Perceptual and Motor Skzlls, 2007, 104, 1079-1087. 0Perceptual and Motor Skills 2007
RATINGS OF PERCEIVED EXERTION DURING INTERMITTENT AND CONTINUOUS EXERCISE ' ALAN C. UTTEK, DAVID C. NIEMAN, CHARLES L. DUMKE, STEVEN R. McANULTY
Department of Health, Leisure, and Exercire Science Appalachtan State University JIE KANG
LISA S. McANULTY
Department of Health and Exerci.se Science The College of New lersey, Ewing
Department of Family and Consumer Sciences Appalachian State Uuiver.sity
Summa?.-This investigation characterized the acute differentiated and undifferentiated perceptual responses to a prolonged intermittent and continuous stationary cycle exercise session. Throughout two 2.0-hr. test sessions, 12 subjects cycled at 64% Watts,,, and 73% V 0 2 peak continuously or with 3-min. rest intervals interspersed every 10 min. During both trials, oxygen uptake (VOz), ventilation (VE), respiratory rate, respiratory exchange ratio, heart rate, and three ratings of perceived exertion (OMNI) measurements were made every 30 min. During the intermittent protocol, the perceived exertion measures were taken during Min. 10 of every 10-min. interval. OMNI RPE-Overall body did not differ significantly between conditions. No significant differences were reported for OMNI WE-Legs between conditions; however, a significant interaction was reported for OMNI WE-Chest, which was significantly lower in the continuous condition at Min. 120. These data indicate that perception of exertion is similar during prolonged intermittent and continuous exercise when performed at the same relative intensities throughout 90 min. of exercise.
Metabolic and perceptual responses during intermittent exercise have received increased attention within recent years. An earlier study by Astrand, Astrand, Christensen, and Hedman (1960) found lower oxygen uptake ( V 0 2 ) , heart rate, and blood lactate concentration in intermittent than in continuous exercise performed at the same average intensity by young individuals. Recently, Morris, Gass, Thompson, and Conforti (2003) found attenuated physiological responses following intermittent exercise at 50% and 70% V 0 2 peak for older men. In these studies, the total amount of work completed was kept the same for both exercise conditions. Despite these attenuated physiological responses, Morris, Gass, Thompson, Bennett, Basic, and Morton (2002) reported similar physiological adaptations manifested in improved peak V 0 2 , stroke volume, and cardiac output following 10 'Please address correspondence to Alan C. Utter, Department of Health, Leisure, and Exercise Science, Appalachian State University, Boone, NC 28608 or e-mail (
[email protected]). This work was funded b y The Gatorade Sports Science Institute, Quaker Oats Company, 617 West Main Street, Barrington, IL 60010. DO1 10.2466/l'MS.104.4.1079-1087
A.C. UTTER, ET AL.
wk. of intermittent exercise when compared with continuous training. Again, the total work accomplished was kept the same, so the rest periods and therefore exercise duration differed between the two training regimens. Taken together, these findings suggest that intermittent exercise should be considered an effective alternative training method, especially for those who cannot tolerate exercise for sustained periods of time, such as older or deconditioned individuals. The issue of whether intermittent exercise would be perceived less effortful has not been examined thoroughly in the literature on perceived exertion. Given the interspersed rest periods and potential reduction in VOz and heart rate during intermittent exercise shown in previous research, one may speculate that ratings of perceived exertion would be lower during intermittent than continuous exercise. Early on, Edwards, Melcher, Hesser, Wigertz, and Ekerlund (1972) observed greater perceived exertion during intermittent than continuous exercise which yielded the same total work. They also reported a higher V 0 2 and heart rate associated with the intermittent exercise. The attenuated or augmented physiological responses which were based on exercise protocols were kept similar by having subjects achieve the same percentage of peak power output or accomplish the same amount of external work. This raises the question whether perceived exertion necessarily mirrors the physiological differences between intermittent and continuous exercise. A rival hypothesis is that perceived exertion is simply driven by the overall dose of exercise independent of how an exercise regimen is conducted, i.e., continuous versus intermittent. Kang, Chaloupka, Mastrangelo, Hoffman, Ratamess, and O'Conner (2005) recently examined perceptual responses during Spinning (variable-intensity cycling exercise accomplished by changing workloads during different stages of a workout to reach a different target heart rate throughout the exer. indicated that, when the two exercise protocols were cise ~ e r i o d )Analysis performed at the same percentage of maximal heart rate, perceived exertion remained similar in spite of the changing exercise intensity. It must be emphasized that the Spinning protocol is regarded by fitness processionals and exercise scientists as a variable intensity exercise which differs from an intermittent protocol (Kang, et dl., 2005). In the Spinning protocol, there are no rest periods, and intensity fluctuates in a predetermined order. The present investigation compared acute differentiated and undifferentiated perceptual responses using OMNI RPE in sessions of prolonged intermittent and continuous exercise on a stationary cycle. Unlike most previous studies (Astrand, et al., 1960; Edwards, et al., 1972; Morris, et al., 2003), here an intermittent exercise protocol was used. This consisted of comparatively longer exercise intervals and thus longer total exercise duration. In addition, for both exercise protocols, i.e., continuous versus inter-
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mittent, subjects exercised at the same percentage of V 0 2 peak and peak power output. Through the implementation of this experimental design, one can examine the effect of an exercise protocol in which exercise was interspersed with multiple rest intervals on ratings of perceived exertion.
Subjects Twelve trained male cyclists were recruited as experimental subjects through local and collegiate cycling clubs. Informed consent was obtained from each person, and the experimental procedures were in accord with the policy statements of the institutional review board of Appalachian State University. Reseavch Design This investigation used a perceptual estimation paradigm administered during two 2.0-hr. cycling sessions in counterbalanced order. Subjects cycled for 2.0 hr. at 64% Watts,,, and 73% V 0 2 peak continuously or with 3-min. rest intervals interspersed every 10 min. (2.6 hr. total exercise time including rest intervals). Two to three weeks prior to the first test session, subjects reported to the ASU Human Performance Laboratory for orientation and measurement of body composition and cardiorespiratory fitness. Body composition was assessed by hydrostatic weighing using an electronic load cell system (Exertech, Dresbach, MN), estimated residual volume, and the Siri equation (Siri, 1961). V 0 2 peak was measured using a graded maximal protocol (25-Watt increase every 2 min. starting at 150 Watts), with subjects using their own bicycles on CompuTrainerTMPro Model 8001 trainers (RacerMate, Seattle, WA). Oxygen uptake and ventilation were measured using the MedGraphics CPX metabolic system (MedGraphics Corporation, St. Paul, MN). Heart rate was measured using a chest heart-rate monitor (Polar Electro, Inc., Woodbury, NY). During maximal testing, three separate ratings of perceived exertion were recorded using the adult OMNI-Cycle Scale. This familiarized the subject with the category-scale procedure and established the low and high rating anchors (Robertson, Goss, Dube, Rutkowski, Dupain, Brennan, & Andreacci, 2004). A differentiated rating was assessed for localized feelings of exertion in the legs ( W E in Legs) and for feelings of respiratory exertion in the chest ( W E in Chest). The undifferentiated W E for the overall body ( W E in Overall) was also assessed using this scale. The order of measurements of the three ratings was based on a counterbalanced design. The initial exercise anchoring procedure, presented during the graded exercise test with memory reinforcement of the anchor points, was presented prior to each of the 2.0-hr. cycling sessions. Perceived exertion was defined as the
A. C. UTTER, ET AL.
subjective intensity of effort, strain, discomfort, or fatigue felt during exercise (Noble & Robertson, 1996). The instructional set for the Omni-Cycle Scale and a list of validation studies has been published previously (Robertson, 2004; Robertson, et al., 2004). During orientation, a dietitian instructed the subjects to follow a moderate carbohydrate diet during the three days prior to the cycle sessions and record intake on a food record. The food-intake diaries were analyzed using a computerized dietary assessment program (Food Processor, ESHA Research, Salem, OR).
Cycle Sessions For two 2.0-hr. test sessions subjects cycled at 64% Watts,,, and 73% V 0 2 peak continuously or with 3-min. rest intervals interspersed every 10 min. During the rest intervals subjects remained on their bikes in a stationary position. Subjects self-selected a constant pedaling frequency between 80 and 100 rpm and a constant resistance (64% Watts,,,) to elicit the target of 73% V 0 2 peak for both trials. O n test session dates, subjects reported to the lab at 3:00 pm not having ingested energy in any form after 10:00 am. During the test sessions, experimental subjects cycled using their own bicycles on CompuTrainerTMPro Model 8001 trainers (RacerMate, Seattle, WA). During both trials, oxygen uptake ( V 0 2 ) ,ventilation (VE), respiratory rate, respiratory exchange ratio, heart rate, and measurements of perceived exertion were made every 30 min. during the trials (using the same equipment as at baseline testing). During the intermittent protocol, measures of perceived exertion were taken during the last min. of every 10-min. interval.
Statistical Analysis Values were expressed as means and standard error. Performance measures for the cyclists were compared under the continuous and intermittent conditions, using paired t tests. Perceived exertion measures were analyzed using a 2 (continuous and intermittent conditions) x 4 (times of measurement) repeated-measures analysis of variance. Significant main effects were evaluated with paired t tests using a Bonferroni adjustment, with statistical significance set at p < .02. RESULTS Subjects' characteristics and values from the maximal cardiorespiratory tests for the 12 male cyclists are listed in Table 1. Three-day food records indicated no significant differences in macronutrient intake between test sessions, with mean energy intakes ranging between 12.0 f 0.8 to 13.3 f 0.8 MJ . day-' (2,860 _+ 187 to 3,180 _+ 189 kcal . day1), and percent of energy intakes of 63.0 _+ 1.9 to 60.8 _+ 2.95 % carbohydrate, 26.5 1.8 to 28.1 _+ 1.2% fat, and 14.0 f 1.1 to 14.4 f 0.8% protein.
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INTERMITTENT VS CONTINUOUS EXERCISE: EXERTION TABLE 1 SUBJECTS' CHARACTERISTICS FOR MALECYCLISTS ( N =12) -
Age, yr. Stature, m Body mass, kg Body composition, '% fat Heart rate, maximal, beats . min.-' Powermax, Watts V 0 2 peak, ml . kg-' . min.-' Minute ventilation, maximal, 1 . min.-' Maximal O M N I RPE-Overall, 0-10 Maximal O M N I HIE-Legs, 0-10 Maximal O M N I RPE-Chest, 0-10 ~.~
- . ~
M
SE
21.0 1.8 71.6 11.9 191.0 335 56.9 166 9.1 9.3 8.8
1.0 0.1 1.9 1.0 2 8 1.?J 6 0.2 0.2 0.2
Variable
~- -
Power output and heart rate did not differ significantly between the two experimental conditions and averaged 214 f 5 Watts (63.9f 0.7% Watts,,,), 158 f 3 heart beats/min. (82.6 f 0.9% HR,,,), and 73.1 f 1.5% V 0 2 peak (Table 2). Average OMNI WE-Overall body was not significantly different between the continuous (5.7 f 0.3) and intermittent (5.3 +- 0.3) conditions, respectively. TABLE 2
Medsure
Continuous Condlt~on Interm~ttentCondlt~on -
M
SE
M
SE
V 0 2 , ml . k g ' . min:' XI V 0 2 peak Heart rate, beats . min.-' % FIR,,,
Workload, Watts Watts,,,, Ventilation, 1 . min.-' Respiratory Rate, breaths . min.-' Respiratory exchange ratio, ending End O M N I RPE-Overall Average OMNI KPE-Overall --
--
~p
OMNI W E in Overall body increased over time (F, ,,=41.6, p < .001) for all subjects combined (Table 3). No significant difference was found for OMNI RPE-Overall body between the continuous and intermittent conditions and the interaction (F, ,,= 1.98, p = .14). Similar findings were found for OMNI RPE in Legs, which increased over time (F, ,,=40.6, p < .001), but no significant differences were reported between the conditions or for the interaction (F, ,,= 0.53, p = .67) (Table 3). OMNI RPE in Chest increased
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over time (F, ,,= 33.4, p < .001) for all subjects combined (Table 3). In addition, the interaction was significantly different for OMNI RPE in Chest between the continuous and intermittent conditions (F, ,,= 3.74, p < .05). Post hoc analysis of the interaction indicated that OMNI W E in Chest was lower ( p < .02) in the continuous than in the intermittent condition at 120 min. TABLE 3 MEANS STANDARD ERRORS FOROMNI RPE-OVERALL,-LEGS, AND -CHEST OVERTIME BY EXERCISE CONDITION
+
. .-
Condition
30 min.
M
SE
60 min.
M
SE
90 min. SE
M
-
120 min. SE
M
OMNI-Overall Continuous 4.3 5.4 0.2 0.5 6.3 0.3 6.9 0.3 Intermittent 3.5 0.3 6.2 0.4 7.1 0.5 0.3 4.5 OMNI-Legs Continuous 4.9 0.3 6.0 0.5 7.1 7.8 0.3 0.4 Intermittent 4.4 0.3 5.3 0.3 6.8 0.4 7.9 0.6 OMNI-Chest 3.2 Continuous 4.3 0.5 4.5 0.2 0.4 5.0 0.4 Intermittent 3.2 0.4 5.1 0.5 5.9 3.9 0.3 0.5" "Significant difference in change in continuous and intermittent conditions at 120 min. for OMNI WE-Chest, p < .02.
DISCUSSION Intermittent exercise has unique advantages in that it may be more tolerable given multiple rest periods, while also it produces physiological adaptations similar to continuous exercise. From a metabolic standpoint, having multiple rest-to-exercise transitions is considered beneficial because this can create greater disturbance to the body's homeostasis and subsequently greater energy expenditure during recovery following exercise (Almuzaini, Potteiger, & Green, 1998). This study assessed how this strenuous exercise protocol would be perceived subjectively in comparison with continuous exercise for both physiological and perceptual responses while the average intensity was the same between the two exercise conditions. The primary findings were that perceived exertion assessed by the adult OMNI-Cycle Scale for the legs and the overall body remained similar throughout exercise between the two conditions. OMNI W E for the chest was also similar between protocols throughout most of the 2-hr. session, but it became significantly higher at the end of exercise during the intermittent than the continuous condition. The fact that perceived exertion for the legs and the overall body were not significantly different was expected. As may be seen in Table 2, the physiological mediators known to affect the perception of exertion such as V 0 2 and heart rate
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were similar between the two exercise conditions. Perceived exertion for the chest represents primarily the ventilatory drive or upper body muscular exertion. An increase in this variable suggests that subjects perceptually felt their breathing as comparatively heavier or felt an increase in upper body muscular effort during the later stages of intermittent exercise. It is thought that this measure is influenced ~rimarilyby ventilatory drive, which can be evaluated via measuring ventilation or respiratory rate (Robertson, 1982). However, these two parameters did not differ between the two exercise conditions in the present investigation, which raises the question of what other factors may have mediated the increase in this measure of differentiated perceived exertion. Following the rest periods in the intermittent condition, these cyclists were required to increase their power output from zero to their prescribed submax power output (214 f 5 Watts). This task was often accomplished by the cyclists getting up off the seat, firmly gripping the handlebars, and recruiting upper body musculature to accelerate the pedals against the greater load. In the intermittent condition, the cyclists were required to complete this activation activity 11 times throughout the 2.0-hr. trial. During the continuous condition, the cyclists did not need to accelerate from O to over 200 Watts multiple times, therefore, less upper body musculature recruitment was initiated. This observation may partially explain why OMNI RPE-Chest was significantly higher at the end of the intermittent exercise session, although further evidence for this contention is needed. Present results suggest that as long as the average intensity remains similar, the perception of exertion during intermittent exercise is not different from that during continuous exercise despite the multiple rest periods. Given the potential physiological advantages associated with intermittent exercise, the finding that perceived exertion for the legs and the overall body did not differ between the two conditions can be viewed as evidence supporting use of this exercise protocol as an alternative exercise training method. Therefore, as discussed earlier, intermittent exercise may be more tolerable, augment expenditure of postexercise energy, yet also produce similar physiological adaptation when compared with continuous exercise. These advantageous responses, however, are achieved with the same amount of perceived exertion. In the present study, the total time of the intermittent exercise session was longer, i.e., 2.6 vs 2.0 hr. given the inclusion of the 3-min. rest periods. Researchers should investigate how perceived exertion might change were the duration of the entire workout sessions kept the same. In this example, more intense exercise intervals of shorter duration would have to be included in the exercise session to allow rest intervals to be included, thereby expanding the total workout time. It is also possible that the cumulative effect of the repeated exercise bouts which were higher on OMNI
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RPE-Chest at the end of exercise reflect the longer intermittent exercise session. In the present study, there were no significant differences in V 0 2 , ventilation, and heart rate between the intermittent and continuous exercise conditions. This finding is not consistent with early studies in which significantly lower physiological responses were found during an intermittent exercise protocol (Wstrand, et al., 1960; Morris, et al., 2003). It must be noted that in the previous studies, the exercise intervals lasted only 60 sec., whereas in the present study an exercise interval of 10 min. was employed. At the onset of exercise, there is always a lag in oxygen consumption, which occurs because the cardiopulmonary system requires time to become fully activated to meet the increased demands (Powers & Howley, 2001). In this context, it is conceivable that V 0 2 and heart rate measured during an exercise interval of shorter duration would be affected more by such a functional delay in participants' responses in comparison with values of an exercise interval of longer duration. Using a variable intensity protocol in which subjects exercised at lower intensities sporadically instead of resting, Palmer, Borghouts, Noakes, and Hawley (1999) also reported no differences in V 0 2 , ventilation, heart rate, and rated perceived exertion between variable intensity and constant-load exercise of prolonged duration ( > 2 hr.). These authors suggested that, when the duration of a workload was short (
