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A novel scale to assess resistance-exercise effort a
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Daniel A. Hackett , Nathan A. Johnson , Mark Halaki & Chin-Moi Chow
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Discipline of Exercise and Sports Science, University of Sydney, Lidcombe, New South Wales, Australia Published online: 09 Aug 2012.
To cite this article: Daniel A. Hackett , Nathan A. Johnson , Mark Halaki & Chin-Moi Chow (2012): A novel scale to assess resistance-exercise effort, Journal of Sports Sciences, 30:13, 1405-1413 To link to this article: http://dx.doi.org/10.1080/02640414.2012.710757
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Journal of Sports Sciences, September 2012; 30(13): 1405–1413
A novel scale to assess resistance-exercise effort
DANIEL A. HACKETT, NATHAN A. JOHNSON, MARK HALAKI, & CHIN-MOI CHOW Discipline of Exercise and Sports Science, University of Sydney, Lidcombe, New South Wales, Australia
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(Accepted 5 July 2012)
Abstract In this study, we examined the validity of a novel subjective scale for assessing resistance-exercise effort. Seventeen male bodybuilders performed five sets of 10 repetitions at 70% of one-repetition maximum, for the bench press and squat. At the completion of each set, participants quantified their effort via the rating of perceived exertion (RPE) and novel estimatedrepetitions-to-failure scales, and continued repetitions to volitional exhaustion to determine actual-repetitions-to-failure. There were high correlations between estimated- and actual-repetitions-to-failure across sets for the bench press and squat (r 0.93; P 5 0.05). During sets 3, 4, and 5, estimated-repetitions-to-failure predicted the number of repetitions to failure for the bench press and squat, as indicated by smaller effect sizes for differences (ES ¼ 0.37–0.0). The estimated-repetitionsto-failure scale was reliable as indicated by high intraclass correlation coefficients (0.92) and narrow 95% limits of agreement (0.63 repetitions) for both the bench press and squat. Despite high correlations between RPE and actualrepetitions-to-failure (P 5 0.05), RPE at volitional fatigue was less than maximal for both exercises. Our results suggest that the estimated-repetitions-to-failure scale is valid for predicting onset of muscular failure, and can be used for the assessment and prescription of resistance exercise.
Keywords: Resistance training, RPE scale, training intensity, weight-lifting
Introduction It is well documented that resistance training is associated with several health benefits and aids in the optimization of health and longevity (Winett & Carpinelli, 2001). For those involved in sport, resistance training is usually undertaken as part of an overall training programme to reduce injury risk and improve performance in another task (Stone, 1990). In contrast, for individuals involved in bodybuilding and weight-lifting, resistance exercise forms the major component of a training programme (Kraemer & Ratamess, 2004). The design of a resistance training programme involves manipulation of acute programming variables, including the type of exercise, order of exercise, number of sets, recovery period, and load (Ratamess et al., 2009). The intensity of resistance exercise is generally expressed according to the load used (ACSM, 2009). For example, as a percentage of the maximal load that could be lifted only once (i.e. percentage of one-repetition maximum), or through using a load that limits a lifter to a specific number of repetitions
before reaching muscular failure (i.e. repetition maximum). Another accepted method to assess the intensity of resistance exercise is the rating of perceived exertion (RPE) scale (ACSM, 2009). This scale assesses subjective effort, strain, discomfort, and fatigue during exercise. The most common scales are: the 6–20 category RPE scale (Borg, 1970) and 0–10 category ratio scale (Noble, Borg, Jacobs, Ceci, & Kaiser, 1983). The latter is considered to be more useful for assessing resistance-exercise intensity (Day, McGuigan, Brice, & Foster, 2004; Naclerio et al., 2011; Sweet, Foster, McGuigan, & Brice, 2004). It has been suggested that resistance exercise intensity is most accurately assessed as perceived effort applied for a given load, defined as the number of repetitions performed in relation to the number possible (Fisher, Steele, Bruce-Low, & Smith, 2011). This is based on data that have shown large variations in the number of repetitions performed to muscular failure at the same percentage of onerepetition maximum (Hoeger, Hopkins, Barette, & Hale, 1990; Shimano et al., 2006). Previous studies
Correspondence: D. A. Hackett, Discipline of Exercise and Sports Science, University of Sydney, 75 East Street, Lidcombe, NSW 2141, Australia. E-mail:
[email protected] ISSN 0264-0414 print/ISSN 1466-447X online Ó 2012 Taylor & Francis http://dx.doi.org/10.1080/02640414.2012.710757
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have demonstrated that active muscle RPE is related to the load used during resistance exercise, with RPE increasing with the load expressed as a percentage of one-repetition maximum (Gearhart et al., 2002; Lagally et al., 2001). However, several investigators have reported RPE less than maximum during resistance exercise to volitional fatigue, indicating a mismatch between RPE and maximal effort. For instance, in resistance-trained individuals who performed lifts to muscular failure at 60% and 90% of one-repetition maximum, mean RPE (0–10 category ratio scale) values were 7.2 and 6.8 (Shimano et al., 2006) and 8.1 and 6.8 (Pritchett, Green, Wickwire, Pritchett, & Kovacs, 2009) respectively. Therefore, the RPE scale might be useful with loads, but is less suitable for assessing effort to muscular failure. Perception of effort during resistance exercise is influenced by several exertional sensations, including muscle activation, afferent signals from golgi tendon organs, muscle spindles and mechanoreceptors (Cafarelli, 1982; Jones & Hunter, 1983; McCloskey, Gandevia, Porter, & Colebatch, 1983). This is unlike aerobic exercise, where there are strong correlations between physiological responses (i.e. heart rate, rate of oxygen consumption, muscle blood lactate) and perception of effort (Borg, 1970, 1973; Noble et al., 1983). However, similar to resistance exercise, a limitation of RPE occurs with aerobic exercise, as large inter-individual variability in RPE responses have been documented at the same relative intensities of exercise (Garcin, Vautier, Vandewalle, Wolff, & Monod, 1998). This led to the development of a second perceptually based scale that subjectively estimates time to exhaustion (estimated-time-limit scale) to help assess aerobic exercise performance (Garcin & Billat, 2001; Garcin, Coquart, Robin, & Matran, 2011; Garcin, Vandewalle, & Monod, 1999). A similar scale for resistance exercise whereby a lifter estimates repetitions to muscular failure after a set could improve ways to express relative strain over RPE. Feedback provided would be useful for bodybuilders and weight-lifters to assess effort during sets when not lifting to muscular failure, and could therefore help with the planning of training. In addition, this scale could help athletes tailor their resistance-training programme to avoid overtraining and injuries, as a result of excessive training and/or inadequate recovery. The purpose of this study was to determine the validity of a novel subjective estimated-repetitions-tofailure scale for predicting muscular failure during resistance exercise. To do this, we compared estimated-repetitions-to-failure with actual-repetitionsto-failure and related both to RPE across multiple resistance-exercise bouts in experienced resistancetrainers.
Methods Participants Seventeen competitive male bodybuilders (8.2 + 3.2 years of resistance training experience; age 32.3 + 4.7 years; body mass 89.1 + 5.4 kg; stature 178.5 + 4.5 cm; one-repetition maximum 148 + 11 kg and 208 + 22 kg for bench press and squat, respectively) participated in the study. On the basis of questionnaire data, all participants performed 5–6 sessions of resistance training per week involving 2–3 muscle groups trained per session (split-training routine), 12–16 sets per muscle group per session (3–4 sets per exercise) at loads equivalent to 8- to 12-repetition maximum or 70–80% of one-repetition maximum. All participants reported regular use of both the bench press and squat in their normal training routine. In addition, all participants reported not having taken any banned substances as declared by the International Olympic Committee (2008) antidoping rules, and were free of musculoskeletal injuries or conditions when the study took place. The study received approval from the University of Sydney Human Research Ethics Committee. Experimental design Each participant visited the laboratory on four occasions, twice for one-repetition maximum testing and two experimental sessions. Participants were instructed to maintain their normal diet during the days preceding visits, to consume their last meal at least 2 h before exercise, and to avoid using preworkout supplements because of their possible influence on perceptual responses (Blomstrand, 2001). Moreover, participants were instructed to refrain from exercises that targeted muscle groups used for the bench press and squat in the 48 h before one-repetition-maximum testing. Habituation and experimental sessions were separated by 48 h to minimize confounding influences of previous exercise. The exercise protocol used to assess the RPE and estimated-repetitions-to-failure scales consisted of performing five sets of 10 repetitions at 70% of one-repetition maximum with 5 min recovery between sets both for the bench press and squat. These exercises were selected because they are routinely performed in resistance-training programmes and are commonly used to assess muscular strength of the upper and lower body, respectively. All exercises were undertaken at a controlled speed (no ballistic movements) through the full range of motion. This involved full extension during the lifting phase for all lifts, while during the lowering phase the bar was moved to chest level (bench press), or to a position where the thighs were parallel to the floor (squat).
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A novel scale to assess resistance-exercise effort One-repetition maximum testing The one-repetition-maximum tests for the bench press and squat were performed in accordance with the American College of Sports Medicine’s guidelines for exercise testing and prescription (ACSM, 2009). Briefly, participants performed a warm-up that comprised 8–10 repetitions using a light load, 6–8 repetitions using a moderate load, and 2–3 repetitions using a heavy load. After the warm-up, participants began one-repetition-maximum testing by increasing the load and attempting to lift the load once. If this lift was successful, the participant recovered for 5 min before attempting another lift with a heavier load. This cycle was continued until the participant was unable to complete a lift using proper technique through the full range of motion. One-repetition maximum was defined as the heaviest load that was successfully lifted for each exercise (technical error of measurement ¼ 1.6 and 3.9 kg equivalent to 1.1% and 2.3% for the bench press and squat exercises, respectively). Creation of the estimated-repetitions-to-failure scale The estimated-repetitions-to-failure scale was designed as an integer scale from 0 to 10, with each interval representing one repetition. The 0–10 range was selected to span the anticipated number of repetitions that individuals could complete after 6– 12 repetitions at loads that ranged from 70 to 85% of one-repetition maximum (Shimano et al., 2006). At the highest end of the scale (corresponding to a score of ‘‘10’’) was the descriptor ‘‘or greater’’, which indicated more repetitions possible before muscular failure and was selected to keep the scale concise.
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report their perceived effort (RPE scale), and estimate the number of repetitions that they could perform to muscular failure (estimated-repetitions-to-failure scale). Both the RPE and estimated-repetitions-tofailure scales were written on a board and placed directly above the participants while they were supine for the bench press and in front of them during the squats. From the RPE scale, participants were asked: ‘‘How would you rate your effort for the set?’’ A rating of 0 was associated with ‘‘no effort’’ (rest), and a rating of 10 was considered to be maximal exertion to the point of volitional muscular fatigue (Table I). From the estimated-repetitions-to-failure scale, participants were asked: ‘‘How many additional repetitions could you have performed?’’ For example, a 0 indicated that the participant estimated that no additional repetitions could be completed (muscular failure reached) (Table II).
Table I. Modified version of the 0–10 category-ratio rating of perceived exertion (RPE) scale used for this study. Rating
Descriptor
0 1 2 3 4 5 6 7 8 9 10
Rest Very, very easy Easy Moderate Somewhat hard Hard – Very hard – – Maximal
Note: The verbal anchors have been changed slightly (e.g. light becomes easy; strong or severe becomes hard). The participants were shown this scale at the conclusion of the exercise set and asked: ‘‘How would you rate your effort for the set?’’
Habituation session After the one-repetition-maximum test session, a copy of both the RPE and estimated-repetitions-to-failure scales was provided to each participant. All participants received verbal and written instruction on the use of the RPE and estimated-repetitions-to-failure scales. To help participants link their full exercise stimulus range with their full RPE and estimatedrepetitions-to-failure response range, a memory-anchoring procedure was used. This involved asking each participant to think of times during training when they reached exertion that was equal to the verbal cues at the bottom and top of the scales. Perceived exertion was assessed via the modified 0–10 category-ratio RPE scale used in previous resistancetraining studies (Day et al., 2004; Egan, Winchester, Foster, & McGuigan, 2006; Sweet et al., 2004). The habituation session involved participants following the same protocol as used in the experimental session. At the completion of each set, participants were asked to
Table II. Estimated-repetitions-to-failure scale. Estimated-repetitions-to-failure 10 or greater 9 8 7 6 5 4 3 2 1 0 Note: The participants were shown this scale at the conclusion of the exercise set and asked: ‘‘How many additional repetitions could you have performed?’’ An estimated-repetitions-to-failure score of ‘‘10 or greater’’ indicated that the participant estimated that 10 or more repetitions could be completed, while a ‘‘0’’ indicated that the participant estimated no additional repetitions could be completed (muscular failure reached).
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Experimental session The experimental session began with each participant performing a warm-up that comprised 8–10 repetitions of a moderate load for each exercise before the first set of the bench press and squat. After the warm-up, participants performed five sets of 10 repetitions (or to muscular failure if 10 repetitions was not possible) at 70% of one-repetition-maximum, for both exercises. During the lifts, participants were encouraged to complete each repetition through a full range of motion without deviating from the proper technique, while keeping the lifting speed constant. Two spotters were present to provide verbal encouragement and ensure adherence to correct technique and safety of participants. Both RPE and estimated-repetitions-to-failure were recorded upon completion of each set, with the order in which participants reported these ratings randomized between sets. The experimenter was blinded to randomization. During the reporting of RPE and estimated-repetitions-to-failure, the barbell remained supported by the participant at the top of the concentric phase. Therefore, participants achieved full extension of the elbow joint while supine for the bench press, and full extension of the knee joint while upright for the squat. These positions were held for approximately 5 s, after which the participant performed repetitions to volitional exhaustion. During this part of the set, verbal encouragement was given to each participant to perform as many repetitions as possible. This was referred to as the actual-repetitions-to-failure and was indicated by the inability to perform the concentric phase of a lift. Once muscular failure was achieved, spotters were required to remove the load safely from the participant. Statistical analysis Since the estimated-repetitions-to-failure scale was ‘‘0’’ to ‘‘10 or greater’’, any actual-repetitions-tofailure value that was 410 was adjusted to 10. Data for all recordings are presented as means + standard deviations (s). Data were analysed using Statistica v.10.0 (StatSoft Inc., Tulsa, AZ). Parametric tests compared estimated- and actual-repetitions-to-failure since the data were interval, normally distributed (confirmed using probability plots), and had similar variances. Relationships between estimated- and actual-repetitions-to-failure across participants for each exercise were assessed using Pearson’s correlations and linear least-products regression (Ludbrook, 1997). Estimated- and actual-repetitions-to-failure for each exercise were assessed by a fully within-groups factorial analysis of variance (ANOVA). Tukey post hoc tests were used as appropriate. The reliability of participants’ accuracy in estimating repetitions-to-
failure between the habituation and the experimental sessions was determined via the intraclass correlation coefficient (a two-way random-effects model). As a general rule, an intraclass correlation coefficient above 0.90 is considered to be high and shows a consistency of measurements across trials. In addition, the reliability was assessed using Bland and Altman’s 95% limits of agreement as described by Atkinson and Nevill (1998). The relationships between both estimated- and actual-repetitions-to-failure with RPE were analysed using a Spearsman’s rank correlation because RPE is a non-parametric variable. Statistical significance was set at P 5 0.05 and effect sizes (ES) were evaluated as per the scale: 0.2, 0.5, and 0.8 representing small, medium, and large effect sizes respectively (Cohen, 1992). Results For both the bench press and squat, the estimatedand actual-repetitions-to-failure for set 5 was 0 for all participants. Therefore, data from set 5 were excluded from the ANOVA. Estimated- and actualrepetitions-to-failure decreased across sets for both bench press (F3,48 ¼ 81.5; P 5 0.01; large ES 2.2) and squat (F3,48 ¼ 42.7; P 5 0.05; large ES 1.2). Actual-repetitions-to-failure was greater than estimated equivalents for the bench press (F1,16 ¼ 27.9; P 5 0.01) and squat (F1,16 ¼ 6.8; P 5 0.05). There was an interaction between estimated- and actual-repetitions-to-failure across sets both for the bench press (F3,48 ¼ 5.0; P 5 0.01) and squat (F3,48 ¼ 33.4; P 5 0.01). Post hoc testing showed that actual-repetitions-to-failure were greater than estimated equivalents for sets 1 and 2 (P 5 0.01; small and medium ES ¼ 0.65 and 0.49, respectively) for the bench press, and set 1 (P 5 0.01; medium ES ¼ 0.76) for the squat, with no differences between estimated- and actual-repetitions-to-failure for all other sets (P 0.21; small ES 0.37) (Table III and Figure 1). The intraclass correlation coefficient for the accuracy of participants’ estimates of the repetitions to failure between the habituation session and the experimental session ranged from 0.92 to 1.0 for the bench press and 0.96 to 1.0 for the squat, indicating high reliability. The 95% limits of agreement between sessions ranged from 0.63 to 0.0 (mean 0.18 + 1.25) repetitions for the bench press and from 0.45 to 0.0 (mean 0.04 + 1.13) repetitions for the squat, again indicating good agreement. There were positive correlations between estimated- and actual-repetitions-to-failure across all participants for the bench press (r ¼ 0.95; P 5 0.05) and squat (r ¼ 0.93; P 5 0.05) (Figure 2). There were also positive correlations for individual participants between estimated- and actual-repetitions-to-
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A novel scale to assess resistance-exercise effort Table III. The 95% confidence interval (CI) and effect sizes (ES) for mean estimated- and actual-repetitions-to-failure. Estimated-repetitions-to-failure Set
Difference
mean
s
95% CI
mean
s
95% CI
mean
ES (Cohen’s d)
5.8 4.2 2.4 1.4 0.0
2.2 1.5 1.4 1.5 0.0
[4.6–6.9] [3.4–4.9] [1.6–3.1] [0.7–2.2] [0–0]
7.1 4.9 2.7 1.5 0.0
1.9 1.7 1.3 1.5 0.0
[6.1–8.0] [4.1–5.8] [2.1–3.4] [0.7–2.3] [0–0]
1.3 0.8 0.4 0.1 0.0
0.65 0.49 0.27 0.04 –
5.1 4.0 3.5 2.1 0.0
2.6 2.1 1.3 1.1 0.0
[3.8–6.5] [2.9–5.1] [2.8–4.2] [1.5–2.7] [0–0]
7.1 4.4 3.1 1.8 0.0
2.6 2.4 0.9 1.1 0.0
[5.7–8.4] [3.1–5.6] [2.6–3.6] [1.3–2.4] [0–0]
1.9 0.4 70.4 70.3 0.0
0.76 0.16 0.37 0.28 –
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Bench press 1 2 3 4 5 Squat 1 2 3 4 5
Actual-repetitions-to-failure
Figure 1. Estimated- and actual-repetitions-to-failure values for the bench press (A) and squat (B) (mean + s). *Significant difference between estimated- and actual-repetitions-to-failure.
failure across sets 1 to 5 for the bench press (r ¼ 0.97 + 0.04; P 5 0.05) and squat (r ¼ 0.90 + 0.11; P 5 0.05). For the bench press, negative correlations were observed between estimated-repetitions-to-failure and RPE (Spearman’s rho ¼ 70.96 + 0.03; P 5 0.05) and actual-repetitions-to-failure and
Figure 2. Scatter plot showing the relationship between estimatedand actual-repetitions-to-failure for the bench press (A) and squat (B). The lines of best fit, r2, and the least-products regression equations are shown. Note that the slopes are close to 1 and the intercepts are close to 0.
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RPE (Spearman’s rho ¼ 70.96 + 0.03; P 5 0.05) for individual participants. For the squat, there were negative correlations between estimated-repetitionsto-failure and RPE (Spearman’s rho ¼ 70.86 + 0.15; P 5 0.05) and actual-repetitions-to-failure and RPE (Spearman’s rho ¼ 70.94 + 0.05; P 5 0.05) for individual participants. The RPE at volitional exhaustion (set 5) was 8.9 + 0.8 and 9.0 + 0.7 for the bench press and squat, respectively.
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Discussion The purpose of this study was to design and evaluate a novel ‘‘estimated-repetitions-to-failure’’ scale to assess resistance-exercise effort. We recorded both the estimated- and actual-repetitions-to-failure across five sets of exercise in experienced resistance trainers. The results showed high positive correlations between estimated- and actual-repetitions-tofailure across all participants, and from individual participants across all sets. During sets 3, 4, and 5, estimated-repetitions-to-failure accurately predicted the number of repetitions to failure for the bench press and squat as indicated by no differences with small effect sizes (Table III). However, the estimated-repetitions-to-failure scale was less accurate (underestimated by a mean of approximately one repetition) in predicting repetitions to failure during sets 1 and 2 for the bench press, and set 1 for the squat, as indicated by the interaction of rating with time (Figure 1) and medium effect sizes (Table III). These findings suggest that the estimated-repetitions-to-failure scale is valid for predicting repetitions to failure, although slightly less accurate during the earlier sets of an exercise when participants are probably less fatigued. In addition, the high intraclass correlation coefficient and narrow limits of agreement for the accuracy of participants’ estimating repetitions to failure between the habituation and the experimental sessions indicated that the estimated-repetitions-to-failure scale had good reliability. Importantly, the estimated-repetitions-to-failure scale accurately predicted the point of muscular failure. In contrast, and in line with previous reports (ACSM, 2009; Pritchett et al., 2009; Shimano et al., 2006), despite being positively correlated with estimated- and actual-repetitions-to-failure, mean RPE was less than 10 at the point of muscular failure. The RPE is a widely accepted method for assessing resistance-exercise effort (ACSM, 2009). Previous studies have demonstrated that active muscle RPE ratings increase with the lifting of heavier loads and as an individual approaches fatigue (Duncan & AlNakeed, 2006; Gearhart et al., 2002; Lagally et al., 2001). However, an intriguing aspect of the RPE scale is that muscular failure is often achieved with ratings less than ‘‘maximal’’ effort (RPE ¼ 10)
reported (Pritchett et al., 2009; Shimano et al., 2006). Yet prediction and identification of muscular failure is required for assessing resistance-exercise effort and for prescription of training loads (i.e. repetition maximum) (Kraemer & Ratamess, 2004; Ratamess et al., 2009; Wilardson, 2007). Furthermore, the number of repetitions performed in a set in relation to the number possible is suggested to be the most accurate method to assess resistance-exercise intensity (Fisher et al., 2011). Therefore, a scale based on the aerobic exercise ‘‘estimated-time-limit’’ scale was designed for resistance exercise. For experienced resistance-trainers in the present study, the estimated-repetitions-to-failure scale was valid for predicting the repetitions to muscular failure during resistance exercise. However, participants underestimated the number of repetitions they could complete to muscular failure during the earlier sets of the exercises. Similar to perceived exertion, estimation of repetitions to failure probably involves the interplay of afferent and efferent feedback, as well as psychological and situational factors (Eston, 2009). In the earlier sets, participants could have relied on past experience as opposed to recent experience to make their estimations. Therefore, it was not surprising that as the sets progressed, the accuracy of the participants’ estimation increased. Despite the differences between the estimated- and actualrepetitions-to-failure for the earlier sets of exercise, the difference was approximately only one repetition, indicating that participants only slightly underestimated this. The ACSM recommendations for muscular strength and hypertrophy suggest that 60–85% of one-repetition maximum for 8–12 repetitions should be performed for novice and intermediate individuals, and 70–100% of one-repetition maximum for 1–12 repetitions for advanced resistance-trainers (Ratamess et al., 2009). However, the number of repetitions to muscular failure at a fixed percentage of one-repetition maximum varies between muscle groups (Arazi & Asadi, 2011; Hoeger et al., 1990), with more repetitions generally required for larger muscles. In addition, inter-individual variation in intensity and effort probably occurs when performing a specific number of repetitions at a fixed percentage of one-repetition maximum (Hoeger et al., 1990). For example, at 70% of one-repetition maximum, one individual might perform 12 repetitions to failure, whereas another might perform 18 repetitions to failure. If both of these individuals performed 10 repetitions at 70% of one-repetition maximum, each would be training at different levels of effort. Resistance-trainers could use the estimated-repetitions-to-failure scale to assess the onset of muscular failure after an exercise. For example, performing 10 repetitions of the bench press at 70% of
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A novel scale to assess resistance-exercise effort one-repetition maximum could result in the estimation of two or eight repetitions to muscular failure. If a lifter’s intention is to perform multiple sets of this exercise in a specific repetition range, an estimation of two repetitions to failure would inform the lifter of the need to increase recovery between sets. In contrast, an estimation of eight repetitions to failure indicates that a greater load is required to achieve a specific intensity and effort for the set. Whether sets should be performed to muscular failure is a topic of enthusiastic debate. Some investigators have demonstrated that training to failure is superior for increases in strength and hypertrophy (Drinkwater et al., 2005; Rooney, Herbert, & Balnave, 1994), whereas others concluded that it is not necessary (Folland, Irish, Roberts, Tarr, & Jones, 2002; Kramer et al., 1997; Sanborn et al., 2000). Prescription of resistance exercise based on training to failure can be expressed as a repetition maximum or as the maximal repetitions to failure at a fixed percentage of one-repetition maximum (Kraemer & Ratamess, 2004; Ratamess et al., 2009; Tan, 1999). However, performing consecutive sets to failure reduces the force that a muscle can generate, with reductions in exercise load required to maintain a specific number of repetitions (Izquierdo et al., 2006; Rahimi, 2005). Therefore, an effective strategy to maintain a specific number of repetitions at a fixed load is to select a load that requires slightly less than maximal effort for the first set (Wilardson, 2007). Resistance-trainers could use the estimated-repetitions-to-failure scale to select an appropriate load that would result in muscular failure during the final set. For example, for a session involving three sets of 10 repetitions, if the lifter estimated 7 repetitions to failure after the first set performed with 100 kg, the load could be adjusted to 110 kg. This would reduce estimated repetitions to failure by 2 on the subsequent set, and because of increasing fatigue, lead to absolute failure on the final set. In addition, for individuals with pre-existing musculoskeletal injuries or cardiovascular conditions for which training to failure is contraindicated (Stone, Chandler, Conley, Kramer, & Stone, 1996), the estimated-repetitions-to-failure scale could be a useful way to avoid this outcome. Prolonged training to failure could lead to overtraining and overuse injuries (Stone et al., 1996; Wilardson, 2007). Athletes using resistance exercise as part of their overall training programme could use the estimated-repetition-to-failure scale to indicate if they are overreaching and require more recovery. This would be seen by fewer repetitions to muscular failure estimated during the initial set of an exercise despite the repetitions and load remaining the same as in previous sessions. The load could then be adjusted to correspond to greater repetitions to muscular failure estimated at a specific repetition
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range. The scale could also be useful for assessing improvements in muscular strength, whereby increased strength would be indicated by more repetitions to muscular failure estimated for sets of the same exercise between training sessions. A scale similar to estimated-repetitions-to-failure could be used to assess the occupational capability of injured workers. Rather than estimate repetitions to failure for a resistance exercise, the scale could be modified to estimate the ability to perform specific manual tasks. For example, the number of boxes or bricks that could be lifted before pain or fatigue occurred. Employers could use this information to determine the capabilities of an injured employee or safety of a task. Further research is needed to examine the suitability of the procedure in applications such as these. The high accuracy in estimating repetitions to failure could have been because participants were attuned to sensations of effort as a result of their exercise experience. Garcin et al. (2011) demonstrated that high-standard cyclists were better at estimating time to exhaustion than low-standard cyclists. It was postulated that high-standard athletes are accustomed to signals of exertion associated with exercise and use these as cues to estimate exercise limits (Garcin et al., 2011). Therefore, it is possible that the estimated-repetitions-to-failure scale might not be valid for novice resistance-trainers. Research is required to assess the validity of this scale in different groups. We cannot exclude the possibility that the accuracy in estimation of repetitions to failure was influenced by goals set by individual participants. Namely, participants could have used their estimation as a goal, and once this was achieved, motivation to continue was lost. However, all participants in this study were highly experienced resistance-trainers who commonly perform additional repetitions after reaching muscular fatigue with the help of spotters or by reducing the load. Therefore, it is unlikely that the participants ceased sets because they achieved their estimated repetitions rather than reaching muscular failure. Furthermore, participants received equal encouragement in all tests, and had spotters to assist when muscular failure resulted. All together, this supports the contention that the estimated-repetitions-to-failure scale is valid for predicting repetitions to failure for resistance exercise. However, further research in a larger sample size of experienced resistance-trainers is required to confirm its broader validity. Conclusion The estimated-repetitions-to-failure scale is a valid method for reporting estimated repetitions to failure
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during resistance exercise. High positive correlations between estimated-repetitions-to-failure and actualrepetitions-to-failure occurred across sets. Participants slightly underestimated repetitions to muscular failure during the earlier sets (by approximately one repetition), although they accurately predicted repetitions to muscular failure during the later sets. The estimated-repetitions-to-failure scale could be useful for assessing intensity at a fixed percentage of onerepetition maximum between individuals, targeting sets to produce muscular failure, assessing effort for individuals with pre-existing musculoskeletal injuries or cardiovascular conditions, and assessing whether athletes are overreached and need further recovery. Research is required to determine the appropriateness of the estimated-repetitions-to-failure scale for novice resistance-trainers.
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