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Effects of aerobic exercise training and relaxation training on cardiovascular activity during psychological stress
Journal
of Psychosomatic
Research.
Vol. 32, Nos 415, pp. 469-474,
W22-3999/88$3.00 + 00 0 1988Pergamon Press plc
1988.
Printed in Great Britain.
EFFECTS
OF AEROBIC
RELAXATION ACTIVITY
EXERCISE
TRAINING DURING
TRAINING
AND
ON CARDIOVASCULAR
PSYCHOLOGICAL
STRESS
DAVID S. HOLMES and DAVID L. ROTH (Received 30 June 1987; accepted in revised form 14 June 1988)
Abstract-Students who reported experiencing a high number of stressful life events were randomly assigned to: (a) an aerobic training condition, (b) a relaxation training condition, or (c) a no treatment control condition. Immediately before and after the 11 week training/control period, subjects’ aerobic fitness and cardiovascular responses to acute psychological stress were assessed. Results indicated that: (1) subjects in the aerobic training condition showed significantly greater improvements in aerobic fitness than subjects in the other conditions, and (2) the subjects in the aerobic training condition showed significantly greater reductions in heart rate during all phases of the stress than subjects in the other conditions. Post-training differences between aerobic and control conditions during the moderate psychological stress were as great as 17 b.p.m. These results provide evidence for the utility of aerobic training for reducing cardiovascular activity during psychological stress, and they are consistent with earlier findings linking fitness to less illness following stress, reductions in depression and enhanced recovery in cardiac patients.
INTRODUCTION THERE IS widespread concern over the cardiovascular effects of psychological stress [l], and the results of a variety of studies have indicated that the cardiovascular effects of stress may be more pronounced in persons who are in poor aerobic condition [2, 31. Because of this, a considerable amount of attention is being focused on the use of aerobic training as a strategy for improving a person’s response to stress. In considering the evidence concerning aerobic fitness and the cardiovascular response to stress, two important qualifications should be recognized. First, although there are numerous correlational studies linking higher levels of fitness to lower levels of cardiovascular response to stress, only two experiments have been reported in which aerobic fitness training programs were shown to be more effective than no treatment for reducing the cardiovascular response to stress [4,5]. Furthermore, in one of those experiments the training program was only effective for enhancing the recovery from stress rather than reducing the response to stress [4]. The second qualification that should be noted is that thus far there is no evidence concerning the effects of aerobic training relative to the effects of other types of interventions such as muscle relaxation training, imagery or selfmonitoring. In other words, at the present time we do not know whether aerobic training is more or less effective than other stress management programs. The present experiment was conducted to determine: (a) whether a brief aerobic training program was effective for reducing the cardiovascular response to stress, and (b) whether the aerobic training was more or less effective for reducing the
Department
of Psychology,
University
of Kansas, 469
Lawrence,
KS 66045,
U.S.A
DAVIII S. HOLMES and DAVIS L. ROTH
470
response to stress than was a stress management program that involved muscle relaxation, imagery and self-monitoring. In this experiment, persons who were identified as recently experiencing high levels of life stress were: (a) tested for pretreatment levels of aerobic fitness; (b) exposed to a pre-treatment psychological stress while their cardiovascular responses were monitored; (c) given 11 weeks of aerobic exercise training, 11 weeks of relaxation training, or no treatment; (d) tested for post-treatment levels of aerobic fitness; and, finally, (e) again exposed to the stress while cardiovascular responses were monitored. METHOD Subjects The subjects were 49 undergraduate students who were drawn from a pool of over 1000 students on the basis of the high number of negative life events (mean percentile rank = 92) they reported for the preceding year on the Life .!Gperience.s Srtrvey [6]. These subjects were not already participating regularly in programs involving aerobic exercise or structured relaxation training. The subjects were randomly assigned to the exercise training (n = 17). relaxation training (n = 18) and no treatment (n = 14) conditions. (Sixteen other subjects began the project but withdrew during the first few weeks; 6, 3 and 7 from the three conditions, respectively.) Fifness festing Before and after the treatment period, each subject participated in a submaximal Balke treadmill test 17, 81. After being weighed and having his/her baseline heart rate and blood pressure assessed, the subject began walking on a motorized treadmill at a speed of 3.4 mph. Heart rates were monitored continuously using a Quinton electrocardiogram monitoring system, and the elevation of the treadmill was increased by 1% each minute. When the grade reached 100/o, an exercise heart rate and blood pressure was recorded, and then the test was continued until the subjects’s heart rate reached 90% of the predicted maximum. The grade at which the subject’s heart rate reached 90% of the predicted maximum was used to provide the estimate of aerobic capacity. Psychological stress test Before and after the treatment period, each subject participated in a laboratory session that involved a psychological stressor. All of the instructions for the session were provided by a tape recording, and the experimenter monitored each subject’s heart rate and blood pressure with a Narco Bio-Systems polygraph in an adjacent control room. The subiect was first asked to sit auietlv and relax for 5 min. This period was used to allow the subject to adjust to the situation and enable the experimenter to obtain p&stress (baseline) measures of heart rate and blood pressure. After the pre-stress period, the subject was told that he/she would be administered a memory subtest from a widely used test of intelligence, and that it was important for him/ her to do as well as possible on the test. The subject was then told that in this test he/she would be read six series of numbers, that each series would contain five numbers, and that after each series was read his/her task was to repeat the numbers backwards. After the instructions were completed, six series of five numbers were read to the subject, and sufficient amounts of time were provided between each series to allow the subject to respond. The subject was allowed to sit quietly for approximately 2 min after the conclusion of the test, and was then excused. Heart rate and blood pressure were assessed: (a) at the end of the pre-stress period; (b) immediately following problems I, 3 and 6; and (c) after a 45 set recovery period. 3
Treatments Aerobic exercise training. The subjects in the exercise condition met for 30 min sessions, 3 days per week (M, W, F), for 11 weeks. Exercise consisted of jogging (and brisk walking when necessary) on a one-eighth mile indoor track with a synthetic surface. In each session, exercise was preceded and followed by stretching to facilitate warm-up and cool-down. Each subject was initially given an exercise prescription that was based on his/her fitness level as determined by the Balke treadmill test. The prescription was given in terms of the lap pace that was necessary to achieve a heart rate that was approximately 75% of his/her predicted maximum heart rate. For most subjects, this target heart rate was approximately 150 b.p.m., and each subject was trained to monitor his/her own heart rate while exercising. Approximately half-way through the training period, the emphasis was changed from monitoring
Exercise
and stress
471
exercise intensity to monitoring distance. By the end of training, almost all of the subjects had run continuously for at least 2 miles. A total of 29 training sessions were held, and subjects participated in an average of 23.1 sessions. Progressive relaxation training. Subjects in the relaxation condition met for 30 min sessions, 3 days per week (M, W, F), for 11 weeks. In the first several sessions, the subjects participated in an abbreviated version of Jacobson’s [9] progressive muscle relaxation training procedure [lo]. Gradually, more abbreviated instructions for the muscle relaxation were used and other techniques, such as mental imagery [ll], were introduced and practiced. As training progressed, individual flexibility in the utilization of the various techniques was encouraged. The subjects were also taught how to monitor their heart rates, and they were told that a decrease in heart rate during relaxation is usually desirable because it indicates the removal of unnecessary physiological activity. A total of 29 relaxation training meetings were held, and subjects participated in an average of 24.8 meetings. No freafment. The subjects in the no treatment condition were not seen between the pre- and post-tests of fitness and response to psychological stress.
RESULTS
Influence of training on fitness An analysis of covariance that was conducted on the post-treatment estimated oxygen consumption scores derived from the treadmill test revealed a significant difference among conditions, F(2,43) = 8.65, p = 0.0007. (The covariate in this and subsequent analyses of covariance was the set of pre-treatment scores for the variable under consideration, thus the potential influence of initial differences was eliminated [12].) Pairwise comparisons of the adjusted means indicated that after training subjects in the exercise condition achieved significantly higher levels of aerobic fitness (as measured by estimated oxygen consumption) than did the subjects in the relaxation or no treatment conditions, Fs (1,43) = 10.82 and 14.13, ps = 0.002 and 0.0005, respectively. Adjusted means = 49.6, 45.8, 45.3 ml/kg/min, respectively. Evaluation of changes from pre- to post-treatment levels indicated that subjects in the exercise condition showed a 10% improvement in estimated oxygen consumption. An analysis of covariance conducted on subjects’ posttreatment heart rates at the 10% treadmill grade also revealed a significant difference among the conditions, F (2,43) = 6.66, p = 0.003. Pairwise comparisons indicated that, after training, the subjects in the exercise condition evinced significantly lower exercise heart rates than did subjects in the relaxation training or the no treatment conditions, Fs (1,43) = 10.59 and 6.99, ps = 0.002 and 0.01. Adjusted means = 135.2, 146.0 and 144.0 b.p.m., respectively. Evaluation of changes from pre- to post-treatment levels indicated that subjects in the exercise condition showed a 7% decrease in exercise heart rate. Analyses of covariance conducted on subjects post-treatment systolic and diastolic blood pressures at the 10% treadmill grade did not reveal significant differences among the conditions, Fs (2,43) = 2.08 and 0.31, ps = 0.14 and 0.73, respectively. From these results it can be concluded that relative to relaxation training or no treatment, the exercise training was effective in improving subjects’ aerobic fitness as measured by estimated oxygen consumption and exercise heart rate, but it did not influence exercise blood pressure. The pre- to post-treatment changes in estimated oxygen consumption and exercise heart rate evinced by subjects in the exercise condition are comparable to those in other exercise training programs.
472
DAVID S. HOLMES and DAVID L. ROTH
Influence of training on cardiovascular activity during psychological stress A 3 conditions (exercise, relaxation, no-treatment) by 5 trials (pre-stress, stress 1, stress 2, stress 3, recovery) analysis of variance with repeated measures was conducted on post-treatment heart rates scores that had been adjusted for the corresponding pre-treatment levels with a covariance technique (viz. residualized scores [13]). That analysis revealed a significant difference among conditions, F (2,46) = 5.93, p = 0.005. The mean adjusted heart rates of the subjects in the exercise, relaxation and no treatment conditions during the pre-stress, stress, and recovery periods of the post-treatment stress test are presented graphically in Fig. 1. Pairwise comparisons indicated that during every period the subjects in the exercise condition had significantly lower heart rates than did the subjects in the relaxation (ps = 0.009, 0.025, 0.025, 0.025, 0.010) and no treatment conditions bs = 0.015, 0.002, 0.0001, 0.006, 0.022). During no period did the subjects in the relaxation and no treatment conditions differ in terms of heart rate @s = 0.847, 0.384, 0.100, 0.598, 0.783). Inspection of Fig. 1 indicates that during the pre-stress, stress and recovery periods, the subjects in the exercise condition had mean heart rates that were 10.76, 13.94, 17.06, 12.42 and 10.14 b.p.m. lower than those of subjects in the notreatment condition. Similarly, the subjects in the exercise condition had mean heart rates that were 11.62, 9.94, 9.87, 9.86 and 11.29 b.p.m. lower than those of subjects in the relaxation condition. In addition to being statistically significant, the differences in heart rate are of considerable magnitude and are probably of clinical significance. The analysis of the heart rate data also revealed significant differences across periods (higher during the stress than pre-stress and recovery periods), F (4,184) = 81.45, p < 0.001, but the conditions by trials interaction was not significant, F (8,184) = 1.64.
105 NO-RX I
100
595
I RELAXATION
& p 90 2 k 85 2 I 80
75
I EXERCISE
A PRE
1
2
3
REC
FIG. I .-Post-treatment heart rates (adjusted for pre-treatment levels) during pre-stress period, three stress periods and recovery period for subjects in the exercise training condition. relaxation training condition and no treatment conditions.
Exercise
and stress
473
Similar analyses conducted on the systolic blood pressure scores revealed significant differences across periods (higher during the stress than pie-stress and recovery periods), F (4,180) = 35.28, p < 0.001, but did not reveal significant differences among conditions, F (2,45) = 2.33. or a significant conditions by trials interaction. F (8,180) = 0.67. Analyses conducted on the diastolic blood pressure scores revealed a comparable patterning of findings: periods F (4,164) = 6.13, p < 0.001; conditions F (2,41) = 0.80; interaction F (8,164) = 0.88. From these results it can be concluded that the exercise treatment was effective in reducing subjects’ pre-stress, stress and recovery heart rates relative to subjects who received relaxation training or no treatment.
DISClJSSION
The results of this experiment indicate that a brief aerobic exercise training program was effective for reducing subjects’ heart rate before, during and after moderate psychological stress. It is noteworthy that the exercise treatment reduced the stress heart rate by as much as 17 b.p.m. (a 15% reduction), thus suggesting that the effect may have been clinically significant as well as statistically significant. The magnitude of this reduction is also notable because: (a) it occurred in the context of what was only a moderate stress (remembering numbers and repeating them backwards), (b) it was achieved in healthy subjects who were already in fairly good physical condition (relatively disease-free, active college students with average levels of aerobic fitness). and (c) it was achieved with a relatively brief (29 sessions) intervention program. It may be that greater effects would be achieved in situations involving more stress, populations who are at greater risk, and/or a more intense treatment program. In considering these findings it should be noted that the aerobic exercise training did not reduce the subjects’ response to stress. but instead reduced the subjects’ resting heart rate and that reduction was carried forward to the stress period. The findings revealed an interesting parallel between the effects of the treatment on the cardiovascular responses during physical exercise and psychological stress. The treatment influenced the heart rate response during both exercise and psychological stress but not did not influence the blood pressure response during either exercise or psychological stress. It appears that a different or more intensive approach will have to be taken to influence blood pressure. Finally, the results of this experiment provide a bridge to earlier findings indicating that the more fit persons were less likely to experience health problems and depression following life stress [ 141, that fitness reduced the cardiovascular response to stress among persons with a family history of hypertension such that the fit persons responded like persons who did not have a family history of hypertension [15], that fitness training was related to reductions in depression [16, 171, and that fitness training facilitated cardiovascular and psychosocial recovery of cardiac patients [lS]. It appears that fitness may be a valuable prophylactic for dealing with stress. AcknowlrdRernmfs-Appreciation is due to Nancy Sheldon and Julie Phillips for their assistance with this project. The research was supported in part by a grant from the University of Kansas to David Roth.
473
DAL/III S. HOI.MFS and DAVIII L. ROT~I REFERENCES
I. 2. 3.
3.
6.
7.
IO.
ot A. P.svc’hologic~~l Fuctms in Cardiovascular Dismte. New York: Academic Press. HOLMES DS. Ro-IFI DL. Association ot aerobic fitness with pulse riite and subjective responses t. Pv~c~ho~h~.~iolo~~ (in press). SINYOR D, S(.HWAIIIZ SC. PFRONNL-I F. BRISSON S. SERAC;ANI,XNP. Aerobic fitness level and reactivity to psychosocial stress: physiological, biochemical. and subjective measures. Ps~hosor~~ Met/ I YXR: 45: 205-2 I?. SIVYOR D. GOL.DEN M. SILIN~UY. SERAGANIAN P. Experimental manipulation of aerobic fitness and the response to psychosocial stress: heart rate and self-report measures. f’,s~cho,~on~ ~Ved 1986; 48: 326337. H~I.MES D. McG~t.r F)’ B. Influence of;r brief aerobic training program on heart rate :rnd cuhjective rchp0nse to psychologic stresaar. PF~choson1 Mrrl lYX7; 49: 36&F-373. SARASON I<;. JOHNsoN JH. Sir GFL.JM. Assessing the impact of life ch:mges: development of the Life Experiences Survey. J C‘onsulr din P.syc’hol lY78: 46: Y32-‘$46. Co~so~_arro CF. Jof INVIN RE. PEC~)K,I LJ. Ph~siolngiccrl ille~~ucrcwr~~~rs ofMetuholtc Fwrcriom it7 M~rz. New York: McGraw-Hill. LONIXR~E HR. Circulorespiratory exercise perscription tables. In The Complrrc ErercUr Smw
Prcwriplion. P rowedings of (he 1078 At~nual Meeting oftheCenfrnl Strtte C’hnptcr c?f‘ihe American College of.Spor/.~ Mcdicinr (Edited by LONIIEREE RR) pp. 97-106. lY7Y. JAU)HSON E. Propwsive Helu.\-ation. Chicqo: University of Chicago Press. lY.18. B~ZRN~IIIN DA. GIV!:V BA. Progressive relaxation: abbreviated methods. In Principles arrd Pr’oclic‘c of .Slwv.s Mrrt~rrgerncvfr (Edited by Woot.rol K RL. LEIIRFR PM) pp. 3.140. New York:
Guilford
II. 12. 13.
Press, lYX1. A. In tllc M/,~tl’.\ EJ~: 7%~ Powr of frnagc~ry for Pervottrrl Enrichrwrrt. New York: Guilford Press, lY77. WILII~R J. Bkisimetric approach (law of initial values) to biological rhythms. Anr? N Y Accrd Sci 1962; 98: 121 I-1220. CRONBA(.H LJ. FURRY. L. How should we measure ‘change’-“or should we’? Psycho! Bull 1070; 54: LALARIJS
hX--80.
13. IS. 16. 17. It;.
ROII~ DL. HOI MES DS. Influence of physical fitness in determining the impact of stressful life events on physical :tnd psychological he:dth. P~,vc/~o.san~ Marl IYSS; 47: 163-173. Hot.~ts D. C;\r~o B. Prophylactic effect of aerobic fitness on cardiov:lscular Lrrousal :imong individuals with :1 family history of hypertension. J p.q~/~osonr Rrs lY87; 31: 601-605. MKAYK IL, Hoi MES DS. Influence of aerobic exercise on depression. .I Person rot P.sychol lYt;3: 46: 1142-I 147. R(TI H D, HOL~IF~ D. Influence ot acrclblc exercise training and retaxntion training on physicwl and pr)chologicnl he:llth following stressful life events. P.r~c~/~oso~n Mel/ lY87; 49: 355-365. ROVIARO S. Ho1 ML!, DS, HOI.M\I t.N RD. Influence of 3 cardi;lc rehabilitation program on the ci~rdiovilscuI;ir, pqchological. and \ocliil functioning of cardiac patients. .I hchrnfl izlcd lY83; 7: hlXl.
of Psychosomatic
Research.
Vol. 32, Nos 415, pp. 469-474,
W22-3999/88$3.00 + 00 0 1988Pergamon Press plc
1988.
Printed in Great Britain.
EFFECTS
OF AEROBIC
RELAXATION ACTIVITY
EXERCISE
TRAINING DURING
TRAINING
AND
ON CARDIOVASCULAR
PSYCHOLOGICAL
STRESS
DAVID S. HOLMES and DAVID L. ROTH (Received 30 June 1987; accepted in revised form 14 June 1988)
Abstract-Students who reported experiencing a high number of stressful life events were randomly assigned to: (a) an aerobic training condition, (b) a relaxation training condition, or (c) a no treatment control condition. Immediately before and after the 11 week training/control period, subjects’ aerobic fitness and cardiovascular responses to acute psychological stress were assessed. Results indicated that: (1) subjects in the aerobic training condition showed significantly greater improvements in aerobic fitness than subjects in the other conditions, and (2) the subjects in the aerobic training condition showed significantly greater reductions in heart rate during all phases of the stress than subjects in the other conditions. Post-training differences between aerobic and control conditions during the moderate psychological stress were as great as 17 b.p.m. These results provide evidence for the utility of aerobic training for reducing cardiovascular activity during psychological stress, and they are consistent with earlier findings linking fitness to less illness following stress, reductions in depression and enhanced recovery in cardiac patients.
INTRODUCTION THERE IS widespread concern over the cardiovascular effects of psychological stress [l], and the results of a variety of studies have indicated that the cardiovascular effects of stress may be more pronounced in persons who are in poor aerobic condition [2, 31. Because of this, a considerable amount of attention is being focused on the use of aerobic training as a strategy for improving a person’s response to stress. In considering the evidence concerning aerobic fitness and the cardiovascular response to stress, two important qualifications should be recognized. First, although there are numerous correlational studies linking higher levels of fitness to lower levels of cardiovascular response to stress, only two experiments have been reported in which aerobic fitness training programs were shown to be more effective than no treatment for reducing the cardiovascular response to stress [4,5]. Furthermore, in one of those experiments the training program was only effective for enhancing the recovery from stress rather than reducing the response to stress [4]. The second qualification that should be noted is that thus far there is no evidence concerning the effects of aerobic training relative to the effects of other types of interventions such as muscle relaxation training, imagery or selfmonitoring. In other words, at the present time we do not know whether aerobic training is more or less effective than other stress management programs. The present experiment was conducted to determine: (a) whether a brief aerobic training program was effective for reducing the cardiovascular response to stress, and (b) whether the aerobic training was more or less effective for reducing the
Department
of Psychology,
University
of Kansas, 469
Lawrence,
KS 66045,
U.S.A
DAVIII S. HOLMES and DAVIS L. ROTH
470
response to stress than was a stress management program that involved muscle relaxation, imagery and self-monitoring. In this experiment, persons who were identified as recently experiencing high levels of life stress were: (a) tested for pretreatment levels of aerobic fitness; (b) exposed to a pre-treatment psychological stress while their cardiovascular responses were monitored; (c) given 11 weeks of aerobic exercise training, 11 weeks of relaxation training, or no treatment; (d) tested for post-treatment levels of aerobic fitness; and, finally, (e) again exposed to the stress while cardiovascular responses were monitored. METHOD Subjects The subjects were 49 undergraduate students who were drawn from a pool of over 1000 students on the basis of the high number of negative life events (mean percentile rank = 92) they reported for the preceding year on the Life .!Gperience.s Srtrvey [6]. These subjects were not already participating regularly in programs involving aerobic exercise or structured relaxation training. The subjects were randomly assigned to the exercise training (n = 17). relaxation training (n = 18) and no treatment (n = 14) conditions. (Sixteen other subjects began the project but withdrew during the first few weeks; 6, 3 and 7 from the three conditions, respectively.) Fifness festing Before and after the treatment period, each subject participated in a submaximal Balke treadmill test 17, 81. After being weighed and having his/her baseline heart rate and blood pressure assessed, the subject began walking on a motorized treadmill at a speed of 3.4 mph. Heart rates were monitored continuously using a Quinton electrocardiogram monitoring system, and the elevation of the treadmill was increased by 1% each minute. When the grade reached 100/o, an exercise heart rate and blood pressure was recorded, and then the test was continued until the subjects’s heart rate reached 90% of the predicted maximum. The grade at which the subject’s heart rate reached 90% of the predicted maximum was used to provide the estimate of aerobic capacity. Psychological stress test Before and after the treatment period, each subject participated in a laboratory session that involved a psychological stressor. All of the instructions for the session were provided by a tape recording, and the experimenter monitored each subject’s heart rate and blood pressure with a Narco Bio-Systems polygraph in an adjacent control room. The subiect was first asked to sit auietlv and relax for 5 min. This period was used to allow the subject to adjust to the situation and enable the experimenter to obtain p&stress (baseline) measures of heart rate and blood pressure. After the pre-stress period, the subject was told that he/she would be administered a memory subtest from a widely used test of intelligence, and that it was important for him/ her to do as well as possible on the test. The subject was then told that in this test he/she would be read six series of numbers, that each series would contain five numbers, and that after each series was read his/her task was to repeat the numbers backwards. After the instructions were completed, six series of five numbers were read to the subject, and sufficient amounts of time were provided between each series to allow the subject to respond. The subject was allowed to sit quietly for approximately 2 min after the conclusion of the test, and was then excused. Heart rate and blood pressure were assessed: (a) at the end of the pre-stress period; (b) immediately following problems I, 3 and 6; and (c) after a 45 set recovery period. 3
Treatments Aerobic exercise training. The subjects in the exercise condition met for 30 min sessions, 3 days per week (M, W, F), for 11 weeks. Exercise consisted of jogging (and brisk walking when necessary) on a one-eighth mile indoor track with a synthetic surface. In each session, exercise was preceded and followed by stretching to facilitate warm-up and cool-down. Each subject was initially given an exercise prescription that was based on his/her fitness level as determined by the Balke treadmill test. The prescription was given in terms of the lap pace that was necessary to achieve a heart rate that was approximately 75% of his/her predicted maximum heart rate. For most subjects, this target heart rate was approximately 150 b.p.m., and each subject was trained to monitor his/her own heart rate while exercising. Approximately half-way through the training period, the emphasis was changed from monitoring
Exercise
and stress
471
exercise intensity to monitoring distance. By the end of training, almost all of the subjects had run continuously for at least 2 miles. A total of 29 training sessions were held, and subjects participated in an average of 23.1 sessions. Progressive relaxation training. Subjects in the relaxation condition met for 30 min sessions, 3 days per week (M, W, F), for 11 weeks. In the first several sessions, the subjects participated in an abbreviated version of Jacobson’s [9] progressive muscle relaxation training procedure [lo]. Gradually, more abbreviated instructions for the muscle relaxation were used and other techniques, such as mental imagery [ll], were introduced and practiced. As training progressed, individual flexibility in the utilization of the various techniques was encouraged. The subjects were also taught how to monitor their heart rates, and they were told that a decrease in heart rate during relaxation is usually desirable because it indicates the removal of unnecessary physiological activity. A total of 29 relaxation training meetings were held, and subjects participated in an average of 24.8 meetings. No freafment. The subjects in the no treatment condition were not seen between the pre- and post-tests of fitness and response to psychological stress.
RESULTS
Influence of training on fitness An analysis of covariance that was conducted on the post-treatment estimated oxygen consumption scores derived from the treadmill test revealed a significant difference among conditions, F(2,43) = 8.65, p = 0.0007. (The covariate in this and subsequent analyses of covariance was the set of pre-treatment scores for the variable under consideration, thus the potential influence of initial differences was eliminated [12].) Pairwise comparisons of the adjusted means indicated that after training subjects in the exercise condition achieved significantly higher levels of aerobic fitness (as measured by estimated oxygen consumption) than did the subjects in the relaxation or no treatment conditions, Fs (1,43) = 10.82 and 14.13, ps = 0.002 and 0.0005, respectively. Adjusted means = 49.6, 45.8, 45.3 ml/kg/min, respectively. Evaluation of changes from pre- to post-treatment levels indicated that subjects in the exercise condition showed a 10% improvement in estimated oxygen consumption. An analysis of covariance conducted on subjects’ posttreatment heart rates at the 10% treadmill grade also revealed a significant difference among the conditions, F (2,43) = 6.66, p = 0.003. Pairwise comparisons indicated that, after training, the subjects in the exercise condition evinced significantly lower exercise heart rates than did subjects in the relaxation training or the no treatment conditions, Fs (1,43) = 10.59 and 6.99, ps = 0.002 and 0.01. Adjusted means = 135.2, 146.0 and 144.0 b.p.m., respectively. Evaluation of changes from pre- to post-treatment levels indicated that subjects in the exercise condition showed a 7% decrease in exercise heart rate. Analyses of covariance conducted on subjects post-treatment systolic and diastolic blood pressures at the 10% treadmill grade did not reveal significant differences among the conditions, Fs (2,43) = 2.08 and 0.31, ps = 0.14 and 0.73, respectively. From these results it can be concluded that relative to relaxation training or no treatment, the exercise training was effective in improving subjects’ aerobic fitness as measured by estimated oxygen consumption and exercise heart rate, but it did not influence exercise blood pressure. The pre- to post-treatment changes in estimated oxygen consumption and exercise heart rate evinced by subjects in the exercise condition are comparable to those in other exercise training programs.
472
DAVID S. HOLMES and DAVID L. ROTH
Influence of training on cardiovascular activity during psychological stress A 3 conditions (exercise, relaxation, no-treatment) by 5 trials (pre-stress, stress 1, stress 2, stress 3, recovery) analysis of variance with repeated measures was conducted on post-treatment heart rates scores that had been adjusted for the corresponding pre-treatment levels with a covariance technique (viz. residualized scores [13]). That analysis revealed a significant difference among conditions, F (2,46) = 5.93, p = 0.005. The mean adjusted heart rates of the subjects in the exercise, relaxation and no treatment conditions during the pre-stress, stress, and recovery periods of the post-treatment stress test are presented graphically in Fig. 1. Pairwise comparisons indicated that during every period the subjects in the exercise condition had significantly lower heart rates than did the subjects in the relaxation (ps = 0.009, 0.025, 0.025, 0.025, 0.010) and no treatment conditions bs = 0.015, 0.002, 0.0001, 0.006, 0.022). During no period did the subjects in the relaxation and no treatment conditions differ in terms of heart rate @s = 0.847, 0.384, 0.100, 0.598, 0.783). Inspection of Fig. 1 indicates that during the pre-stress, stress and recovery periods, the subjects in the exercise condition had mean heart rates that were 10.76, 13.94, 17.06, 12.42 and 10.14 b.p.m. lower than those of subjects in the notreatment condition. Similarly, the subjects in the exercise condition had mean heart rates that were 11.62, 9.94, 9.87, 9.86 and 11.29 b.p.m. lower than those of subjects in the relaxation condition. In addition to being statistically significant, the differences in heart rate are of considerable magnitude and are probably of clinical significance. The analysis of the heart rate data also revealed significant differences across periods (higher during the stress than pre-stress and recovery periods), F (4,184) = 81.45, p < 0.001, but the conditions by trials interaction was not significant, F (8,184) = 1.64.
105 NO-RX I
100
595
I RELAXATION
& p 90 2 k 85 2 I 80
75
I EXERCISE
A PRE
1
2
3
REC
FIG. I .-Post-treatment heart rates (adjusted for pre-treatment levels) during pre-stress period, three stress periods and recovery period for subjects in the exercise training condition. relaxation training condition and no treatment conditions.
Exercise
and stress
473
Similar analyses conducted on the systolic blood pressure scores revealed significant differences across periods (higher during the stress than pie-stress and recovery periods), F (4,180) = 35.28, p < 0.001, but did not reveal significant differences among conditions, F (2,45) = 2.33. or a significant conditions by trials interaction. F (8,180) = 0.67. Analyses conducted on the diastolic blood pressure scores revealed a comparable patterning of findings: periods F (4,164) = 6.13, p < 0.001; conditions F (2,41) = 0.80; interaction F (8,164) = 0.88. From these results it can be concluded that the exercise treatment was effective in reducing subjects’ pre-stress, stress and recovery heart rates relative to subjects who received relaxation training or no treatment.
DISClJSSION
The results of this experiment indicate that a brief aerobic exercise training program was effective for reducing subjects’ heart rate before, during and after moderate psychological stress. It is noteworthy that the exercise treatment reduced the stress heart rate by as much as 17 b.p.m. (a 15% reduction), thus suggesting that the effect may have been clinically significant as well as statistically significant. The magnitude of this reduction is also notable because: (a) it occurred in the context of what was only a moderate stress (remembering numbers and repeating them backwards), (b) it was achieved in healthy subjects who were already in fairly good physical condition (relatively disease-free, active college students with average levels of aerobic fitness). and (c) it was achieved with a relatively brief (29 sessions) intervention program. It may be that greater effects would be achieved in situations involving more stress, populations who are at greater risk, and/or a more intense treatment program. In considering these findings it should be noted that the aerobic exercise training did not reduce the subjects’ response to stress. but instead reduced the subjects’ resting heart rate and that reduction was carried forward to the stress period. The findings revealed an interesting parallel between the effects of the treatment on the cardiovascular responses during physical exercise and psychological stress. The treatment influenced the heart rate response during both exercise and psychological stress but not did not influence the blood pressure response during either exercise or psychological stress. It appears that a different or more intensive approach will have to be taken to influence blood pressure. Finally, the results of this experiment provide a bridge to earlier findings indicating that the more fit persons were less likely to experience health problems and depression following life stress [ 141, that fitness reduced the cardiovascular response to stress among persons with a family history of hypertension such that the fit persons responded like persons who did not have a family history of hypertension [15], that fitness training was related to reductions in depression [16, 171, and that fitness training facilitated cardiovascular and psychosocial recovery of cardiac patients [lS]. It appears that fitness may be a valuable prophylactic for dealing with stress. AcknowlrdRernmfs-Appreciation is due to Nancy Sheldon and Julie Phillips for their assistance with this project. The research was supported in part by a grant from the University of Kansas to David Roth.
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