Effects of acute bouts of aerobic exercise of varied intensity on subjective mood experiences in women of different age groups across time.

Cox, Richard H. ; Thomas, Tom R. ; Hinton, Pam S. 等

In this investigation, the focus is upon the effects of an acute bout of aerobic exercise upon positive and negative affect as measured by McAuley and Courneya's (1994) exercise specific Subjective Exercise Experiences Scale (SEES). Other inventories that have been used to study the effects of exercise upon positive and negative affect include: Gauvin and Rejeski's (1993) exercise specific Exercise-Induced Feeling Inventory (EFI), the Profile of Mood States (POMS; McNair, Lorr & Droppleman, 1992), Watson, Clark and Tellegen's (1988) Positive and Negative Affect Schedule (PANAS), and the Revised Multiple Affect Adjective Checklist (MAACL-R; Zuckerman & Lubin, 1985).

Berger and Motl (2000) reviewed 25 investigations in which the Profile of Mood States (POMS) was used to measure changes in mood associated with acute bouts of aerobic exercise and physical activity. The vast majority of results show decreases in tension, depression, anger, and confusion associated with acute bouts of moderate intensity exercise. Moderate intensity exercise may not optimize fitness and sport training benefits, but it has consistently been associated with desirable mood changes (Berger & Owen, 1988; Motl, Berger & Wilson, 1996; Tuson, Sinyor, & Pelletier, 1995). Conversely, high intensity exercise has been linked with either no mood changes or undesirable mood changes (Motl et al., 1996; Steptoe & Cox, 1988). Results obtained when using the POMS are generally consistent with those obtained with other instruments such as the EFI and SEES (Treasure & Newberry, 1998; Szabo, Mesko, Caputo & Gill, 1998).

From this brief review of the literature, it would appear that a moderate bout of exercise is superior to either a high or low bout of aerobic exercise for reducing negative affect and increasing positive affect. However, a closer examination is warranted. In the negative affect literature (state anxiety), the notion that high intensity exercise leads to an increase in state anxiety comes primarily from a study reported by Steptoe and Cox (1988). This research was flawed, however, in that exercise intensity was ascertained and manipulated using absolute as opposed to relative workloads. More recently, Cox, Thomas, Hinton and Donahue (2004) manipulated exercise intensity using relative workloads and observed that a high intensity bout of exercise was more effective than a moderate bout in reducing state anxiety in women. The notion that a moderate bout of aerobic exercise is superior to a more intense bout of exercise, in terms of mood modification, was also questioned by research reported by Blanchard, Rodgers, Wilson and Bell (2004). Blanchard et al. (2004) observed that both moderate and intense bouts of aerobic exercise are equally effective in increasing positive well-being and decreasing psychological distress when total volume of work between exercise conditions is equated. Furthermore, in a longitudinal study involving chronic exercise of older adults it was observed that a decrease in exercise intensity across an eight year period was associated with increased depression (Lampinen, Heikkinen & Ruoppila, 2000). These studies question the conventional wisdom that a moderate bout of aerobic exercise is always superior to a more intense bout of exercise. In the current investigation we manipulated exercise intensity as a percent of measured aerobic capacity, as opposed to either an estimate of aerobic capacity or as perceived exercise intensity.

Another important variable that has been studied in the anxiety literature is the notion of a delayed anxiolytic effect. In a study reported by Cox, Thomas, and Davis (2000) it was observed that a moderate or high intensity bout of aerobic exercise did not result in an immediate reduction in state anxiety, but 30 and 60-min following exercise it did. This delay in a reduction in anxiety following a bout of exercise was also observed by Raglin, Turner, and Eksten (1993), Raglin and Wislon (1996) and Cox et al. (2004). A similar effect has not been observed or studied systematically for positive affect. In the current investigation, positive and negative affect are measured up to 90-min post exercise. Because of the similarity between psychological distress and state anxiety it is logical to expect that a similar delayed reduction in psychological distress might occur following exercise.

Variables that have not been adequately studied, relative to positive and negative mood, include age of exerciser and the influence of iron deficiency in female exercisers. Berger, Owen, Mott and Parks (1998) identified age differences as an important independent variable that should be investigated. In the present investigation we included age in the model because we reasoned that older women might respond differently to exercise in terms of mood response. This reasoning was based upon a meta-analysis reported by Petruzzello, Landers, Hatfield, Kubitz and Salazar (1991). In their meta-analysis they observed that the effect size for individuals between the ages of 31-45 was nearly twice as large as for exercisers 18-30 years of age. Also, Cox et al. (2004) reported an interaction between age and exercise intensity after controlling for iron status.

While direct evidence relating iron status to mood is sparse, the biological consequences of iron deficiency may affect mood changes associated with exercise. Iron deficiency results in decreased performance during aerobic exercise (Haas & Brownlie, 2001; Beard, 2001), and in alterations in neurotransmitter systems (Beard, 2001). Furthermore, iron deficiency, determined by low hematocrit (Hct) and hemoglobin (Hb) and by depleted iron stores, i.e., low serum ferritin (sFer) is common in women of reproductive age (Looker, Dallman, Carrol, Gunter, & Johnson, 1997). In this investigation, these hematological variables were taken into consideration to control for iron status and to assess any impact that iron status may have on psychological mood.

The purpose of the present investigation was to study the effects of an acute bout of aerobic exercise on the positive and negative affect of women of different ages, while controlling for iron status. Manipulated independent variables included intensity of exercise, age of participant, and time of measurement. The dependent variables in this investigation were fatigue, psychological distress, and positive well-being. Research hypotheses included the following:

1. Moderate and high intensity bouts of acute aerobic exercise will be superior to a control group in terms of improving perceived fatigue, psychological distress, and psychological well-being.

2. An exercise intensity of 60% V[O.sub.2] max (moderate) will be more effective than an exercise intensity of 80% of V[O.sub.2] max (high) in terms of modifying psychological affect.

3. A delayed psychological distress reduction effect will be observed for moderate and high intensity bouts of aerobic exercise.

4. After controlling for iron status, age of participant alone or in combination with exercise intensity and/or time of measurement will differentially modify positive and : negative affect.

Method

Participants

Participants for the study were 24 active Caucasian females. Participants were recruited according to age and were categorized into 18-20 year (n=12) or 35-45 year (n=12) groups. Active was defined as being in good physical health and participating in cardiovascular exercise at least three times a week for 20-min or more each day. Potential participants were not accepted if competing for an intercollegiate team, or if training for a long distance run of greater than ten miles. Because criteria for selection were included in all pre-study announcements, no prospective participants were turned away. Participants were informed of the risks associated with the study and were required to complete an informed consent form approved by the campus human subjects IRB. Each participant was paid $52.50 to serve as a research subject. Participant characteristics are displayed in Table 1.

Measures

Positive and negative psychological affect. Psychological affect associated with exercise was assessed using McAuley and Courneya's (1994) Subjective Exercise Experiences Scale (SEES). The SEES is a 12-item inventory (7-point Likert scale) which measures positive well-being, psychological stress, and fatigue. In completing the inventory, participants were asked to respond to the items according to how they feel "now, at this point in time." In terms of internal reliability, McAuley and Coumeya (1994) reported alpha coefficients of .84 to .92 for the three subscaleS. With respect to convergent validity, the SEES subscales display moderately high correlations (.6 to .7) with other scales that measure positive and negative affect. At the same time that participants completed the SEES, they also completed Spielberger's (1983) State-Trait Anxiety Inventory (STAI; Form Y-1). Results of research associated with the state anxiety data are reported elsewhere (Cox, Thomas, Hinton & Donahue, 2004).

Perceived exertion and heart rate. Perceived exertion was measured using Borg's Rating of Perceived Exertion (RPE) scale (Borg, 1977), which requires participants to rate, on a 6 to 20 point category scale, their perceptions of exertion during exercise. Participants were asked to provide ratings of perceived exertion at the 15, 20, 25, and 30-min points of a 33-min bout of acute exercise. Measurement of perceived exertion was used to provide a manipulation check for intensity of exercise. Heart rate was measured using a Polar Vantage Heart Rate Monitor and recorded at the 0, 15, 20, 25, 30, and 33-min points of the 33-min exercise bout. HR was also used to provide a manipulation check of intensity of exercise. Concurrent validity of the RPE scale has been determined by correlating RPE scores with heart rate (HR) and other measures of physiological exertion. Borg (1982) reported correlations of .80 to .90 between RPE scores and HR. Test-retest and intra-class reliability coefficients of .78 to .83 have also been reported (Noble & Robertson, 1996).

Blood collection. Blood was collected from a butterfly needle inserted into an antecubital vein. All blood samples were collected into 7 ml tubes containing EDTA (anticoagulant and chelating agent). All samples were separated by centrifugation at 4[degrees]C for 15-min at 2000g in a Marathon 22100R centrifuge (Fisher Scientific, Pittsburgh, PA). The separated plasma was transferred to 1.8 ml cryogenic vials and stored at -70[degrees]C for later analysis. Hematocrit (Hct) was measured immediately following each blood draw using the microhematocrit method. Hemoglobin (Hb) measurements were also completed immediately following each blood draw using a standard diagnostic kit (Procedure #525, Sigma Diagnostics, St. Louis, MO). Using the commercially available ELISA kit (Catalog #S-22, RAMCO Labortories, Stafford, Texas), serum ferritin (sFer) measurements were completed using stored plasma samples.

Procedures

Orientation and screening. During a potential participant's initial visit, the individual was informed about the purpose of the research. If the individual agreed to participate, they were required to complete a health history questionnaire and a prospective screening questionnaire. In order to control for mood, an additional medical questionnaire identifying the proliferative phase of their menstrual cycle was completed. The proliferative phase (10 days post menstruation) was the window of time utilized to perform all submaximal exercise sessions, but not necessarily the V[O.sub.2] max test. At the time of the initial screening, blood was collected to determine Hct, Hb, and sFer concentrations. Prospective participants were excused if they were being treated for high blood pressure, epilepsy, eating disorders, psychological disorders; or if they possessed more than one cardiovascular disease (CVD) risk factor as defined by the American College of Sports Medicine (ACSM; 2000) or any disease symptoms. Percent body fat was determined using skin-fold calipers and the measurement of skinfolds at three body sites after the method of Jackson, Pollock, and Ward (1980). Participants were informed that when they report for V[O.sub.2]max testing, they should abstain from food and beverages (except water) for three hours prior to testing, and abstain from exercise for a period of 48 hours prior to testing.

Maximal aerobic capacity. Maximal aerobic capacity was determined through an incremental exercise test on a Quinton treadmill (Model 18-60). The results of each V[O.sub.2] max test determined the appropriate exercise intensity to be used during the subsequent submaximal exercise sessions. Initially, participants warmed up at a walking speed of 3.0 mph. Following the warm-up, the speed of the treadmill was set at 4.0 mph for 2-min. Speed was increased 0.5 mph every min until reaching 6.5 mph. Following this time point, the grade of the treadmill was increased 2.0% every min at 6.5 mph until the test was completed. Expired gases were monitored using a metabolic cart. The point of V[O.sub.2] max was determined using the following criteria: volitional exhaustion, a respiratory exchange ratio higher than 1.1, and a plateau in oxygen consumption. Following V[O.sub.2] max testing, appointments were made for each participant to return for their first sub-maximal exercise test. Furthermore, they were asked to abstain from food and beverages (except water) for two hours prior to testing, and abstain from exercise for a period of 24 hours prior to testing.

Submaximal exercise testing. Approximately one week after the V[O.sub.2]max testing, each participant returned to the Exercise Physiology Laboratory (EPL) for the first of three experimental sessions consisting of a control and two exercise sessions. Each session was separated by approximately 48 hours, and all three sessions were scheduled within the participant's self-determined proliferative phase of her menstrual cycle. For all three experimental sessions, when the participant first entered the EPL, she was asked to sit down at a table and complete the SEES. Because all participants had previously completed a V[O.sub.2] max test, they were sufficiently habituated to the laboratory and to the operation of the treadmill.

Following psychological testing, participants were prepared for exercise at their assigned intensity for that day (or control). Participants either did not exercise (control condition) or exercised at 60% or 80% of V[O.sub.2] max for 33-min according to a predetermined randomly assigned diagram balanced Latin square (Wagenar, 1969). Counterbalancing the presentation of experimental conditions was used to control for systematic carry over effect due to order (Kepple, 1991). While in the control condition, participants were treated identical to other conditions, with the exception that they sat quietly for 33-min on a chair placed on the treadmill instead of exercising. While sitting on the chair, participant's HR was monitored and she was connected to a metabolic cart as if actually exercising. Control participant's perceived exertion was not monitored or requested.

During submaximal exercise sessions, participants began by wanning up for 2-min at 3.0 mph. The following 8-min were used to slowly increase the speed of the treadmill until the participant was near their randomly assigned target range of 60% or 80% V[O.sub.2] max as determined from V[O.sub.2] max data. Once this was achieved, participants ran for 20-min at their target intensity. Following the 20-min at the target intensity, the participant was allowed to walk for three minutes in order to cool down. The total time of the submaximal exercise bouts was 33-min. Perceived exertion and HR were recorded at the 15, 20, 25, and 30-min point of the exercise bout. Heart rate was also recorded at the 0 and 33-min points.

Post experimental session. Following the 33-min bout of aerobic exercise (or control), participants were again seated at a table and asked to complete the SEES. The SEES was administered approximately 5-min after cessation of exercise, and again at 30, 60, and 90-min after cessation of exercise. All administrations of the SEES took place in a quiet room adjacent to the exercise testing room, but still in the EPL. This was the same quiet room in which the preexercise measurement of mood was taken. During the time the participants were relaxing they were offered cool water and allowed to dry off and to read while sitting at a table. Reading material included back issues of the National Geographic Explorer and Better Homes and Gardens. Each participant completed the SEES five times within each exercise intensity condition, for a total of 15 times.

Data Analysis

As a manipulation check for intensity of exercise, an age by intensity by time (2x3x4) ANOVA on HR and an age by intensity by time (2x2x4) ANOVA on RPE was conducted. A significant main effect for intensity was expected for both HR and RPE. This outcome would verify that manipulation of V[O.sub.2] max was effective in changing exercise intensity.

Perceived fatigue, psychological distress and positive well-being were each analyzed using separate age by intensity by time (2x3x5) analysis of covariance (ANCOVA) procedure with repeated measures on the intensity and time variables. Both hemoglobin (Hb) and serum ferritin (sFer) served as covariates in the models. Interactions were interpreted by studying the simple effects of one variable at different levels of a second variable (Kepple, 1991). Planned comparisons, involving the time effect, included contrasts between baseline measures of psychological affect and all other times, and four trend contrasts (linear, quadratic, cubic, quartic).

All main effects, simple effects, and mean comparisons were interpreted using a type 1 error rate of .05 (alpha). Probability level of effects involving repeated measures were corrected for violations of sphericity as outlined by Huynh and Feldt (1970). Effect sizes were reported using partial Eta-square ([eta.sup.2] p) as recommended by Tabachnick and Fidell (2001, p. 52). Etasquare represents effect size as a function of total variance accounted for by the independent variable.

Results

Data Screening

Prior to data analyses, all data were screened for outliers and means and standard deviations were scrutinized. This process revealed a skewness index of 2.00 and a kurtosis index of 3.54 for serum ferritin (sFer). Using 2.00 as a reasonable criterion and observing that the variance for the older women was 14 times larger than the variance for the younger women (see Table 1), a decision was made to transform sFer scores to log10. The skewness and kurtosis indices for the transformed sFer scores were .69 and .20 respectively. Furthermore, it was observed that the correlation between Hct and Hb was .80. Because these two variables were highly correlated, only Hb and Sfer were entered into the ANCOVA model as covariates (Tabachnick & Fidell, 2001). The correlation between participant's overall SEES scores with Hb and sFer was .08 and .30 respectively for perceived fatigue, .25 and .03 respectively for psychological distress, and. 11 and .02 respectively for psychological well-being; suggesting that the covariates will have minimal effect on the dependent variables. As part of the ANCOVA procedure, tests were conducted to verify that an interaction was not present between the grouping variable (age of participant) and the covariates.

Exercise Intensity Manipulation Check

The ANOVA on HR revealed significant main effects for age, intensity, and time; as well as significant interactions between intensity and age, and between intensity and time. Not-with-standing the complexity of significant interactions, plotting and testing of main and simple effect means revealed significant differences in heart rate as a function of intensity manipulation. Higher HR was associated with higher exercise intensity. Similarly, the ANOVA on RPE revealed significant effects for the main effects of intensity and time; as well as a significant intensity by time interaction. Plotting and testing of simple effect means revealed significant differences in perceived exertion as a function of intensity manipulation. Higher RPE was associated with higher exercise intensity.

Analysis of Covariance on SEES Subscales

Fatigue. The three factor ANCOVA on fatigue yielded a significant main effect for time, F(4, 80) = 4.07, p = .01, [[eta].sup.2] p =. 17. No other main effects or their interactions were significant at the .05 level. Planned contrasts between baseline and all other measurement times revealed a significant difference between baseline and when fatigue was measured 90-min post exercise (p=.02, [[eta].sup.2] p = .25). Additionally, a planned trend analysis revealed significant linear (p=.01, [[eta].sup.2] p = .27) and quartic trends (p=.005, [[eta].sup.2] p = .33). The means and standard deviations for the five fatigue scores across time were as follows: 7.75 [+ or -] 4.00, 8.69 [+ or -] 4.83, 7.25 [+ or -] 3.58, 7.31 [+ or -] 4.10, 6.40 [+ or -] 3.54.

Psychological distress. The three factor ANCOVA on psychological distress yielded a significant main effect for time, F(4, 80) = 8.58, p = .001, [[eta].sup.2] p = .30, and a significant intensity by age interaction, F(2, 40) = 4.25, p = .03, [[eta].sup.2] p =. 17. No other main effects or their interactions were significant at the .05 level. Collapsing across age of participant and exercise intensity, planned comparisons between baseline and all other measurement times revealed a significant difference between baseline and when psychological distress was measured 5-min (p=.05, [[eta].sup.2] p = 18), 30-min (p= .00,3, [[eta].sup.2] p = .36), 60-min (p=.001, [[eta].sup.2] p =.42), and 90-min (p=.004, [[eta].sup.2] p =.35)post exercise. Additionally, a planned trend analysis revealed significant linear (p=.001, [[eta].sup.2] p =.43) and quadratic trends (p=.01, [[eta].sup.2] p =.28). The means and standard deviations for the five psychological distress scores across time were as follows: 5.53 [+ or -] 2.64, 4.76 [+ or -] 1.43, 4.38 [+ or -] 1 04, 4 72 [+ or -] 1 48, and4.19 [+ or -] 0.62.

The nature of the interaction between age of participants and exercise intensity was studied by plotting cell means; and by testing for simple effects of intensity at the two different levels of age, and simple effects of age at the three different levels of exercise intensity. The plotting of means suggested that a difference might exist (a) between the younger and older participants in the control condition, and (b) between the control group and the exercise conditions in the older participants. However, none of the simple comparisons or simple ANOVA's revealed significant differences between age groups or among exercise intensities at the .05 level. Actual means and standard deviations are displayed in Table 2.

Positive well-being. The three factor ANCOVA on positive well-being yielded a significant main effect for intensity, F(2, 40) = 18.7, p = .0001, [[eta].sup.2] = .48, and for the intensity by time by age interaction, F(8, 160) = 2.31, p = .03, [[eta].sup.2] =. 10. No other main effects or their interactions were significant at the .05 level. The significant triple interaction suggests that the intensity by time interaction for the younger participants is different than the same interaction for the older participants. As a first step in interpreting the triple interaction, separate intensity by time ANOVA's were calculated for the younger and older participants separately.

The intensity by time (3 x 5) repeated measures ANOVA for the younger participants resulted in a significant intensity main effect, F(2, 22) = 7.02, p = .004, [[eta].sup.2] = .39, but insignificant effects for the time and the intensity by time interaction. The nature of the insignificant intensity by time interaction for the younger participants is illustrated in Figure 1 and Table 3. While it appears that a difference exists among the exercise conditions at baseline, this was not verified statistically (p=. 12, [[eta].sup.2] p =. 18). Collapsing across time, comparisons among exercise intensity means revealed a significant difference between the control condition and the 80% V[O.sub.2]max condition (p=.005, [[eta].sup.2] p =.53), and between the 60% V[O.sub.2], max condition and the 80% V[O.sub.2] max condition (p=.03, [[eta].sup.2] p =.36). Means and standard deviations for the control, 60% V[O.sub.2]max and 80% V[O.sub.2]max conditions were 18.30 [+ or -] 6.02, 19.37 [+ or -] 5.26 and 21.02 [+ or -] 5.33 respectively.

The intensity by time (3 x 5) repeated measures ANOVA for the older participants resulted in a significant intensity main effect, F(2, 22) = 11.59, p = .0005, [[eta].sup.2] p =.51, and a significant intensity by time interaction, F(8, 88) = 3.31, p = .005, [[eta].sup.2] p = .23. The nature of the significant intensity by time interaction for the older participants is illustrated in Figure 2 and Table 3. The exercise intensity by time interaction was interpreted by looking at the simple effects of intensity at the five different time periods, and by looking at the simple main effects of time at the three different levels of exercise intensity.

Relative to the simple effects of exercise intensity at the different levels of time, all effects were significant except for the simple effect of intensity at time 1. At time 2, significant mean comparisons were observed between control and the 60% condition (p=.02, [[eta].sup.2] p =.39) and between control and the 80% condition (p=.002, [[eta].sup.2] p =.60). At time 3, significant mean comparisons were observed between control and the 60% condition (p=.004, [[eta].sup.2] p =.54) and between control and the 80% condition (p=.0001, [[eta].sup.2] p =.77). At time 4, significant mean comparisons were again observed between control and the 60% condition (p=.02, [[eta].sup.2] p =.40) and between control and the 80% condition (p=.003, [[eta].sup.2] p =.71). At time 5, significant mean comparisons were observed between control and the 60% condition (p=.025, [[eta].sup.2] p =.38) and between control and the 80% condition (p=.002, [[eta].sup.2] p =.74).

Relative to the simple effects of time at the different levels of exercise intensity, only the simple effect for the 80% V[O.sub.2]max condition was significant (p=.05, [[eta].sup.2] p =.21). For the 80% condition, significant or borderline significant differences (p=.06) were observed between time 1 (baseline) and time 2 (p=.06, [[eta].sup.2] =.28), time 1 and time 3 (p=.03, [[eta].sup.2] p =.38), and time 1 and time 5 (p=.06, [[eta].sup.2] p =.28). A significant cubic trend was also observed for the 80% condition, F(1, 11) = 5.01, p = .047, [[eta].sup.2] p =.31.

Discussion

Consistent with hypothesis one, moderate and high intensity bouts of acute aerobic were generally observed to be superior to a control group in terms of increased psychological well-being. However, in terms of post-exercise perceived fatigue and psychological distress, the results were not consistent with hypothesis one. Inconsistent with hypothesis two, a moderate bout of aerobic exercise was not superior to a high intensity bout of exercise for modifying psychological affect in a positive direction. No differences were observed between the two exercise intensities for fatigue and psychological distress, but for positive well-being it was observed that a high intensity condition was superior to a moderate intensity exercise condition for elevating positive affect. The implications of the results of this investigation are significant, in that they call in to question the conventional wisdom that an acute bout of moderate aerobic exercise is always superior to a more intense bout of exercise.

The main observation for fatigue was that it decreases across time following a 33-min bout of exercise, regardless of age of participant and exercise intensity (including the control group). It is easy to understand why the perception of fatigue (e.g. tired, drained) would dissipate following a vigorous bout of exercise of any intensity, but not for the control condition. Apparently, sitting on a treadmill for 33-min also makes one feel tired and fatigued (perhaps tired of sitting). Here, we conclude that fatigue associated with exercise and sitting dissipates across time regardless of exercise intensity.

As with fatigue, psychological distress decreased linearly and in a somewhat quadratic manner across time regardless of exercise intensity condition. In the absence of a control condition, it might have been concluded that moderate and high intensity exercise effectively reduces psychological distress (Cox et al., 2001). However, as the current investigation demonstrates, compared to a control group neither moderate or high intensity exercise reduces psychological distress. Related research has demonstrated that, 30-min post-exercise, state anxiety of high intensity exercisers decreases significantly below baseline compared to a control condition (Cox et al., 2004). From this we conclude that psychological distress as measured by the SEES is not the same as state anxiety as measured by Spielberger's STAI (1983).

Relative to positive well-being, the results clearly demonstrate the superiority of the two exercise intensity conditions over the control condition for both the younger (Figure 1) and older women (Figure 2). The results also suggest a superiority of the 80% V[O.sub.2] max exercise condition over the 60% V[O.sub.2] max condition in terms of elevating positive affect. This seems to be true despite the lack of a significant time by intensity interaction for the younger women. These results are consistent with Cox et al. (2004) and Blanchard et al. (2004), but inconsistent with an earlier study reported by Tuson et al. (1995). In this earlier study, differences between high and medium exercise intensities were not observed when considering exercise intensity as being a percent of estimated V[O.sub.2] max. However, when data were re-conceptualized as a function of perceived exertion, as opposed to actual manipulated intensity, the results suggested a superiority of the moderate perceived exertion group over the high exertion group.

Inconsistent with hypothesis three a delayed psychological distress effect was not observed following exercise. Relative to state anxiety, many previous investigations have reported a delayed effect in observing a reduction in anxiety following an acute bout of aerobic exercise (Cox et al., 2000, 2004; Raglin et al., 1993; Raglin & Wilson, 1996). That is, a reduction in anxiety was not observed for the exercise condition immediately after exercise, but appeared 30 to 60 min after exercise. No such effect was observed in the present investigation for psychological distress, providing further evidence that the SEES measure of psychological distress is different than state anxiety as measured by Spielberger's STAI.

Inconsistent with hypothesis four, after controlling for iron status, significant main effects were not observed between the two age groups for any of the SEES subscales. Organized as a function of age, total adjusted means and total actual means and standard deviations for each SEES subscale are displayed in Table 1. After controlling for iron status, only two interactions involving age (grouping variable) were observed to be significant. These were the age by intensity interaction for psychological distress and the age by intensity by time interaction for positive well-being. In the case of the triple interaction for positive well-being, the simple interactions between the two repeated measures (intensity & time) are displayed separately for the younger and older women in Figures 1 and 2. These two figures show how psychological well-being varies across time and exercise intensity for the different age groups. From these figures it appears that, compared to a control condition, the two exercise conditions result in increased positive well-being. The exact nature of these relationships differs as a function of age of participant.

Compared to the control group, acute bouts of aerobic exercise had little effect upon fatigue or psychological distress, but a beneficial effect upon positive well-being. This conclusion is particularly true for the 80% V[O.sub.2] exercise condition. It is unlikely that controlling for iron status had more than a minor effect on the outcome of this research. This conclusion is based on the observation that iron status and total SEES subscales were poorly correlated, and the observation that actual means and adjusted means associated with the between subject variable (age) were nearly identical. Nevertheless, because of the potential mood effect that iron status may have upon women of different ages it is recommended that this line of inquiry continue. The triple interaction between age, exercise intensity, and time for positive well-being was intriguing. This interaction suggests that age of female participant may be an important moderator variable for understanding the relationship between positive and negative mood at different levels of exercise intensity and across time. While mode of exercise was not utilized as an independent variable in this investigation, it is recommended that it be included in future research. This is based on two previous investigations that suggested that mode of exercise may also have a moderating effect upon the relationship between affect and exercise intensity (Cox,Thomas & Davis, 2001; Thomas, Londeree, Lawson, Ziogas & Cox, 1994).

While great care was taken in developing a carefully controlled investigation, we may have created some circumstances that could be considered limitations. For example, sitting quietly on a treadmill for 33-min may have been stressful for some participants and may have negatively affected mood scores. Similarly, spending 90-min in a laboratory situation following exercise may have been very different than doing the same thing following no exercise. Another limitation to the study might be the controlled nature of the exercise environment. Exercising in a laboratory on a treadmill is not the same as exercising in a naturalistic environment.

Authos Note

This research was supported in part by an internal Research Council Grant from the University of Missouri-Columbia.

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Richard H. Cox, Tom R. Thomas, Pam S. Hinton, and Owen M. Donahue

University of Missouri--Columbia

Address Correspondence To: Richard H. Cox, Department of ESCP, 16 Hill Hall, University of Missouri-Columbia, Columbia, MO 65211, [email protected], Phone:573-882-7602 Fax: 573-884-5989

Table 1
Participant Characteristics Grouped as a Function of Group (values are
means [+ or -] s.d.)

Group Younger Women Older Women

Age 18.6 [+ or -] 0.7 * 40.2 [+ or -] 3.4
Height (cm) 164 [+ or -] 6.4 168 [+ or -] 5.0
Weight (kg) 57.5 [+ or -] 6.9 * 63.1 [+ or -] 5.9
% Body Fat 22.7 [+ or -] 4.4 22.6 [+ or -] 5.8
V[O.sub.2]Max 42.3 [+ or -] 4.3 * 36.2 [+ or -] 5.3
 (ml/kg/min)
Hemo-globin (Hb) 13.3 [+ or -] 1.3 13.3 [+ or -] 1.3
Serum Ferritin 13.9 [+ or -] 5.0 * 28.9 [+ or -] 19
 (sFer)
SEES Fatigue 7.8 [+ or -] 2.2 (7.4) # 7.2 [+ or -] 2.2 (7.6)
SEES Distress 4.6 [+ or -] 0.9 (4.7) 4.7 [+ or -] 0.8 (4.6)
SEES Well-being 19.6 [+ or -] 5.3 (19.5) 20.0 [+ or -] 2.9 (20.0)

* Indicates significant difference between means in the column (p <.05)

# Adjusted SEES subscale means

Table 2
Actual Means and Standard Deviations (in parentheses) Associated with
the Intensity by Age Interaction for Psychological Distress

 Exercise Intensity

Age of Participant Control 60%V[O.sub.2]max 80%V[O.sub.2]max

Younger Women 4.60 4.63 4.68
 (0.91) (1.24) (1.17)

Older Women 5.23 4.35 4.50
 (1.80) (0.45) (0.53)

Table 3
Gender by Intensity by Time Interaction Means and Standard Deviations
(in parentheses) Associated with Positive Well-being.

Age Younger Women

Intensity Control 60%V[O.sub.2]max 80%V[O.sub.2]max

Time

Baseline (T1) 18.17 18.00 20.58
 (05.87) (05.01) (04.58)

+05 Min (T2) 18.58 19.83 21.33
 (05.88) (05.78) (06.18)

+30 Min (T3) 17.92 19.25 21.33
 (06.16) (05.35) (05.07)

+60 Min (T4) 18.25 19.83 20.33
 (06.45) (05.42) (05.63)

+90 Min (T5) 18.58 19.92 21.50
 (06.72) (05.38) (05.89)

Age Older Women

Intensity Control 60%V[O.sub.2]max 80%V[O.sub.2]max

Time

Baseline (T1) 18.92 20.83 19.50
 (04.08) (04.65) (04.32)

+05 Min (T2) 17.75 21.08 22.10
 (03.49) (03.82) (02.39)

+30 Min (T3) 17.75 20.92 21.75
 (03.70) (03.06) (03.00)

+60 Min (T4) 17.92 20.25 21.25
 (04.03) (03.67) (03.25)

+90 Min (T5) 17.92 20.00 21.58
 (04.06) (03.30) (02.71)