Initially proposed for use during submaximal exercises and considered to be related to the exercising heart rate, the rating of perceived exertion (RPE) has also been used as a measure of the exercise intensity during resistance exercises (1,13,18). The RPE may be related to the percentage of the maximal strength (1 repetition maximum [1RM]) that is activated by the exercise and should be used to provide estimates of the 1RM (9,28,32). Several authors suggest that the RPE allows the prescription of appropriate and individualized intensities during resistance exercise saving training time and optimizing the individual responses to training (9,13,32). Furthermore, one study reports that session RPE could accurately quantify the intensity of an entire strength training session (7).
However, during submaximal aerobic exercises, the RPE has been reported to be influenced by many exercise parameters including intensity, duration, work-recovery ratio, fitness, and subjects' previous experience (12,15,30). Recently, some studies investigating submaximal running exercises have shown that the RPE increases relatively to the percentage of distance completed or yet to be completed (10,15,23). In resistance exercise, the intensity is set by the load to lift, and the volume is determined by the number of repetitions performed with high differences occurring in the individual capacity to repeat lifts (8,15). In few studies, the influence of resistance exercise volume on the RPE has not been observed (25,29). Other studies, investigating the RPE regulation during resistance exercises, have controlled the volume of the exercise by regulating the absolute total load lifted (7,13,26) or by monitoring the total work by multiplying the percentage of 1RM by the repetitions number (19). These latter methods do not seem to account for the nonlinear evolution of strength and the interindividual variations in strength endurance. Consequently, previous studies investigating perceived exertion during resistance exercises compared the RPE after exhaustive exercise in heavy resistance tests (i.e., 4–5 repetitions at 90% of 1RM) to RPE after easier exercise in moderate resistance ones (i.e., 12 repetitions at 30% of 1RM). Recent studies on aerobic exercises suggested that the RPE has scalar time-based properties that allow the prediction of time to exhaustion (5,15,22). As a result, the RPE during resistance exercise may describe the exercise volume performed in relation to the maximal volume rather than the absolute volume itself. Moreover, the RPE set the physical performance by comparing the current exercise bout with previous experience, taking into account the athlete's current fitness and the environmental conditions (10,15). Well-trained subjects could improve their perceived exertion during resistance exercises by comparison with their own capabilities and previous experiences as observed previously in aerobic exercises (11,21,33). Scientists, athletes, and coaches use the RPE during resistance exercise session to identify the relative intensity of the lifts without considering a possible influence of exercise volume on the rating. We assumed that the use of the RPE during resistance exercises should be improved and better understood after the identification of exercise volume and athletes training state influences on RPE.
The aim of this study was to investigate how the RPE during resistance exercises was influenced by the athlete's training state and by the relative exercise volume.
Experimental Approach to the Problem
Each participant underwent 3 laboratory-based sessions in the morning (from 9.30 to 11.30 AM) of the same day (from Tuesday to Friday) over a 3-week period. The participants were instructed to (a) not undertake resistance exercises 48 hours before each session; (b) not eat in the 2 hours before the sessions exercise testing; (c) not use alcohol and caffeine, in the last 24 hours before testing. During the first visit, the subjects warmed up and were instructed how to use the RPE scale. Thereafter, trials to determine the 1RM benchpress lift were performed. During the second visit, the subjects performed a test to measure the maximum number of repetition (MNR) he or she could achieve when lifting heavy and moderate loads.
In the third session, multilift sets of bench presses were performed. Because one aim of the study was to assess the training effect on RPE, the protocol of this session reduced the possible influence of a best anticipatory activity intrained athletes (best comparison of their own capacities to the load to lift) by a different means than was previously reported (blindfolded subjects) (10): The weights to be liftedwere covered using a large plastic bag containing Styrofoam particles to ensure that the subjects did not know, before they lifted the weight, what was the load to lift.
Each subject performed 4 sets of bench-press lifts: the firstand second sets involved a lowMNR percentage, in a random order, at moderate and heavy loads used in MNR tests; the third and fourth sets involved a highMNR percentage, first at the heavy load and then at the moderate load because this set was the more exhausting one. Each set was interspersed by a 6-minute recovery pause. These multilift sets used load ranges instead of specific intensities because ranges better described the strength continuum and were easier to manage because they did not require to adapt precisely the loads to liftfor each subject that was particularly uneasy according to the large population and blinded loads of this study.
A total of 80 physical education students (55 men and 25 women, 22.1 ± 1.2 years old), trained in numerous sports, recruited from the University campus volunteered to participate in this study. This population included 3 groups with different states of strength training determined after subjects' interview conducted by the investigators: the first group (n = 29; 19 men and 10 women) was composed of subjects regularly involved in strength training programs composed of miscellaneous methods (from weight circuit training to eccentric supramaximal sets) prescribed principally to enhance their experience in physical training (24.2 ± 2.3 strength training sessions in the previous 3 months); the second group (n = 26; 18 men and 8 women) was composed of subjects less-well trained but with a good technical control of the bench-press lift (8.7 ± 2.8 strength training sessions in the previous 3 months); the third group (n = 25; 18 men and 7 women) comprised novices who had not participated in any form of resistance exercise before the trial began. The study took place 3–4 months after the beginning of the training season, with no competitive events scheduled. In the 3 weeks preceding the study, novices were technically prepared for the bench-press lifts over 3 specific training sessions. The participants were informed of the experimental risks and signed an informed consent document before the investigation. The study was approved by the consultative committee for participants' protection in clinical research (Paris university, France).
One Repetition Maximum Bench-Press Test
The 1RM strength for the bench press was measured using a free-weight Olympic bar and plates. The 1RM performances were used to determine individual moderate and heavy loads used in the second and third visits. Before the test, the subjects were instructed on the standardized technique to lift the load. Proper technique included the following requirements: (a) that the subjects lie horizontally on the back and minimizing the arch of the lower back; (b) that the subjects hold the bar with the hands placed slightly wider than the shoulder width; (c) that the subjects lower the bar to touch their chest and then push it to full arms length away from the body. Spotters assisted the participant in lifting the bar from the support rack. Before the test, the subjects performed several warm-up sets using light weights of their choice. Each participant attempted successive bench presses, starting at a weight agreed upon by both the subject and the investigator (starting from 25% of body weight in novice women to 50% of the estimated 1RM in strength trained individuals) and increasing the weight by increments based on the preceding attempts until 2 consecutive attempts were unsuccessful (increments from 1 to 5 kg). To reduce a possible fatigue effect, a maximum of 6 attempts was allowed for each subject. The 1RM was assumed as being the heavier load (to the nearest kilogram) the subject lifted. A recovery period of 4 minutes was allowed between trials.
Maximum Number of Repetition Bench-Press Test
The MNR was determined as the number of repetitions that were completed before either (a) the subject was unable to lift the bar to the full arms length or (b) when the pause between consecutive lifts was >2 seconds. The MNR performances were used thereafter to express the exercise volume relatively to individual capacities. The MNR was assessed for the moderate and heavy loads used in the single-lift session (Table 1). The duration of pauses between consecutive lifts was controlled using an electronic metronome (set at 30 b·min−1; Korg, Japan). A 15-minute recovery period was allowed between each test.
Ratings of Perceived Exertion Procedures
Perceived exertion was measured with a Borg category-ratio scale (e.g., 0–10; CR-10) (2), as previously realized during strength training studies (25), without numerical rating of 0.5 and using the categorical ratings from “no exertion at all” to “maximal exertion” to facilitate the subjects' ability to appreciate the effort involved.
The CR-10 scale was used and explained to the subjects at the beginning of the third exercise session: “You are about to undergo a weight lifting exercise test. The scale before you contains numbers from 0 to 10 and will be used to assess your perceptions of exertion while lifting these weights. The perception of physical exertion is defined as the subjective strain, discomfort, and fatigue that you feel during exercise. We use this scale so that you may translate into numbers your feelings of exertion while you exercise. The numbers on the scale represent a range of feelings from no exertion at all (0) to maximal exertion (10).”
Exercise Intensity and Volume Determination
Each load was calculated as a percentage of subjects' 1RM and was randomly assigned: moderate load from 60 to 80% of 1RM and heavy loads from 80 to 100% of 1RM (Table 1).
In the third session, the subjects performed 4 sets composed of varied numbers of bench-press lifts at moderate and heavy loads. The subjects first performed the sets inducing the low relative volumes, in a random order for the loads used (4.5 ± 1.1 reps for moderate and 1.3 ± 0.4 reps for the heavy load), which was categorized <60% of the MNR (mean of relative volume 41.1 ± 17 % of MNR). Second, the sets inducing the high relative volumes (moderate load:14.5 ± 2.1 reps; high load: 2.9 ± 0.6 reps) categorized >60% of MNR (mean of relative volume 79.6 ± 14% of MNR). For each set, the absolute volume was calculated as being the total load lifted (load lifted × number of repetitions).
For each test session, exercise parameters and the RPE between different training state groups were compared using the t-test, for quantitative variables and chi-square tests for qualitative variables.
For each test session, we assessed if exercise parameters (absolute and relative intensity, total load, and relative volume) and subjects' characteristics (gender and training groups) were independently associated with the RPE by general linear model (GLM; exercise parameters, subjects' characteristics were independent variables, and RPE was the dependent variable). Partial correlations were calculated to observe the relationship between the RPE and exercise parameters or exercise characteristics independently of the other significant effects. Standard errors of the estimates were calculated to observed the accuracy of the exercise parameter prediction by using the RPE. Quantitative variables are expressed as mean ± SD and qualitative variables as percentage. The level set for significance was p ≤ 0.05. All statistical analyses were performed using the Statistica 7.1 software package (Statsoft, Maisons–Alfort, France).
The 1RM differences appeared between gender and between the groups of training state: women vs. men (respectively, 33.5 ± 4.3 vs. 67.8 ± 13.4 kg; p < 0.001). The MNR tests resulted in 18.2 ± 5.2 repetitions for the moderate load in the total population sample (Figure 1). The MNR test performed with heavy loads resulted in 4.1 ± 2.6 repetitions in the total population sample. There was no difference between well-trained, less well-trained and novices groups in the MNR results for tests completed with the moderate load test (respectively, 18.4 ± 5.1 repetitions vs. 18.7 ± 4.9 vs. 17.7 ± 6.1; p = 0.08) nor for with the heavy load (respectively, 4.5 ± 6.1 repetitions vs. 4.3 ± 5.9 vs. 3.4 ± 5.8; p = 0.09). The total loads lifted (load lifted × number of repetitions) differed between low and high relative volume tests when performed at moderate load (respectively, 197.7 ± 67 vs. 636.5 ± 212 kg, p <0.001) and at heavy load (respectively, 70.3 ± 17.2 vs. 156.7 ± 53.7 kg, p <0.001).
The GLM describes similar results for the 2 sets involving low relative volumes. Absolute exercise intensity, total load lifted, and subjects' gender were without influence on the RPE, whereas training state groups (p = 0.01; Table 2) and relative volume performed (p = 0.001) were significantly related with the RPE (in the first set: adjusted R 2 = 0.37 and in the second set: adjusted R 2 = 0.34, p < 0.001; Figure 2). Standard errors of the estimated relative volume based on the RPE were 12.8% in the first set and 14.4% in the second set. Significant partial correlations from unchanged other parameters were obtained between the RPE and relative volume (in the first set r = 0.64 and in the second set r = 0.61; p < 0.01), and with the high trained group (in the first set r = 0.88 with p < 0.001 and in the second set r = 0.54, p < 0.01) but not with the 2 other training groups (novices, less well trained).
The results of the GLM were similar in the third and fourth sets. In the third and fourth sets, absolute exercise intensity, total load lifted, subjects' gender and training state groups were without any influence on the RPE, whereas relative volume performed was significantly related with the RPE (in the third set adjusted R 2 = 0.65 and in the fourth set adjusted R 2 = 0.78, p < 0.001). Standard errors of the estimated relative volume based on the RPE were 6.9% in the third set and 5.3% in the fourth set.
It is established that the RPE during aerobic exercise is related to the duration of the exercise bout and also to the exercise intensity (12). This study advances this knowledge by establishing that the RPE during resistance exercise is related to the relative exercise volume (15,23). In addition, our results show that the subjects' training state positively influences the relationship of the RPE with the relative exercise volume even when the load to be lifted is unknown before the first lift.
The statistical relationship between the RPE and relative exercise volume increases as the exercise volume increases. In addition, the prediction of the relative exercise volume using the RPE was improved in high volume tests. Such improved accuracy of tests involving high physical strain (here, a high MNR %) has been reported previously in studies with many different designs (13,20,27). This effect was independent of the exercise intensity (percentage of 1RM) and independent of the absolute exercise volume (total load lifted). The relative exercise volume performed at a given load may influence the RPE suggesting a superior integration of the multiple signals that generate the RPE when multiple lifts were performed (4,6,24). Repeated lifts could increase sensory feedbacks from the muscles improving the accuracy of the effort perception. As previously suggested for aerobic exercises, the uncertainty of the muscle power output required to complete the exercise (load to be lifted and lifts to repeat) may be progressively resolved as the end point of the exercise approaches (21,31,33). High relative volumes of the sets seem to have produced physiological strains that were similarly perceived by the subjects regardless of their training state (34). This result confirmed the findings of a previous study reporting that that RPE was related to relative exercise intensity without there being any difference between recreational and novices weight lifters (17).
Conversely, during low relative volume sets, the training state influenced the relationship between the relative volume and RPE with a significant relationship appearing only in well-trained subjects. In a previous study using open loop cycling exercises, the inability of the RPE to predict the end point of long-lasting exercises has already been reported (12). The authors attributed this inability to the low exercise intensity (60–73% of the maximal aerobic power), which enhanced the potential maximal duration of the exercises performed. In our protocol, and usually in strength training, the maximal exercise volumes or durations are largely shorter than in aerobic exercises (few seconds vs. several minutes). As a consequence, we could argue that, during strength training exercises, the relationship between the RPE and relative exercise volume depend on the individuals' training state associated with the exercise-induced level of strain. Trained athletes seem to have integrated better and earlier the sensory signals of the muscle activity. This result could be related to the best effort regulation of trained athletes as recently described in the first part of elite rowing races (3).
Contrarily to previous studies, we assume that standard errors of predicted relative volume about 12.8 and 14.4% observed in low relative volume tests are high for the practical use of the RPE as the only predictor of volume during resistance exercises (9,28). This assumption could be emphasized in competitive athletes who require a careful monitoring of their training program characteristics. Conversely, in high relative volume sets, as strength improvements in novices would be expected to occur rapidly after the beginning of a training program, the RPE may be a good indicator to monitor the variations of strength capacities (14,16).
In conclusion, this study shows that the RPE is a function of the volume of exercise that has been performed, relative to the total exercise volume of which the subject is capable. These findings suggest that the RPE might provide a useful method for regulating the exercise bout during resistance exercise. According to relationship levels and prediction accuracy, it could be assumed that high exercise-induced strain is needed for good perception of resistance effort. Training might improve the perceived exertion of the actual effort at the beginning of a multilift set allowing a best effort regulation as it occurs during aerobic exercise (3,33).
Our study supports the concept that, during multilift sets, the RPE describes the exercise volume compared with the MNR an individual is capable rather than the intensity or the absolute volume independently. However, an higher accuracy of relative volume prediction was provided by ratings of sets involving high relative volumes. In novices and less well-trained subjects, ratings from low relative volumes appeared inaccurate to describe the actual volume lifted.
Consequently, we could assume that coaches should mainly consider high ratings of perceived exertion (ratings at ± point 8 in a 10-point scale in our study) to estimate (a) the actual volume or physical strain induced by training sets; (b) the maximum number of lifts an individual is capable at a given load; (c) the training-induced changes in the ability to repeat lifts. Because large errors in the prediction of the relative exercise volume may appear when using the RPE, such assessment should be associated with time to time direct testing of individual capabilities in maximal strength and in strength endurance.
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Keywords:Copyright © 2012 by the National Strength & Conditioning Association.
effort perception; maximal strength; physical activity and exercise methodology