Preferred Exertion Across Three Common Modes of Exercise Training

Transcription

1 Journal of Strength and Conditioning Research, 2001, 15(4), National Strength & Conditioning Association Preferred Exertion Across Three Common Modes of Exercise Training STEPHEN C. GLASS AND ANGELA M. CHVALA Human Performance Lab, Wayne State College, Wayne, Nebraska ABSTRACT The use of self-selected intensities of exercise may increase adherence to exercise programs by allowing the participant more freedom to choose activities that are enjoyable. However, self-selected intensities may vary across exercise modes, and participants may not choose an intensity that is adequate to produce health benefits. The purpose of this study was to determine influence of exercise mode on self-selected exercise intensities. Eighteen subjects (12 men and 6 women) between the ages of 18 and 25 participated in this study. Preferred intensity tests were performed for 3 modes of exercise (treadmill, cycle ergometer, and stairstepper). V O2 values were obtained continuously and 1-minute averages were recorded at minutes 5, 10, 15, and 20 for each submaximal test. Comparisons were made using a repeated-measures analysis of variance (mode, time, mode time). Scheffe s F test was used to test simple effects. There was a significant increase in the relative V O2 for all 3 modes of exercise across the 20-minute trials (p ). Relative V O2 (%V O2 peak) increased from to 64.71% for cycle exercise, to 63.25% for the treadmill, and to 61.17% for stairstepping. The average relative V O2 for the cycle ergometer ( %) was significantly higher (p 0.02) than both the treadmill ( %) and stairstepper ( %). Relative heart rate (HR) (%HRR) for the stairstepper ( %) and the cycle ergometer ( %) were significantly higher than the treadmill ( %) (P ). There were no significant differences in rating of perceived exertion (RPE) among the 3 modes of exercise. Similar RPE values were reported for the stairstepper ( ), cycle ergometer ( ), and the treadmill ( ). The results indicate that subjects allowed to choose exercise intensity by self-selection chose work rates that were within the moderate range of American College of Sports Medicine guidelines of 50 85% V O2 max for treadmill, cycle ergometer, and stairstepping exercise. Key Words: exercise prescription, stairstepping, RPE, cycle ergometer Reference Data: Glass, S.C., and A.M. Chvala. Preferred exertion across three common modes of exercise training. J. Strength Cond. Res. 15(4): Introduction T here is a wide range of research evidence to support the beneficial effects of physical activity (28). Despite this, no more than 20% of the adult population in the United States engages in optimal levels of activity, defined as having sufficient frequency, intensity, and duration for cardiovascular fitness improvement (27, 28). Even low-intensity activities, when performed on a regular basis, are associated with decreases in cardiovascular morbidity and mortality (19). However, for health benefits to be achieved, physical activity must be continued on a regular basis. Exercise programs should be designed not only to develop optimal fitness, but also to enhance long-term adherence to training. Exercise adherence has been shown to be related to occupational, health, age, race, attitudes, and beliefs (10, 16, 17, 19, 23). Although it has been shown that higher-intensity exercise leads to increased health benefits (1, 22, 24), lower-intensity exercise may improve exercise adherence (6) and thus have more of a long-term health impact. Since 50% of exercise participants drop out within the first 6 months, special attention should be given to participants when initiating their training program (6). The use of self-selected intensities of exercise has been advocated as a means to increase adherence to an exercise program (6, 8, 26). By allowing the participants more freedom to choose activities that they find enjoyable, they may continue to perform exercise on a regular basis. However, there is concern that by allowing self-selection of intensity, participants may not choose an intensity that is adequate to produce health benefits. Dishman et al. showed that both high- and low-fit individuals selected work rates on a cycle ergometer that were around 60% V O2 peak after 20 minutes of exercise (8). Although fitness level may not influence self-selected exercise intensities, participants may choose a different relative intensity because of their familiarity with a given mode (6). Hetzler et al. (15) examined the perceptual responses at fixed blood lactate concentrations between treadmill and cycle ergometer exercise. They found no differences in rating 474

2 Preferred Exertion Across Three Modes 475 Table 1. Subject characteristics. Variable* Mean SD Age (y) Height (cm) Mass (kg) Percent fat RHR (b min 1 ) RSBP (mm Hg) RDBP (mm Hg) * RHR resting heart rate; RSBP resting systolic blood pressure; RDBP resting diastolic blood pressure. of perceived exertion (RPE) at similar blood lactates, suggesting that mode would not influence perception of relative exercise intensity. To date, the effect of mode on self-selected exercise intensity has not been examined. Therefore, the purpose of this study was to determine the preferred intensity of exercise for individuals across 3 common modes of exercise. Methods Subjects Eighteen subjects (12 men and 6 women) between the ages of 18 and 23 years served as subjects for this study. The group was selected on a volunteer basis through personal contact from a college-age population. All of the subjects were free of known cardiovascular disease and other disorders that might have prevented the safe completion of a maximal graded exercise test. Each subject provided written consent and completed a health history questionnaire. Measurement of Subject Characteristics Height and weight of subjects were measured using a Stadiometer (nearest centimeter) and a Health-o-meter scale (nearest 0.01 kg) respectively. Skinfold body density was determined (Lange calipers) using the 3-site Jackson, Pollock equation (22). Body fat was calculated using the Siri equation (25). Resting blood pressure was measured with the subject seated using a standard stethoscope and sphygmomanometer and resting heart rate was measured by manual palpitation of the radial artery. Exercise heart rates were recorded using the Polar Vantage XL heart rate monitor (Creative Health Products, Plymouth, MI). Before all tests, instructions for the Borg s RPE scale were read to all subjects (5). Subject characteristics are presented in Table 1. Study Design Subjects completed a maximal exercise test on both the treadmill and the cycle ergometer. Subjects also performed 3 submaximal tests; one each on the treadmill, cycle ergometer, and the stairstepper. During the submaximal tests, subjects were instructed to choose preferred levels of exertion. The primary consideration in designing the study was that the self-selected exercise intensity should be unbiased and subjective. All tests were administered in a randomized order. Maximal Exercise Tests During the maximal cycle ergometer protocol, subjects warmed up by cycling 2 minutes at 25 or 50 W and 70 rpm. Two-minute stages were used, during which resistance was increased in W increments. During the final 30 seconds of each stage, heart rate (HR), RPE, and oxygen uptake (V O2 ) were recorded. V O2 was recorded using the Quinton Q-plex gas analyzer (Quinton, Bothell, WA). RPE was measured using Borg s 15-point scale of perceived exertion. The test was terminated when subjects indicated that they could no longer continue or when a cadence of 70 rpm could not be maintained. The treadmill maximal test was administered using the standard Bruce protocol. Subjects warmed up by walking 3 minutes at 1.7 mph. Three-minute stages were used in which both speed and grade were increased at approximately 3 maximal exercise test increments. During the last minute of each stage, HR, RPE, and V O2 were recorded. The test was terminated when the subjects indicated that they could no longer continue. Preferred Intensity Trial Preferred intensity tests were performed for 3 modes of exercise (treadmill, Quinton 1860; cycle ergometer, Monark; and stepper, Stairmaster; Quinton, Bothell, WA). Before each test, subjects were read a standard set of instructions (8) that described the procedure used to choose exercise intensity and to ensure that all subjects received the same instructions in choosing that intensity. Each preferred intensity trial was 20 minutes in length. Every 5 minutes subjects were given the opportunity to change the intensity of the exercise bout. For the preferred intensity tests subjects were given a 3-minute warm-up. The warm-up on the treadmill was at 1.7 mph; on the cycle ergometer it was 25 W and 50 W for men and women respectively. The warm-up on the stepper was at the subjects discretion. During the warm-up, subjects were instructed to select the intensity at which they wanted to start. At each 5- minute interval, subjects were given the opportunity to adjust their exercise intensity. During the treadmill exercise bout, subjects indicated changes with hand signals and the researcher adjusted the intensity on the treadmill accordingly. During the cycle ergometer and the stepper exercise bouts, subjects themselves controlled adjustments in work rates. Subjects were not allowed to see the work rate displays. HR and V O2 responses were recorded during each minute of the test and RPE was recorded every 2 minutes.

3 476 Glass and Chvala Table 2. Maximal test data (mean SD). Variable Cycle ergometer treadmill MHR (b min 1 ) V O2 peak (l min 1 ) RER RPE * MHR maximal heart rate; RER respiratory exchange ratio; RPE ratings of perceived exertion. * Significantly different (p 0.05). Results Subject characteristics are presented in Table 1. These subjects represented a healthy, active population of men and women between 18 and 25 years of age. Male subjects were of average to high fitness, with a mean V O2 peak of ml kg 1 min 1 1 and ml kg 1 min for the cycle ergometer and treadmill respectively. Female subjects were of average fitness, with V O2 peak values of ml kg 1 min 1 and ml kg 1 min 1 for the cycle ergometer and treadmill respectively. The mean maximal HR, V O2 peak, respiratory exchange ratio (RER), and RPE for the cycle ergometer and treadmill are reported in Table 2. There was a significant difference in maximal HR between the cycle ergometer and treadmill; however, no significant differences were observed for V O2 peak, RER peak, and RPE peak values. Submaximal Test Data There was a significant increase in the relative V O2 among all 3 modes during the 20-minute exercise bouts (p ). Relative V O2 increased from to 64%, to 63.25%, and to 61.17% V O2 peak across the 20 minutes of exercise for the cycle ergometer, treadmill, and stairstepper respectively. The mean relative V O2 for the cycle ergometer ( ) was significantly higher (p 0.02) than both the treadmill ( ) and stairstepper ( ). Submaximal V O2 data are shown in Figure 1. Relative HR values (%HRR) for the stairstepper ( ) and the cycle ergometer ( ) were significantly higher than the treadmill ( ) (p ). HRR increased significantly across time for all modes of exercise. Submaximal HR data are shown in Figure 2. There were no significant differences in RPE among the 3 modes of exercise. Mean RPE values were around the somewhat hard level for the cycle ergometer treadmill and stairstepper respectively ( vs vs ). There were significant increases in RPE across time. RPE data are shown in Figure 3. Discussion The results of the present study show that subjects allowed to self-select exercise intensity chose work Figure 1. Percent V o 2 peak across time for 3 different modes of exercise. Asterisk (*) indicates cycle ergometer significantly greater than treadmill and stairstepper. Data expressed as mean SD. Figure 2. Percent heart rate max across time for 3 different modes of exercise. Data expressed as mean SD. Asterisk (*) indicates significant difference between treadmill exercise and both cycle ergometry and stairstepping. Figure 3. Mean rating of perceived exertion across time for 3 different modes of exercise. Data expressed as mean SD. rates that were within the American College of Sports Medicine (ACSM) guidelines of 50 85% V O2 max (1). This was apparent across treadmill, stair stepper, and cycle ergometer exercise. The relative intensity chosen for cycle ergometer exercise was significantly higher than both treadmill and stairstepping exercise; however, the cycling intensity was still witin a moderate

4 Preferred Exertion Across Three Modes 477 range. Self-selected work rates have been shown by others to fall within commonly prescribed exercise intensities (8, 26). Spellman et al. (26) assessed self-selected exercise intensities of habitual walkers. Subjects were instructed to perform a typical walking bout while speed was measured by an unseen observer. Subjects repeated the identical velocity walking on a treadmill while metabolic variables were measured. Results indicated that preferred walking speeds were equivalent to an exercise intensity of % V O2 max. Dishman et al. (8) compared responses to preferred intensities of exertion in men differing in activity level. Subjects selected a preferred work rate during 20 minutes of cycle ergometer exercise. Results showed that subjects chose a work rate that averaged % V O2 peak for both high and low fitness level. The subjects in the present study selected similar cycling and treadmill work rates. Our results show that individuals are able to self-select an exercise intensity sufficient to induce cardiovascular conditioning. Our results also show that subjects did not simply select a singular work rate for the entire 20-minute bout, but rather used a type of pacing strategy. Oxygen consumption, HR, and RPE all increased linearly across time for all 3 modes of exercise, indicating that the subjects gradually increased work rate as the bout continued. This gradual increase may have served as a prolonged warm-up strategy. The subjects were given a 5-minute warm-up before each exercise bout. Although this is a typical warm-up, it may not have been sufficient for the subjects to feel comfortable and choose a consistent exercise intensity. Dishman (7) observed a similar response, where the highly active subjects gradually increased their power output throughout the 20 minutes of cycling. In contrast, the low-active subjects maintained a near-constant power output. This type of response suggests that those more accustomed to exercise use a pacing strategy to ensure a more comfortable exercise bout. The subjects in the present study were above average in fitness (Table 2) and demonstrated a pacing response similar to the highly active group of Dishman et al. (8). Although subjects chose an exercise intensity that was within ACSM guidelines for training, subjects chose a significantly higher intensity for cycle exercise than treadmill or stairstepping. Again the results are consistent with previous research, which shows that subjects choose a relative intensity for walking that was close to 50% V O2 peak, whereas for cycle exercise the intensity was around 60% (8, 26). Interestingly, although both treadmill and stairstepping exercise elicited a similar relative V O2, the HR response for stairstepping exercise was significantly greater. This elevated HR response for stairstepping has been shown in previous research (4) and may be the result of differences in joint movement (18, 20). Perception of effort was similar across all 3 modes of exercise. This was true despite the significantly higher relative intensity chosen for cycle ergometer exercise. Mean RPEs for all modes fell between 12 and 13, which corresponds to somewhat hard on the Borg scale. These values also fall within the commonly prescribed RPE intensity by ACSM (1). The consistent relation between RPE and V O2 have been demonstrated in the past; however, the studies generally used either an estimation (3, 4, 14) or a production (10 13) protocol. In the present study the subjects chose a comfortable intensity without receiving any prior pacing. Our results show that the RPEs for the selected work rates were within prescriptive ranges. The higher relative V O2 for cycle ergometer exercise despite no differences in RPE could be attributed to the resolution of the RPE scale for estimating work intensity. An RPE of 12 to 13 represents a relative intensity between 50 and 60% V O2 max (1), which corresponds to the results from the present study. Perception of effort has been shown to provide a valid means of prescribing exercise intensity (1, 3, 10 13). However, for RPE to be used effectively, some type of learning trial is necessary. The advantage of selfselected exercise is that each individual chooses an intensity of training that is most comfortable for him or her. In addition, no learning trial is required, which improves the feasibility of self-selected exercise prescription in an environment where individual attention is not possible. Subjects appear to choose an intensity that is both intense enough to stimulate cardiorespiratory adaptation, and also meet the recommendations for moderate exercise. The recent release of the Surgeon General s report on physical activity suggests daily moderate exercise for at least 30 minutes (28). Instructions for participants to self-select their exercise intensity may help reach a wide range of individuals, while also contributing to enhance exercise adherence. Encouraging exercise participants to choose their preferred mode of exercise as well as a preferred intensity may contribute to the enjoyment of exercise by a wider range of individuals. Research has shown that although high-intensity aerobic exercise more rapidly improves cardiovascular fitness and expends more energy during a 30-minute exercise bout (1, 2, 7), adherence rates to such a program are much lower compared with a moderate exercise program, and high-intensity exercise is not as enjoyable nor as well tolerated by nonathletes training for health and fitness. Thus, the most beneficial type of exercise program for he majority of the population is one that promotes moderate-intensity exercise. Exercise prescription by allowing participants to choose their preferred intensity offers a method of increasing exercise adherence while improving cardiovascular fitness. Self-selection of intensity may also help the participants naturally adjust their work rate to account for improve-

5 478 Glass and Chvala ments in aerobic capacity. Typically, as individuals improve aerobic capacity, they completed a second graded exercise test, followed by a revision of their training program based upon their new V O2 max. For participants who wish to use a variety of modes for exercise, and thus require different HR prescription, exercise testing becomes very time consuming and costly. Using self-selected intensities, individuals should naturally increase their work rate as they improve fitness. In addition, participants will choose intensities on each mode that provide a similar relative training intensity. This may assist the facility that cannot perform repeat testing as often as needed, and puts control of the exercise program in the hands of the participant, requiring less frequent monitoring by the staff. In conclusion, the results of the present study show that self-selected exercise intensity does not differ across treadmill, cycle ergometer, and stairstepping exercise. In addition, the selected intensities fall within ACSM guidelines for improving cardiorespiratory fitness. Exercise prescription using self-selected intensities may improve exercise adherence across a wide range of exercise participants. Practical Applications Designing exercise training programs that ensure adequate cardiovascular conditioning while promoting adherence are essential for individuals seeking to maintain an exercise program. Programs that base exercise intensity on estimated HR ranges, or training intensities that must cross exercise modes, can result in inappropriate training intensities and subsequent failure of the program. The present study provides evidence that individuals seeking to improve their cardiovascular fitness are able to self-select a training intensity that not only feels most comfortable to them, but also falls within a training range that will result in cardiovascular conditioning. In addition, this ability appears to cross exercise modalities, adding to the efficacy of use. The advantages of self selected intensity include: a more appropriate training range, more natural increases in work intensity as the client becomes conditioned, and fewer technological aids required for intensity monitoring. In typical health facilities there is very little monitoring of exercise intensity, yet intensities are calculated for clients and they seek to reach the intensity prescription. Self-selected work intensity appears more meaningful for the client, because it allows them more control over their program, and yet still allows for adequate cardiovascular conditioning. This method of exercise program design should be examined more carefully for an apparently healthy population. Note: Stephen Glass is now with the Department of Movement Science at Grand Valley State University, Allendale, MI References 1. American College of Sports Medicine. Guidelines for Exercise Testing and Prescription (5th ed.). Philadelphia: Williams & Wilkins, BADENHOP, D.T., P.A. CLEARY, S.F. SCHAAL, E.L. FOX, AND R.L. BARTELS. Physiologic adjustments to higher- or lower-intensity exercise in elders. Med. Sci. Sports Exerc. 15: BAYLES, C.M., K.F. METZ, R.J. ROBERTSON, F.L. GOSS, J. COSGRO- VE, AND D. MCBURNG. Perception regulation of prescribed exercise. J. Cardiopulm. Rehabil. 10: BEN-EZRA, V., C. LACY, AND D. MARSHALL. Perceived exertion during graded exercise: Treadmill vs step ergometry. Med. Sci. Sports Exerc. 24:S BORG, G. Perceived exertion as an indicator of somatic stress. Scand. J. Rehabil. Med. 2: CUNNINGHAM, D.A., P.A. RECHNITZER, M.E. PEARCE, AND A.P. DONNER. Determinants of self-selected walking pace across ages 19 to 66. J. Gerontol. 37: DISHMAN, R.K. Exercise Adherence: Its Impact on Public Health. Champaign, IL: Human Kinetics, pp DISHMAN, R.K., R.P. FARQUHAR, AND K.J. CURETON. Responses to preferred intensities of exertion in men differing in activity levels. Med. Sci. Sports Exerc. 26: DISHMAN, R.K., R.W. PATTON, I. SMITH, R. WEINBERG, AND A. JACKSON. Using perceived exertion to prescribe and monitor exercise training heart rate. Int. J. Sports Med. 8: DISHMAN, R.K., AND J. SALLIS. The determinents of physical activity and exercise. Public Health Rep. 100: DUNBAR, C.C., R.J. ROBERTSON, R. BAUN, M.F. BLANDIN, K. METZ, R. BURDETT, AND F.L. GOSS. The validity of regulating exercise intensity by ratings of perceived exertion. Med. Sci. Sports Exerc. 24: ESTON, R.G., B.L. DAVIES, AND J.G. WILLIAMS. Use of perceived effort ratings to control exercise intensity in young healthy adults. Eur. J. Appl. Physiol. 56: GLASS, S.C., R.G. KNOWLTON, AND M.D. BECQUE. Accuracy of RPE from graded exercise to establish exercise training intensity. Med. Sci. Sports Exerc. 24: GUTMAN, M.C., R.W. SQUIRES, M.L. POLLOCK, C.FOSTER, AND J. ANHOLM. Perceived exertion Heart rate relationships during exercise testing and training in cardiac patients. J. Cardiopulm. Rehabil. 1: HETZLER, R.K., R.L. SEIP, S.H. BOUTCHER, E. PIERCE, D. SNEAD, AND A. WELTMAN. Effect of exercise modality on ratings of perceived exertion at various lactate concentrations. Med. Sci. Sports Exerc. 23: KING, A.,S.N.BLAIR, D.BILD, R.K.DISHMAN, P.M.DUBBERT, B. H. MARCUS, N.B.OLDRIDGE, R.S.PAFFENBARGER, K.E. POWELL, AND K. K. YEAGAR Determinants of physical activity and intervention in adults. Med Sci. Sports Exerc. 24(Suppl): S221 S LEE, J.Y., B.E. JENSEN, A. OBERMAN, G.F. FLETCHER, B.J. FLETCH- ER, AND J.M. RACZYNSKI. Adherence in the training levels comparison trial. Med. Sci. Sports Exerc. 28: LOLLGEN, H., T. GRAHAM, AND G. SGOGAARD. Muscle metabolites, force and perceived exertion bicycling at varying pedal rates. Med. Sci. Sports Exerc. 12: MARTIN, J.E., AND P.M. DUBBERT. Adherence to exercise. Exerc. Sport Sci. Rev. 13: PANDOLF, K.B., AND B.J. NOBLE. The effect of pedaling speed and resistance changes on perceived exertion for equivalent power outputs on the bicycle ergometer. Med. Sci. Sports. 5: POLLOCK, M.L., H.S. MILLER, R. JANEWAY, A.C. LINNERUD, B.

6 Preferred Exertion Across Three Modes 479 ROBERTSON, AND R. VALENTINO. Effects of walking on body composition and cardiovascular function of middle-aged men. J. Appl. Physiol. 30: POLLOCK, M.L., D.H. SCHMIDT, AND A.S. JACKSON. Measurement of cardiorespiratory fitness and body composition in the clinical setting. Compr. Ther. 6: SALLIS, J.F., W.L. HASKELL, S.P. FORTMAN, K.M. VRANIZAN, C.B. TAYLOR, AND D.S. SOLOMON. Predictors of adoption and maintenance of physical activity in a community sample. Prev. Med. 15: SIDNEY, K.H., AND R.J. SHEPHARD. Frequency and intensity of exercise training for elderly subjects. Med. Sci. Sports 10: SIRI, W.E. Body composition from fluid spaces and density: Analysis of methods in techniques for measuring body composition. Washington DC: National Academy of Sciences, National Research Council, pp SPELLMAN, C.C., R.R. PATE, C.A. MACERA, AND D.S. WARD. Self-selected exercise intensity of habitual walkers. Med. Sci. Sports Exerc. 25: STEPHENS, T., D.R. JACOBS, AND C.C. WHITE. A descriptive epidemiology of leisure-time physical activity. Public Health Rep. 100: U.S. Department of Health and Human Services. Physical Activity and Health: A Report of the Surgeon General. Atlanta, GA: U.S. Dept. of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996.