WORK DISTRIBUTION INFLUENCES SESSION RATINGS OF PERCEIVED EXERTION RESPONSE DURING RESISTANCE EXERCISE MATCHED FOR TOTAL VOLUME JUSTIN A. KRAFT,1 JAMES M. GREEN,2 1 2
AND
TYLER M. GAST1
Department of Health, Physical Education and Recreation, Missouri Western State University, St Joseph, Missouri; and Department of Health, Physical Education and Recreation, University of North Alabama, Florence, Alabama
ABSTRACT Kraft, JA, Green, JM, and Gast, TM. Work distribution influences session ratings of perceived exertion response during resistance exercise matched for total volume. J Strength Cond Res 28(7): 2042–2046, 2014—Session ratings of perceived exertion (SRPE) are sensitive to changes in total work volume and work rate during resistance training. This study examined the influence of work distribution (varied load, set, and repetitions [reps]) on SRPE in 2 resistance exercise trials matched for total work volume (sets 3 reps 3 percentage of 1 repetition maximum [% 1RM]) and work rate (total work volume/time). Participants completed a low load/high rep (LLHR) trial (2 sets 3 12 reps 3 3-minute recovery at ;60% 1RM) and a high load/low rep (HLLR) trial (3 sets 3 6 reps 3 1.5-minute recovery at ;80% 1RM) of the bench press, lat pull-down, overhead press, upright row, triceps extension, and biceps curl. A 2-minute recovery separated each exercise in both trials. Session ratings of perceived exertion and recovery heart rate (HR) were recorded 20 minutes after exercise. Preset and postset RPE and HR were higher for HLLR vs. LLHR (3.1 6 1.6; 104 6 15 b$min21 vs. 2.1 6 1.3; 98 6 10 b$min21) and (5.5 6 0.9; 139 6 14 b$min21 vs. 4.4 6 0.9; 131 6 12 b$min21), respectively. Session RPE was higher for HLLR (5.7 6 1.4) vs. LLHR (4.3 6 1.4) with no difference in recovery HR. Session ratings of perceived exertion was greater with higher load despite matched total volumes and work rates. Higher preset acute RPE and HR in HLLR may indicate differences in recovery between sets. Higher postset acute RPE and HR in HLLR indicated increased difficulty of individual sets in HLLR, which likely contributed to SRPE differences. Practitioners can be confident that SRPE accurately reflects changes in training load
Address correspondence to Justin A. Kraft, [email protected]. 28(7)/2042–2046 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
2042
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when the number of sets, reps, and loads are altered within routine training.
KEY WORDS RPE, strength training, training load INTRODUCTION
T
he session ratings of perceived exertion (SRPE) is a subjective measure of global training load. It is postulated that the SRPE represents as “gestalt” experience, which incorporates a variety of physiological and perceptual cues into a single global marker of exercise intensity (2,21). As such, the SRPE has been shown to be a versatile measure capable of validly assessing exercise intensity in exercise paradigms that are intermittent in nature including resistance exercise (4,7,10,12,18–21,24,27). Although SRPE has been validated in numerous settings, relatively little is known about the precise factors that contribute to the gestalt experience reflected in SRPE. Session RPE may be influenced by a number of metabolic and physiologic factors (metabolic acidosis, etc.), which may vary as exercise parameters such as intensity, repetitions (reps), and recovery period are changed (27). Early research indicated that intensity (as measured by percentage of 1 repetition maximum [1RM]) was a key mediating factor and that SRPE increased with increases in the percentage of 1RM lifted (4,18,27). However, Pritchett et al. (22) reported higher SRPE at lower relative resistance (% 1RM) during resistance training to failure, noting that participants performed more total volume of work at lower intensities. This led authors to conclude that total volume lifted was a principle mediating factor. More recent work has examined the influence of work rate (total volume lifted per unit time) on SRPE response during resistance training by comparing 3 resistance exercise protocols: (a) 3 sets 3 8 reps 3 60% 1RM 3 1.5-minute recovery between sets, (b) 2 sets 3 12 reps 3 60% 1RM 3 3-minute recovery between sets, and (c) 3 sets 3 8 reps 3 60% 1RM 3 3-minute recovery between sets. Results indicated that SRPE was linked more closely to changes in work rate than to the number of sets and reps per set (13). Additionally, authors noted a trend (p = 0.08) toward increased
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Journal of Strength and Conditioning Research SRPE when performing higher reps and fewer sets despite lifting equal volumes. Authors also noted higher postset acute RPE in this condition (likely resulting from completing more total work per set) and postulated that the difficulty of individual sets may serve as a mediating factor influencing SRPE and warrants further investigation (13). One limitation was that load was held constant in the study at 60% of 1RM in all protocols. Therefore, the purpose of this study was to examine the influence of the independent variable work distribution (varied load, set, and reps) on the dependent variable SRPE during 2 resistance exercise trials matched for total work volume and work rate.
METHODS Experimental Approach to the Problem
A within-subjects repeated-measures design was used to examine the influence of the independent variable (work distribution) on the dependent variable SRPE during 2 resistance training protocols matched for total volume and work rate (total volume/unit time) across the entire bout. Work distribution was manipulated by varying reps, sets, and resistance as a unit. These 3 variables are often altered concurrently in natural settings (i.e., increases in load naturally prompt a reduction in reps), yet the influence on perceptual responses is not well understood. Participants completed an initial session that included the determination of a 1RM for the bench press, lat pull-down, overhead press, upright row, triceps press down, and barbell curl. Participants additionally completed 2 experimental trials consisting of performing the aforementioned exercises according to following protocols: (a) low load/high rep (LLHR) 2 sets 3 12 reps 3 3-minute rest at ;60% of 1RM and (b) high load/low rep (HLLR) 3 sets 3 6 reps 3 1.5-minute rest at ;80% of 1RM. Exercises were performed in the order listed and trials were counterbalanced. One warm-up set of 12 reps with ;40% of the predetermined 1RM was performed before the bench press. This was followed by a 2-minute recovery period. No warm-up was performed before other exercises. A standard 2-minute rest period was provided between all exercises in both trials. These 2 protocols were designed to equate workloads (offset the decrease in reps 3 set 3 6 reps = 18 reps vs. 2 set 3 12 reps = 24 reps with a proportional increase in intensity [80 vs. 60% 1RM]). Additionally, recovery periods between sets were designed to equate total recovery time across the entire exercise bout. Therefore, both total exercise trial duration and duration of each exercise within the trial were constant (i.e., 2 sets 3 12 reps 3 60% 1RM with 3-minute rest required an equivalent time as 3 sets 3 6 reps 3 80% 1RM with 1.5-minute rest). In this way, work completed per unit time (i.e., work rate) was controlled between trials. As such, work distribution was isolated as the independent variable. The selection of the 60 and 80% intensity levels was based on the rep to load relationship set forth by the National Strength and Conditioning Association (1) and selected to ensure that
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participants could complete all reps in both trials, which was necessary for matching total volume. Subjects
Fourteen recreationally strength-trained (strength training $ 2 times per week for a minimum of 6 weeks) male volunteers between the ages of 18 and 25 years (age, 20.8 6 1.7 years; height, 180 6 5 cm; weight, 81.9 6 13.3 kg; percent body fat, 11.6 6 4.9%) were recruited. A prerequisite of 6 uninterrupted weeks of training before study inclusion ensured a minimal level of resistance training experience and ensured that differences in RPE would not result from changes in strength attributable to our exercise protocol. All participants received a clear explanation of the study and signed a written informed consent before participation. Procedures were approved a priori by the local institutional review board for the protection of human subjects. All participants were screened before the study for physical problems contraindicating physical activity (Physical Activity Readiness Questionnaire [PAR-Q]) (28). All subjects were nonsmokers. Participants were instructed to continue with their normal diet (including dietary vitamins/supplements) through the duration of the study to decrease likelihood of confounding potential of nutritional changes during participation. Participants were instructed to report for testing in a well-hydrated state, 1.5–3 hours after their last meal, to refrain from resistance exercise on the day prior (;24–48 hours) and all strenuous physical activity ;24 hours before testing and to avoid caffeine on the day of testing. Procedures
Participants reported for testing on 3 occasions. During the first trial, they completed a health questionnaire and informed consent and were measured for descriptive data (age [years], height [cm], weight [kg], and percent body fat using an Omron body fat analyzer, Omron Healthcare Inc., Bannockburn, IL, USA). A 1RM was then determined for each of the 6 exercises performed in experimental trials. Participants then returned on separate days and completed the 2 counterbalanced resistance training protocols: (a) LLHR 2 sets 3 12 reps 3 3-minute rest at ;60% of 1RM and (b) HLLR 3 sets 3 6 reps 3 1.5-minute rest at ;80% of 1RM. During experimental trials, heart rate (HR) via polar HR monitor (Polar Inc., Port Washington, NY) and acute ratings of perceived exertion (RPE) were measured before (preset) and after (postset) each set. Session RPE (global exercise RPE) and recovery HR were recorded 20 minutes after bout completion. All perceived exertion ratings were estimated according to the 10-point omni scale for resistance training (23). This scale is comprised of a visual scale with verbal anchors for estimating feelings of exertion. Preset RPE was a measure of perceived vigor (no actual exertion at moment recorded) and was measured by having participants respond to the question “How do you feel?” The preset RPE was designed to assess subjective feelings of “preparedness” or “acute recovery.” The RPE scale was used for this measure VOLUME 28 | NUMBER 7 | JULY 2014 |
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Work Distribution Influences SRPE thereby avoiding additional rating scales, which may have introduced confusion for participants. Preset RPE has previously been used to assess recovery while investigating the influence of 3 different rest intervals during a multiset squat routine (15). Session RPE was estimated by asking participants the question, “How was your workout?” (6). This variable provides a subjective estimate of the global difficulty of the entire exercise bout.
RESULTS
One Repetition Maximum Determination
DISCUSSION
Exercises were performed in the following order: bench press, lat pull-down, overhead press, upright row, triceps press down, and barbell curl. The 1RM was defined as the heaviest weight the participant was able to lift for 1 complete repetition (24). Determination of the 1RM was performed according to the procedure outlined by Baechle and Earle (1). Participants performed a light warm-up with a resistance they estimated they could lift 5–10 times. After a 1-minute rest, the participant performed a second warm-up using a weight they estimated they could lift 3–5 times. Twominute rest was provided. At this time, the participant estimated a near maximal load (one they expected to perform 2 or 3 times) and performed the final warm-up followed by 3-minute rest. The load was increased to an estimated maximum (add 10–20 lbs for upper body) and a 1RM was attempted. If successful, 3-minute rest was provided and an additional attempt was made with a new estimated weight. If unsuccessful, 3-minute rest was provided and another attempt was made with a reduced load. Loads were adjusted based on participant feedback with the goal of identifying the 1RM within 3–5 attempts. A 3-minute rest was allowed between exercises.
Preset and postset RPE and HR values are listed in Table 1. Preset and postset RPE and HR averaged across the exercise trials were significantly higher for HLLR vs. LLHR. Session RPE was significantly higher for HLLR (5.7 6 1.4) vs. LLHR (4.3 6 1.4) with no difference in recovery HR (HLLR: 88 6 17 b$min21 vs. LLHR: 89 6 10 b$min21).
Session RPE increased with higher load despite matched total volumes and work rates. This indicates that intensity may be a primary mediating factor responsible for SRPE estimations and corresponds with previous findings that reported higher SRPE as resistance (as a %1RM) increased (4,18,27). However, it should be noted that total volume lifted was equated between trials as previous research has shown that differences in total volume of weight lifted may overshadow intensity in determining SRPE (22). An alternative explanation is that the difficulty of individual sets within a resistance exercise bout may partially mediate SRPE responses. Higher postset HR was observed in HLLR vs. LLHR, which indicated greater physiological strain during individual sets in HLLR. The increased strain was reflected in higher postset RPE in HLLR. Thus, participants also perceived individual sets as more difficult in HLLR than LLHR. The increased difficulty of individual sets in HLLR likely contributed to SRPE differences and indicates that the difficulty of individual sets within a resistance exercise bout contributes to the overall estimation of difficulty reflected in SRPE. Perceptual measures represent a culmination of input from multiple sources. As such, Statistical Analyses current results do not indicate that difficulty experienced in A 6 exercise 3 2 protocol repeated-measures analysis of an individual set is the only or even the dominant mediator variance was used to detect difference among trials for for SRPE. However, responses do suggest a link. These preset RPE, postset RPE, preset HR, postset HR (averaged findings coincide with previous work from our laboratory across trials). Bonferroni follow-up tests (16) were used to showing a trend toward higher SRPE after completing 2 sets assess pairwise comparisons (set by set). A paired t-test was 3 12 reps 3 60% 1RM vs. 3 sets 3 8 reps 3 60% 1RM of the used to determine differences in SRPE and recovery HR. same 6 exercises (13). In this study, higher postset RPE was Differences were considered significant at the p # 0.05 level associated with the protocol containing a greater number of (2-tailed test). sets and lower reps per set, whereas in Kraft et al. (13) greater postset RPE occurred during the protocol containing fewer sets but higher reps per TABLE 1. Pre- and postset average acute ratings of perceived exertion and heart set. In other words, increases in rate by exercise protocol.* SRPE seem to be associated Preset HR Postset HR with higher postset RPE. Condition Preset RPE Postset RPE (b$min21) (b$min21) Combining these 2 results would indicate that the strain LLHR 2.1 6 1.3 4.4 6 0.9 98 6 10 131 6 12 (as reflected in postset RPE) HLLR 3.1 6 1.6† 5.5 6 0.9† 104 6 15† 139 6 14† within the individual sets has *RPE = ratings of perceived exertion; HR = heart rate; LLHR = low load/high rep; HLLR = a stronger link with SRPE than high load/low rep. reps per set or number of sets. †LLHR vs. HLLR (p # 0.05). It is also plausible that greater strain resulted in concomitant
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Journal of Strength and Conditioning Research changes in physiological variables (i.e., pH) potentially linked with elevations in SRPE. However, in this study, direct evidence supporting this notion is lacking. This interpretation may also help explain the influence of load on SRPE as both acute RPE (4,9,14,26,27) and SRPE (4,18,27) have been reported to increase as intensity (%1RM lifted) increases. It should be noted that resistance exercise in the current paradigm included a fixed end point. It has been postulated that during resistance exercise with fixed termination criteria, load (%1RM) may play a more critical role as participants will likely focus on the heaviness of the lift rather than actual exertion when estimating RPE (13,22). Pritchett et al. (22) reported higher acute RPE and SRPE during light intensity (60% 1RM) vs. high intensity (90% 1RM) resistance exercise to failure and attributed this to the completion of a greater volume of work completed in each exercise in the lower intensity trial. In this study, higher postset RPE was associated with the HLLR trial despite completing less work per set in this trial. Even so, higher SRPE did correspond with higher postset RPE in both studies and corroborates previous research, which concluded that average RPE and SRPE are complimentary measures (4). Still, interpreting the influence of postset RPE on SRPE should be done with caution as previous research has noted that average acute RPE and SRPE are not identical measures and that SRPE seems to provide different (17,24) (or perhaps additional) information. Previous resistance training research has indicated differences in salivary cortisol response during low intensity (30% 1RM) and high intensity (75% 1RM) exercise (18) and has also shown that altering the number of sets influences hormonal response to resistance exercise (25). Research comparing matched volumes of interval cycling to constant load cycling noted higher levels of blood lactate during interval exercise, which corresponded to higher SRPE after interval cycling (10). A similar mechanism may apply to the current findings as higher postset RPE in HLLR may also indicate a greater metabolic disruption within the HLLR exercise protocol thus contributing to the difference in SRPE, although this is speculative and was not measured in this study. Higher postset HR similarly attests to greater physiological demands in HLLR. Preset HR and RPE were significantly affected by set distribution, resistance, and recovery period. Ratings of perceived exertion (measured after the first rep of a set) has been shown to increase with shorter rest intervals leading authors to conclude that RPE can be considered a valid measure of muscle recovery (5). Other studies have assessed recovery through the estimation of preset RPE (13,15). For example, Larson and Potteiger (15) used preset RPE to examine the influence of 3 different recovery periods during a multiset squat (reps to failure) resistance protocol and concluded that similar preset RPE values despite different recovery parameters indicated similar recovery between conditions. In contrast, higher preset RPE and HR in HLLR indicated
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reduced recovery between sets vs. LLHR in this study. Differences in recovery between sets may have been attributable to differing metabolic disruption in the HLLR protocol indicated by higher postset RPE as postulated above. Thus, the shorter recovery period between sets in HLLR likely inhibited participants’ ability to recover as effectively (vs. LLHR) for similar performance in subsequent efforts. Differences in SRPE despite no difference in recovery HR indicate that SRPE is sensitive to variation in work distribution but is estimated independently of recovery HR. When originally developed, it was suggested that SRPE be estimated 30 minutes after exercise to prevent terminal exercise conditions from influencing the estimation (4,7,8,27). It has since been shown that RPE at exercise endpoint does not influence SRPE (11) and that SRPE estimations recorded 15 minutes or greater after exercise termination do not differ (13,24).
PRACTICAL APPLICATIONS The ability to quantify exercise load significantly influences the development and implementation of strategies designed to maximize training-induced benefits (3,29). However, traditional measures of training load, such as HR, are inadequate during intermittent activity comprised high intensity bouts with recovery periods interspersed such as resistance training (7). Additionally, these methods often present a practical barrier in the form of the time and equipment required for monitoring. As such, a valid alternative method that can quantify training load in a single marker is of great practical benefit to coaches and practitioners (7,8). The SRPE provides this alternative measure. This study expands the understanding of the factors that mediate SRPE responses. Results indicate that load is a primary mediating factor during resistance exercise to fixed termination criteria (i.e., number of sets and reps). It further confirms that postset RPE measurements compliment the SRPE (4). Therefore, both acute postset RPE and SRPE provide a viable alternative to objective markers of intensity during resistance exercise. The SRPE appears to be a highly sensitive marker, which responds to a variety of training parameters which are often manipulated during the course of training. Practitioners can thus be confident that SRPE provides an accurate reflection of the training load when the number of reps, number of sets, and loads are altered within routine training. There are advantages of using SRPE rather than objective measures. A principle benefit is convenience. Athletes need only provide a single subjective assessment of the global difficulty of their workout. Future research should directly assess the functionality of SRPE across the duration of a periodized training program.
REFERENCES 1. Baechle, TR and Earle, RW. Essentials of Strength Training and Conditioning. Champaign, IL: Human Kinetics, 2008. 2. Borg, GAV. Psychophysical bases of perceived exertion. Med Sci Sports Exerc 14: 377–381, 1982. VOLUME 28 | NUMBER 7 | JULY 2014 |
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Work Distribution Influences SRPE 3. Coutts, A, Murphy, A, Pine, M, Reaburn, P, and Impellizzeri, F. Validity of the session-RPE method for determining training load in team sport athletes. J Sci Med Sport 6: 525, 2003. 4. Day, ML, McGuigan, MR, Brice, G, and Foster, C. Monitoring exercise intensity during resistance training using the session RPE scale. J Strength Cond Res 18: 353–358, 2004. 5. Farah, BQ, Lima, AH, Lins-Filho, OL, Souza, DJ, Silva, GQ, Robertson, RJ, Cyrino, ES, and Ritti-Dias, RM. Effects of rest interval length on rating of perceived exertion during a multiple-set resistance exercise. Percept Mot Skills 115: 273–282, 2012. 6. Foster, C. Monitoring training in athletes with reference to overtraining syndrome. Med Sci Sports Exerc 30: 1164–1168, 1998. 7. Foster, C, Florhaug, JA, Franklin, J, Gottschall, L, Hrovatin, LA, Parker, S, Doleshal, P, and Dodge, C. A new approach to monitoring exercise training. J Strength Cond Res 15: 109–115, 2001. 8. Foster, C, Heimann, KM, Esten, PL, Brice, G, and Porcarid, JP. Differences in perceptions of training by coaches and athletes. S Afr J Sports Med 8: 3–7, 2001. 9. Gearhart, RF Jr, Goss, FL, Lagally, KM, Jakicic, JM, Gallagher, J, and Robertson, RJ. Standardized scaling procedures for rating perceived exertion during resistance training. J Strength Cond Res 15: 320–325, 2001. 10. Green, JM, Yang, Z, Laurent, CM, Davis, J-K, Kerr, K, Pritchett, RC, and Bishop, PA. Session RPE following interval and constantresistance cycling in hot and cool environments. Med Sci Sports Exerc 39: 2051–2057, 2007. 11. Hornsby, J, Green, J, O’Neal, E, Killen, L, McIntosh, J, and Coates, T. Influence of terminal RPE on session RPE. J Strength Cond Res 27: 2800–2805, 2013. 12. Impellizzeri, FM, Rampinini, E, Coutts, AJ, Sassi, A, and Marcora, SM. Use of RPE-based training load in soccer. Med Sci Sports Exerc 36: 1042–1047, 2004. 13. Kraft, JA, Green, JM, and Thompson, K. Session RPE responses during resistance training bouts equated for total work but differing in work rate. J Strength Cond Res. [Epub ahead of print] doi: 10.1519/JSC.0b013e31829b569c. 14. Lagally, KM, McCaw, ST, Young, GT, Medema, HC, and Thomas, DQ. Ratings of perceived exertion and muscle activity during the bench press in recreational and novice lifters. J Strength Cond Res 18: 359–364, 2004. 15. Larson, GD Jr and Potteiger, JA. A comparison of three different rest intervals between multiple squat bouts. J Strength Cond Res 11: 115–118, 1997.
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16. Lomax, RG. An Introduction to Statistical Concepts for Education and Behavioral Sciences. Mahwah, NJ: Lawrence Erlbaum Associates, 2001. 17. McGuigan, MR, Dayel, AA, Tod, D, Foster, C, Newton, RU, and Pettigrew, S. Use of session rating of perceived exertion for monitoring resistance exercise in children who are overweight or obese. Pediatr Exerc Sci 20: 333–341, 2008. 18. McGuigan, MR, Egan, AD, and Foster, C. Salivary cortisol responses and perceived exertion during high intensity and low intensity bouts of resistance exercise. J Sports Sci Med 3: 8–15, 2004. 19. Minganti, C, Ferragina, A, Demarie, S, Verticchio, N, Meeusen, R, and Piacentini, MF. The use of session RPE for interval training in master endurance athletes: Should rest be included? J Sports Med Phys Fitness 51: 547–554, 2011. 20. Minganti, C, Capranica, L, Meeusen, R, and Piacentine, MF. The validity of session rating of perceived exertion method for quantifying training load in teamgym. J Strength Cond Res 24: 3063–3068, 2010. 21. Minganti, C, Capranica, L, Meeusen, R, and Piacentine, MF. The use of session-RPE method for quantifying training load in diving. Int J Sports Physiol Perform 6: 408–418, 2011. 22. Pritchett, RC, Green, JM, Wickwire, PJ, Pritchett, KL, and Kovacs, MS. Acute and session RPE responses during resistance training: Bouts to failure at 60% and 90% of 1RM. S Afr J Sports Med 21: 23–26, 2009. 23. Robertson, RJ. Perceived Exertion for Practitioners: Rating Effort with the Omni Picture Scale. Champaign, IL: Human Kinetics, 2004. 24. Singh, F, Foster, C, Tod, D, and McGuigan, MR. Monitoring different types of resistance training using session rating of perceived exertion. Int J Sports Physiol Perform 2: 34–45, 2007. 25. Smilios, I, Pilianidis, T, Karamouzis, M, and Tokmakidis, SP. Hormonal responses after various resistance exercise protocols. Med Sci Sports Exerc 35: 644–654, 2003. 26. Suminski, RR, Robertson, RJ, Arslanian, S, Kang, J, Utter, AC, DaSilva, SG, Goss, FL, and Metz, KF. Perception of effort during resistance exercise. J Strength Cond Res 11: 261–265, 1997. 27. Sweet, TW, Foster, C, McGuigan, MR, and Brice, G. Quantification of resistance training using the session rating of perceived exertion method. J Strength Cond Res 18: 796–802, 2004. 28. Thomas, S, Reading, J, and Shephard, RJ. Revision of the Physical Activity Readiness Questionnaire (PAR-Q). Can J Sport Sci 17: 338–345, 1992. 29. Wallace, LK, Slaterrey, KM, and Coutts, AJ. The ecological validity and application of the session-RPE method for quantifying training loads in swimming. J Strength Cond Res 23: 33–38, 2009.
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Journal of Strength and Conditioning Research
Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
AND
TYLER M. GAST1
Department of Health, Physical Education and Recreation, Missouri Western State University, St Joseph, Missouri; and Department of Health, Physical Education and Recreation, University of North Alabama, Florence, Alabama
ABSTRACT Kraft, JA, Green, JM, and Gast, TM. Work distribution influences session ratings of perceived exertion response during resistance exercise matched for total volume. J Strength Cond Res 28(7): 2042–2046, 2014—Session ratings of perceived exertion (SRPE) are sensitive to changes in total work volume and work rate during resistance training. This study examined the influence of work distribution (varied load, set, and repetitions [reps]) on SRPE in 2 resistance exercise trials matched for total work volume (sets 3 reps 3 percentage of 1 repetition maximum [% 1RM]) and work rate (total work volume/time). Participants completed a low load/high rep (LLHR) trial (2 sets 3 12 reps 3 3-minute recovery at ;60% 1RM) and a high load/low rep (HLLR) trial (3 sets 3 6 reps 3 1.5-minute recovery at ;80% 1RM) of the bench press, lat pull-down, overhead press, upright row, triceps extension, and biceps curl. A 2-minute recovery separated each exercise in both trials. Session ratings of perceived exertion and recovery heart rate (HR) were recorded 20 minutes after exercise. Preset and postset RPE and HR were higher for HLLR vs. LLHR (3.1 6 1.6; 104 6 15 b$min21 vs. 2.1 6 1.3; 98 6 10 b$min21) and (5.5 6 0.9; 139 6 14 b$min21 vs. 4.4 6 0.9; 131 6 12 b$min21), respectively. Session RPE was higher for HLLR (5.7 6 1.4) vs. LLHR (4.3 6 1.4) with no difference in recovery HR. Session ratings of perceived exertion was greater with higher load despite matched total volumes and work rates. Higher preset acute RPE and HR in HLLR may indicate differences in recovery between sets. Higher postset acute RPE and HR in HLLR indicated increased difficulty of individual sets in HLLR, which likely contributed to SRPE differences. Practitioners can be confident that SRPE accurately reflects changes in training load
Address correspondence to Justin A. Kraft, [email protected]. 28(7)/2042–2046 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
2042
the
when the number of sets, reps, and loads are altered within routine training.
KEY WORDS RPE, strength training, training load INTRODUCTION
T
he session ratings of perceived exertion (SRPE) is a subjective measure of global training load. It is postulated that the SRPE represents as “gestalt” experience, which incorporates a variety of physiological and perceptual cues into a single global marker of exercise intensity (2,21). As such, the SRPE has been shown to be a versatile measure capable of validly assessing exercise intensity in exercise paradigms that are intermittent in nature including resistance exercise (4,7,10,12,18–21,24,27). Although SRPE has been validated in numerous settings, relatively little is known about the precise factors that contribute to the gestalt experience reflected in SRPE. Session RPE may be influenced by a number of metabolic and physiologic factors (metabolic acidosis, etc.), which may vary as exercise parameters such as intensity, repetitions (reps), and recovery period are changed (27). Early research indicated that intensity (as measured by percentage of 1 repetition maximum [1RM]) was a key mediating factor and that SRPE increased with increases in the percentage of 1RM lifted (4,18,27). However, Pritchett et al. (22) reported higher SRPE at lower relative resistance (% 1RM) during resistance training to failure, noting that participants performed more total volume of work at lower intensities. This led authors to conclude that total volume lifted was a principle mediating factor. More recent work has examined the influence of work rate (total volume lifted per unit time) on SRPE response during resistance training by comparing 3 resistance exercise protocols: (a) 3 sets 3 8 reps 3 60% 1RM 3 1.5-minute recovery between sets, (b) 2 sets 3 12 reps 3 60% 1RM 3 3-minute recovery between sets, and (c) 3 sets 3 8 reps 3 60% 1RM 3 3-minute recovery between sets. Results indicated that SRPE was linked more closely to changes in work rate than to the number of sets and reps per set (13). Additionally, authors noted a trend (p = 0.08) toward increased
TM
Journal of Strength and Conditioning Research
Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
the
TM
Journal of Strength and Conditioning Research SRPE when performing higher reps and fewer sets despite lifting equal volumes. Authors also noted higher postset acute RPE in this condition (likely resulting from completing more total work per set) and postulated that the difficulty of individual sets may serve as a mediating factor influencing SRPE and warrants further investigation (13). One limitation was that load was held constant in the study at 60% of 1RM in all protocols. Therefore, the purpose of this study was to examine the influence of the independent variable work distribution (varied load, set, and reps) on the dependent variable SRPE during 2 resistance exercise trials matched for total work volume and work rate.
METHODS Experimental Approach to the Problem
A within-subjects repeated-measures design was used to examine the influence of the independent variable (work distribution) on the dependent variable SRPE during 2 resistance training protocols matched for total volume and work rate (total volume/unit time) across the entire bout. Work distribution was manipulated by varying reps, sets, and resistance as a unit. These 3 variables are often altered concurrently in natural settings (i.e., increases in load naturally prompt a reduction in reps), yet the influence on perceptual responses is not well understood. Participants completed an initial session that included the determination of a 1RM for the bench press, lat pull-down, overhead press, upright row, triceps press down, and barbell curl. Participants additionally completed 2 experimental trials consisting of performing the aforementioned exercises according to following protocols: (a) low load/high rep (LLHR) 2 sets 3 12 reps 3 3-minute rest at ;60% of 1RM and (b) high load/low rep (HLLR) 3 sets 3 6 reps 3 1.5-minute rest at ;80% of 1RM. Exercises were performed in the order listed and trials were counterbalanced. One warm-up set of 12 reps with ;40% of the predetermined 1RM was performed before the bench press. This was followed by a 2-minute recovery period. No warm-up was performed before other exercises. A standard 2-minute rest period was provided between all exercises in both trials. These 2 protocols were designed to equate workloads (offset the decrease in reps 3 set 3 6 reps = 18 reps vs. 2 set 3 12 reps = 24 reps with a proportional increase in intensity [80 vs. 60% 1RM]). Additionally, recovery periods between sets were designed to equate total recovery time across the entire exercise bout. Therefore, both total exercise trial duration and duration of each exercise within the trial were constant (i.e., 2 sets 3 12 reps 3 60% 1RM with 3-minute rest required an equivalent time as 3 sets 3 6 reps 3 80% 1RM with 1.5-minute rest). In this way, work completed per unit time (i.e., work rate) was controlled between trials. As such, work distribution was isolated as the independent variable. The selection of the 60 and 80% intensity levels was based on the rep to load relationship set forth by the National Strength and Conditioning Association (1) and selected to ensure that
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participants could complete all reps in both trials, which was necessary for matching total volume. Subjects
Fourteen recreationally strength-trained (strength training $ 2 times per week for a minimum of 6 weeks) male volunteers between the ages of 18 and 25 years (age, 20.8 6 1.7 years; height, 180 6 5 cm; weight, 81.9 6 13.3 kg; percent body fat, 11.6 6 4.9%) were recruited. A prerequisite of 6 uninterrupted weeks of training before study inclusion ensured a minimal level of resistance training experience and ensured that differences in RPE would not result from changes in strength attributable to our exercise protocol. All participants received a clear explanation of the study and signed a written informed consent before participation. Procedures were approved a priori by the local institutional review board for the protection of human subjects. All participants were screened before the study for physical problems contraindicating physical activity (Physical Activity Readiness Questionnaire [PAR-Q]) (28). All subjects were nonsmokers. Participants were instructed to continue with their normal diet (including dietary vitamins/supplements) through the duration of the study to decrease likelihood of confounding potential of nutritional changes during participation. Participants were instructed to report for testing in a well-hydrated state, 1.5–3 hours after their last meal, to refrain from resistance exercise on the day prior (;24–48 hours) and all strenuous physical activity ;24 hours before testing and to avoid caffeine on the day of testing. Procedures
Participants reported for testing on 3 occasions. During the first trial, they completed a health questionnaire and informed consent and were measured for descriptive data (age [years], height [cm], weight [kg], and percent body fat using an Omron body fat analyzer, Omron Healthcare Inc., Bannockburn, IL, USA). A 1RM was then determined for each of the 6 exercises performed in experimental trials. Participants then returned on separate days and completed the 2 counterbalanced resistance training protocols: (a) LLHR 2 sets 3 12 reps 3 3-minute rest at ;60% of 1RM and (b) HLLR 3 sets 3 6 reps 3 1.5-minute rest at ;80% of 1RM. During experimental trials, heart rate (HR) via polar HR monitor (Polar Inc., Port Washington, NY) and acute ratings of perceived exertion (RPE) were measured before (preset) and after (postset) each set. Session RPE (global exercise RPE) and recovery HR were recorded 20 minutes after bout completion. All perceived exertion ratings were estimated according to the 10-point omni scale for resistance training (23). This scale is comprised of a visual scale with verbal anchors for estimating feelings of exertion. Preset RPE was a measure of perceived vigor (no actual exertion at moment recorded) and was measured by having participants respond to the question “How do you feel?” The preset RPE was designed to assess subjective feelings of “preparedness” or “acute recovery.” The RPE scale was used for this measure VOLUME 28 | NUMBER 7 | JULY 2014 |
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Work Distribution Influences SRPE thereby avoiding additional rating scales, which may have introduced confusion for participants. Preset RPE has previously been used to assess recovery while investigating the influence of 3 different rest intervals during a multiset squat routine (15). Session RPE was estimated by asking participants the question, “How was your workout?” (6). This variable provides a subjective estimate of the global difficulty of the entire exercise bout.
RESULTS
One Repetition Maximum Determination
DISCUSSION
Exercises were performed in the following order: bench press, lat pull-down, overhead press, upright row, triceps press down, and barbell curl. The 1RM was defined as the heaviest weight the participant was able to lift for 1 complete repetition (24). Determination of the 1RM was performed according to the procedure outlined by Baechle and Earle (1). Participants performed a light warm-up with a resistance they estimated they could lift 5–10 times. After a 1-minute rest, the participant performed a second warm-up using a weight they estimated they could lift 3–5 times. Twominute rest was provided. At this time, the participant estimated a near maximal load (one they expected to perform 2 or 3 times) and performed the final warm-up followed by 3-minute rest. The load was increased to an estimated maximum (add 10–20 lbs for upper body) and a 1RM was attempted. If successful, 3-minute rest was provided and an additional attempt was made with a new estimated weight. If unsuccessful, 3-minute rest was provided and another attempt was made with a reduced load. Loads were adjusted based on participant feedback with the goal of identifying the 1RM within 3–5 attempts. A 3-minute rest was allowed between exercises.
Preset and postset RPE and HR values are listed in Table 1. Preset and postset RPE and HR averaged across the exercise trials were significantly higher for HLLR vs. LLHR. Session RPE was significantly higher for HLLR (5.7 6 1.4) vs. LLHR (4.3 6 1.4) with no difference in recovery HR (HLLR: 88 6 17 b$min21 vs. LLHR: 89 6 10 b$min21).
Session RPE increased with higher load despite matched total volumes and work rates. This indicates that intensity may be a primary mediating factor responsible for SRPE estimations and corresponds with previous findings that reported higher SRPE as resistance (as a %1RM) increased (4,18,27). However, it should be noted that total volume lifted was equated between trials as previous research has shown that differences in total volume of weight lifted may overshadow intensity in determining SRPE (22). An alternative explanation is that the difficulty of individual sets within a resistance exercise bout may partially mediate SRPE responses. Higher postset HR was observed in HLLR vs. LLHR, which indicated greater physiological strain during individual sets in HLLR. The increased strain was reflected in higher postset RPE in HLLR. Thus, participants also perceived individual sets as more difficult in HLLR than LLHR. The increased difficulty of individual sets in HLLR likely contributed to SRPE differences and indicates that the difficulty of individual sets within a resistance exercise bout contributes to the overall estimation of difficulty reflected in SRPE. Perceptual measures represent a culmination of input from multiple sources. As such, Statistical Analyses current results do not indicate that difficulty experienced in A 6 exercise 3 2 protocol repeated-measures analysis of an individual set is the only or even the dominant mediator variance was used to detect difference among trials for for SRPE. However, responses do suggest a link. These preset RPE, postset RPE, preset HR, postset HR (averaged findings coincide with previous work from our laboratory across trials). Bonferroni follow-up tests (16) were used to showing a trend toward higher SRPE after completing 2 sets assess pairwise comparisons (set by set). A paired t-test was 3 12 reps 3 60% 1RM vs. 3 sets 3 8 reps 3 60% 1RM of the used to determine differences in SRPE and recovery HR. same 6 exercises (13). In this study, higher postset RPE was Differences were considered significant at the p # 0.05 level associated with the protocol containing a greater number of (2-tailed test). sets and lower reps per set, whereas in Kraft et al. (13) greater postset RPE occurred during the protocol containing fewer sets but higher reps per TABLE 1. Pre- and postset average acute ratings of perceived exertion and heart set. In other words, increases in rate by exercise protocol.* SRPE seem to be associated Preset HR Postset HR with higher postset RPE. Condition Preset RPE Postset RPE (b$min21) (b$min21) Combining these 2 results would indicate that the strain LLHR 2.1 6 1.3 4.4 6 0.9 98 6 10 131 6 12 (as reflected in postset RPE) HLLR 3.1 6 1.6† 5.5 6 0.9† 104 6 15† 139 6 14† within the individual sets has *RPE = ratings of perceived exertion; HR = heart rate; LLHR = low load/high rep; HLLR = a stronger link with SRPE than high load/low rep. reps per set or number of sets. †LLHR vs. HLLR (p # 0.05). It is also plausible that greater strain resulted in concomitant
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the
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Journal of Strength and Conditioning Research changes in physiological variables (i.e., pH) potentially linked with elevations in SRPE. However, in this study, direct evidence supporting this notion is lacking. This interpretation may also help explain the influence of load on SRPE as both acute RPE (4,9,14,26,27) and SRPE (4,18,27) have been reported to increase as intensity (%1RM lifted) increases. It should be noted that resistance exercise in the current paradigm included a fixed end point. It has been postulated that during resistance exercise with fixed termination criteria, load (%1RM) may play a more critical role as participants will likely focus on the heaviness of the lift rather than actual exertion when estimating RPE (13,22). Pritchett et al. (22) reported higher acute RPE and SRPE during light intensity (60% 1RM) vs. high intensity (90% 1RM) resistance exercise to failure and attributed this to the completion of a greater volume of work completed in each exercise in the lower intensity trial. In this study, higher postset RPE was associated with the HLLR trial despite completing less work per set in this trial. Even so, higher SRPE did correspond with higher postset RPE in both studies and corroborates previous research, which concluded that average RPE and SRPE are complimentary measures (4). Still, interpreting the influence of postset RPE on SRPE should be done with caution as previous research has noted that average acute RPE and SRPE are not identical measures and that SRPE seems to provide different (17,24) (or perhaps additional) information. Previous resistance training research has indicated differences in salivary cortisol response during low intensity (30% 1RM) and high intensity (75% 1RM) exercise (18) and has also shown that altering the number of sets influences hormonal response to resistance exercise (25). Research comparing matched volumes of interval cycling to constant load cycling noted higher levels of blood lactate during interval exercise, which corresponded to higher SRPE after interval cycling (10). A similar mechanism may apply to the current findings as higher postset RPE in HLLR may also indicate a greater metabolic disruption within the HLLR exercise protocol thus contributing to the difference in SRPE, although this is speculative and was not measured in this study. Higher postset HR similarly attests to greater physiological demands in HLLR. Preset HR and RPE were significantly affected by set distribution, resistance, and recovery period. Ratings of perceived exertion (measured after the first rep of a set) has been shown to increase with shorter rest intervals leading authors to conclude that RPE can be considered a valid measure of muscle recovery (5). Other studies have assessed recovery through the estimation of preset RPE (13,15). For example, Larson and Potteiger (15) used preset RPE to examine the influence of 3 different recovery periods during a multiset squat (reps to failure) resistance protocol and concluded that similar preset RPE values despite different recovery parameters indicated similar recovery between conditions. In contrast, higher preset RPE and HR in HLLR indicated
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reduced recovery between sets vs. LLHR in this study. Differences in recovery between sets may have been attributable to differing metabolic disruption in the HLLR protocol indicated by higher postset RPE as postulated above. Thus, the shorter recovery period between sets in HLLR likely inhibited participants’ ability to recover as effectively (vs. LLHR) for similar performance in subsequent efforts. Differences in SRPE despite no difference in recovery HR indicate that SRPE is sensitive to variation in work distribution but is estimated independently of recovery HR. When originally developed, it was suggested that SRPE be estimated 30 minutes after exercise to prevent terminal exercise conditions from influencing the estimation (4,7,8,27). It has since been shown that RPE at exercise endpoint does not influence SRPE (11) and that SRPE estimations recorded 15 minutes or greater after exercise termination do not differ (13,24).
PRACTICAL APPLICATIONS The ability to quantify exercise load significantly influences the development and implementation of strategies designed to maximize training-induced benefits (3,29). However, traditional measures of training load, such as HR, are inadequate during intermittent activity comprised high intensity bouts with recovery periods interspersed such as resistance training (7). Additionally, these methods often present a practical barrier in the form of the time and equipment required for monitoring. As such, a valid alternative method that can quantify training load in a single marker is of great practical benefit to coaches and practitioners (7,8). The SRPE provides this alternative measure. This study expands the understanding of the factors that mediate SRPE responses. Results indicate that load is a primary mediating factor during resistance exercise to fixed termination criteria (i.e., number of sets and reps). It further confirms that postset RPE measurements compliment the SRPE (4). Therefore, both acute postset RPE and SRPE provide a viable alternative to objective markers of intensity during resistance exercise. The SRPE appears to be a highly sensitive marker, which responds to a variety of training parameters which are often manipulated during the course of training. Practitioners can thus be confident that SRPE provides an accurate reflection of the training load when the number of reps, number of sets, and loads are altered within routine training. There are advantages of using SRPE rather than objective measures. A principle benefit is convenience. Athletes need only provide a single subjective assessment of the global difficulty of their workout. Future research should directly assess the functionality of SRPE across the duration of a periodized training program.
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