotheses of the study, we examined the possibility that participants in the three classes differed on some variables prior to the experimental manipulation. Results of one-way ANOVAs for Class indicated that classes differed significantly on exercise enjoyment [F(2, 52) = 3.416, p = .040]. Classes did not differ on any pre-exercise subscale of the POMS, except for Anger [F(2, 52) = 5.417, p = .007]. The three classes also did not differ significantly for age, height, body weight, BMI, habitual exercise time per week, percent HRR, or RPE. In conclusion, classes did not seem to differ systematically on the dependent variables as measured prior to the exercise treatment.

Preferred Exercise Intensity in College Students: Percent HRR and RPE

Exercise intensity categories suggested by ACSM (2014) of very light, light, moderate, hard, and very hard were employed to classify the males and females (see Table 2). When participants exercised at their preferred exercise intensities, their mean percent HRR was 78.1% (SD [+ or -] 10.3), and RPE was 12.4 (SD [+ or -] 1.5). As reflected in Table 2 for percent HRR, most participants (92.5%) preferred "hard" or "very hard" exercise intensity, and none exercised at the "very light" and "light" intensities. In contrast when analyzing RPE scores, most participants (83%) perceived their exercise intensity as "light" or "moderate." Thus, HI was partially supported; although the participants' objective 78.1% percent HRR indicated a "hard" intensity (ACSM, 2014), their subjective RPE mean score of 12.4 was between the scores of 11 (light) and 13 (somewhat hard) as defined by Borg (1998).

Percent HRR. To examine the possibility of a gender difference for preferred intensity as measured by percent HRR, a Chi-square test of independence was employed [2 (Gender) x 5 (Exercise Intensity)]. Because no students preferred the intensity categories of "very light" and "light," the Chi-square analysis became a 2 (Gender) x 3 (Exercise Intensity). Results indicated that there was no Gender x Exercise Intensity interaction. Therefore, a Chi-square goodness of fit analysis combined male and female students against the expectation of an equal frequency in each intensity. Students showed a distinct preference for specific percent HRR intensities [[chi square](4, N= 53) = 75.396, p < .0005]. Contrary to HI, most participants (92.5%) preferred excising at "hard" or "very hard" exercise intensities, rather than moderate intensity.

RPE. The five intensity categories for RPE were defined by Borg (1998) and refined by Berger and colleagues (2007). Again, a possible gender difference for preferred intensity as measured by RPE was examined in a Chi-square test of independence [2 (Gender) x 5 (Exercise intensity)]. No students reported exercising at the intensity category of "very hard," and the analysis became a 2 (Gender) x 4 (Exercise Intensity). Again, results indicated that the interaction between Gender and Exercise Intensity level was not significant. Therefore the follow-up Chi-square goodness of fit analysis combined male and female students against the expectation that each intensity was equally preferred. Once again, results indicated a significant difference in the preferred exercise intensity [[chi square](4, N = 53) = 45.019, p < .0005]. As shown in Table 2, most participants (83%) perceived their exercise intensity as "light" or "moderate." Thus, HI was partially supported. Participants' objective percent HRR indicated a "hard" exercise intensity (ACSM, 2014). However, their subjective RPE mean score of 12.4 for exercise intensity was between "light" (11) and "somewhat hard" (13) and reflected a moderate intensity as defined by Borg (1998).

Mood Benefits After Exercise

The potential for acute mood benefits associated with only 15 minutes of preferred intensity exercise was examined in a Class x Gender x Time (3 x 2 x 2) MANOVA with repeated measures on the six POMS subscales. Results indicated an interaction between Class, Gender, and Time (pre- and post-exercise), Wilks's [LAMBDA] = .606, F(12, 88) = 2.090,p = .025, [[eta].sub.p.sup.2] = .222, observed power = .908]. Because the three-way interaction was significant, simple-effect follow-up analyses for each class were conducted in a Gender x Time: Preand Post-exercise (2 x 2) MANOVA with repeated-measures on the vector of the six POMS subscales.

In Classes I and II and for the women in Class III, the simple main effect of Time was significant. Therefore, we interpreted the main effect of Time from the three-way MANOVA [Wilks's [LAMBDA] = .441, F(6, 44) = 9.309, p = .000, [[eta].sub.p.sup.2] = .559, observed power = 1.000]. Examination of pre- to post-exercise changes on each of the POMS subscales in Figure 1 indicated support for H2. Exercisers reported a variety of mood benefits. These included decreases in Depression [F(1, 49) = 8.636, p = .005, [[eta].sub.p.sup.2] = . 150; observed power = .821], Anger [F(l, 49) = 18.722, p = .000, [[eta].sub.p.sup.2] = .276; observed power = .989], and Confusion [F(1, 49) = 42.803,p = .000, [[eta].sub.p.sup.2] = .466; observed power = 1.000], respectively, and increases in Vigor [F(1, 49) = 24.011, p = .000, [[eta].sub.p.sup.2] = .329; observed power = .998],

Relationship of Mood Benefits and Exercise Enjoyment

To explore H3 and a possible relationship between acute mood benefits and exercise enjoyment, a 3 (Class) x 2 (Exercise Enjoyment level: High and Low) x 2 (Time: Pre- and Post-exercise) with repeated-measures MANOVA on the vector of the six POMS subscales was calculated. With the Exercise Enjoyment factor defined by a median split of enjoyment scores (trait measure of enjoyment), exercisers in the "low" enjoyment group had a mean score of 83.54 (SD = 10.19; n = 28), and scores ranged from 65 to 100. Exercisers in the "high" enjoyment group had a mean score of 111.22 (SD = 7.28; n = 27), and scores ranged from 101 to 126. Results indicated that there was no evidence of a three-way interaction or a two-way interaction between Exercise Enjoyment x Time. An additional post-hoc analysis was employed to examine the hypothesized relationship between exercise enjoyment and mood change. Difference scores for mood pre- and post-exercise were calculated. Results of the correlation analysis reported in Table 3 indicated that exercise enjoyment was significantly related to a decrease in Anger (r = .255, p = .030). There was little evidence of a relationship between exercise enjoyment and the other POMS subscales. Thus, there was minimal evidence that students who enjoyed exercise more than others differed in their acute mood changes after 15 minutes of jogging.

[FIGURE 1 OMITTED]

Discussion

Parameters of Preferred Exercise Intensity

A major purpose of this study was to examine the percent HRR and RPE parameters of preferred intensity of exercise in college students. Our findings indicated that preferred exercise intensities selected by most students who jogged for a 15-minute period were relatively "hard" and "very hard," as reflected by a mean of 78.1 percent HRR. These results do not support our hypothesis of a preference for a moderate intensity of exercise. Our results, however, do agree with the preferred exercise intensity parameters reported by Glass and Chvala (2001). In their examination of preferred intensity in college-age participants in three types of exercise (treadmill, cycle ergometer, and stair-stepper) for 20 minutes at a preferred intensity, results indicated that exercise intensities for each type of exercise were 74.8, 80.0, and 80.2% HRR, respectively (Glass & Chvala, 2001). Students' preference for a hard (vigorous) exercise intensity meets the requirement for obtaining the fitness and health benefits in regular exercisers (ACSM, 2014). Therefore, fitness and health benefits can be achieved by college students who jog at their preferred intensities provided that they also meet the duration guidelines for the moderate or vigorous intensity exercise outlined by Garber and colleagues (2011).

Male and female students in this study reported similar exercise intensities as measured by percent HRR and RPE (Means: percent HRR = 75.5 and 80.8, and RPE's = 12.45 and 12.37, respectively) when they jogged at a preferred intensity. This lack of a gender difference in preference for exercise intensity supports those of DaSilva and colleagues (2011) who also reported that male and female participants did not differ in RPE when they walked at self-selected paces. In addition, Glass and Chvala (2001) reported RPEs in three different types of exercise that were comparable to our findings. Exercising at their preferred intensities, college-age participants' mean RPEs were 12.50 (treadmill), 12.57 (cycle ergometer), and 12.79 (stair-stepper), respectively. These RPEs were between 11 or "light" to 13 or "somewhat hard" on the Borg (1998) scale.

Although a large proportion (92.5%) of the participants in this study preferred HRR intensities that were "hard" (62.3%) or "very hard" (30.2%) as defined by ACSM (2014), 83% of them perceived that their RPE intensities were light (47.2%) or moderate (35.8%). A similar discrepancy between percent HRR and RPE was reported by Ekkekakis (2009) who found in his review that self-selected intensity as measured by percent HRR, was "moderate" as determined by ACSM (2014), but that exercisers' RPE was considerably lower and ranged from 9 or "very light" to 11 or "light." Our findings on preferred intensity of exercise support those reported by Ekkekakis (2009) for self-selected exercise and who suggested that when exercising at a self-selected intensity, psychological factors such as autonomy and control may influence a decreased perception of physical exertion. These same psychological factors also might influence RPE during preferred intensity exercise. That is, when allowed to determine their preferred exercise intensities, participants may perceive that they are exercising at a lower intensity than when exercise intensity is imposed. An alternative explanation of the apparent discrepancy between percent HRR and RPE is that RPE scores reflect the perception of many physiological and psychological cues which individuals may weigh differentially in the RPE value (Borg, 1998). Because percent HRR is based on one variable and RPE is based on multiple variables and has high inter-individual variability, it is understandable that there may be some divergence between percent HRR and RPE.

Mood Benefits after 15 Minutes of Exercise

It was impressive that exercisers who selected their own exercise intensity levels reported desirable acute mood changes after only 15 minutes of jogging. Although significant changes were not found for all six of the POMS subscales in each of the three classes, the pre- and post-exercise mood changes were in desirable directions.

As noted in Figure 1, mood benefits in the combined classes were significant for Depression, Anger, Vigor, and Confusion. A possible explanation for the overall lack of significant changes for Tension and Fatigue which were significant only for women in Class III may involve the relatively high intensity of exercise as indicated by percent HRR. All students, regardless of Gender, exercised at 78.1 [+ or -] 10.3 percent HRR when they were able to select their exercise intensities. Exercising at this relatively high intensity level was not conducive to reducing Fatigue or Tension, and perhaps the best that can be hoped for is an absence of an undesirable increase in these mood states (Berger & Motl, 2000; Berger & Owen, 1992; Hall et al., 2002; Rose & Parfitt, 2007; Tobar, 2012). Despite the lack of a significant change on Tension and Fatigue, our overall results support the hypothesis that as little as 15 minutes of jogging at a preferred intensity results in mood enhancement as measured by the Depression, Anger, Vigor, and Confusion subscales of the POMS.

Relationship between Mood and Exercise Enjoyment

There was little support for the hypothesized relationship between exercise enjoyment and mood changes after a single exercise session because the relationship was evident only for Anger. People who enjoyed exercise more had less Anger; however, it seems that desirable mood changes occur after as little as 15 minutes of jogging regardless of a person's trait level of exercise enjoyment. These findings support a study of obese participants in which there was no evidence of a relationship between exercise enjoyment and mood change (Berger et al., 2010). Because other researchers have reported a significant relationship (Motl et al., 2000; Raedeke, 2007), further investigation is needed to clarify whether people who enjoy exercise more than others also report greater mood benefits after exercising.

Limitations

It is important to acknowledge several limitations. First, exercising in a group may have confounded our measures of preferred intensity of exercise as indicated by percent HRR and RPE. Exercisers may prefer to exercise at a higher intensity in a group setting as measured by percent HRR than when they exercise alone reflecting the possible influences of social facilitation and self-presentation. (Note that students in this study were instructed to exercise alone at their personal preferred intensity within the class setting.) In addition, college students may report that they are exercising at a lower rate of perceived exertion than they actually perceive, again as a result of social comparison and self-presentation as they demonstrate a sense of superiority to the group. To examine this possibility, future studies of the parameters of preferred exertion in college students need to measure participants' preferred exercise intensity when exercising alone in a laboratory setting to produce results with high internal validity. A second limitation was that participants may have needed additional instruction and practice to exercise at their preferred intensity, an intensity that they truly enjoyed. In this study with only two days of practice, participants may have self-selected an exercise intensity necessary to reach their fitness goals, rather than one that truly was enjoyable. Future studies of preferred and self-selected exercise intensity need to clearly distinguish which of these two intensity choices participants have followed. Despite these limitations, this study presents new infomiation about the parameters of college students' preferred exercise intensity and mood change when jogging for only 15 minutes in a real-world group environment that is common to many exercise classes.

Conclusions

This study has implications for college students when exercising at a preferred intensity. First, students actually preferred a hard exercise intensity and thus met ACSM (2014) intensity guidelines for achieving fitness and health benefits. Second, when students select their own preferred exercise intensity, they may exercise at a higher intensity (percent HRR) than they perceive as reported by RPE. Finally, it was impressive that college students can experience acute mood benefits after only 15 minutes of jogging at their preferred intensities.

Bonnie G. Berger

Lynn A. Darby

Yu Zhang

Bowling Green State University

David R. Owen

Brooklyn College of the City University of New York

David A. Tobar

Bowling Green State University

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Table 1
Demographic Characteristics of Participants (N = 55)

                                                              All
                          Males            Females       Participants
                         (n = 28)          (n = 27)        (N = 55)

Variable                M       SD        M       SD       M      SD

Age (yrs)             20.7      1.3     20.6      1.5    20.6     1.4
Height (cm)          179.8 *    8.7    165.1 *    5.9    172.6   10.5
Weight (lb)          182.3 *   35.2    132.7 *   15.6    158.0   36.9
BMI (kg/[m.sup.2])   25.5 *     4.5    22.1 *     2.4    23.8     4.0
ExTime(min)/Wk        300.0    235.0    276.0    208.0   288.0   221.0

Note. ExTime/Wk = Self-reported exercise time per week from the
Paffenbarger Physical Activity Questionnaire (Paffenbarger, 1997).
* p [less than or equal to] .05; Males > Females

Table 2
Percentage and Numbers of Participants Who Chose a Preferred Exercise
Intensity Represented by %HRR and RPE Categories (N = 53)

                                     %HRR

Intensity           Level of       % of    Males   Females
Categories            %HRR           N      (n)      (n)     N

Very Light            <20          0.0%      0        0      0
  Light              20-39         0.0%      0        0      0
Moderate/
Somewhat Hard        40-59         7.5%      3        1      4
  Hard               60-84         62.3%    16       17      33
Very Hard       [greater than or   30.2%     8        8      16
                  equal to] 85

                                      RPE

Intensity           Level of       % of    Males   Females
Categories            RPE            N      (n)      (n)     N

Very Light            8-10         13.2%     3        4      7
  Light              11-12         47.2%    12       13      25
Moderate/
Somewhat Hard        13-14         35.8%    11        8      19
  Hard               15-17         3.8%      1        1      2
Very Hard       [greater than or   0.0%      0        0      0
                  equal to] 18

Table 3
Results of Correlations Analyses Between Exercise Enjoyment
and Change Scores on the Six POMS Subscales (N = 55)

Variables    PACES   Tension   Depression   Anger

PACES         --      -.014       .024      .255 *
Tension                --        .493 *     .459 *
Depression                         --       .578 *
Anger                                         --
Vigor
Fatigue
Confusion

Variables     Vigor    Fatigue   Confusion

PACES         -.003     .057       .062
Tension      -.447 *   .569 *     .558 *
Depression    -.200     .256      .626 *
Anger        -.290 *    .217      .589 *
Vigor          --      -.439 *    -.417 *
Fatigue                  --        .196
Confusion                           --

* p < 0.05; change score = Pre-exercise mood score--Post-exercise
mood score