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A novel scale to assess resistance-exercise effortDaniel A. Hackett

a, Nathan A. Johnson

a, Mark Halaki

a& Chin-Moi Chow

a

aDiscipline 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

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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

(Accepted 5 July 2012)

Abstract

In this study, we examined the validity of a novel subjective scale for assessing resistance-exercise effort. Seventeen malebodybuilders performed five sets of 10 repetitions at 70% of one-repetition maximum, for the bench press and squat. At thecompletion of each set, participants quantified their effort via the rating of perceived exertion (RPE) and novel estimated-repetitions-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;P5 0.05). During sets 3, 4, and 5, estimated-repetitions-to-failure predicted the number of repetitions to failurefor the bench press and squat, as indicated by smaller effect sizes for differences (ES 0.370.0). The estimated-repetitions-to-failure scale was reliable as indicated by high intraclass correlation coefficients (0.92) and narrow 95% limits ofagreement (0.63 repetitions) for both the bench press and squat. Despite high correlations between RPE and actual-repetitions-to-failure (P5 0.05), RPE at volitional fatigue was less than maximal for both exercises. Our results suggest thatthe estimated-repetitions-to-failure scale is valid for predicting onset of muscular failure, and can be used for the assessmentand prescription of resistance exercise.

Keywords: Resistance training, RPE scale, training intensity, weight-lifting

Introduction

It is well documented that resistance training isassociated 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 manipula-

tion 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 ofperceived exertion (RPE) scale (ACSM, 2009).

This scale assesses subjective effort, strain, discom-

fort, and fatigue during exercise. The most common

scales are: the 620 category RPE scale (Borg, 1970)

and 010 category ratio scale (Noble, Borg, Jacobs,

Ceci, & Kaiser, 1983). The latter is considered to be

more useful for assessing resistance-exercise inten-

sity (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 numberof 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 one-

repetition 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]

Journal of Sports Sciences, September 2012; 30(13): 14051413

ISSN 0264-0414 print/ISSN 1466-447X online 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. Forinstance, in resistance-trained individuals who

performed lifts to muscular failure at 60% and

90% of one-repetition maximum, mean RPE (010

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 inten-

sities of exercise (Garcin, Vautier, Vandewalle,

Wolff, & Monod, 1998). This led to the developmentof 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 athletestailor 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-to-

failure scale for predicting muscular failure during

resistance exercise. To do this, we compared esti-

mated-repetitions-to-failure with actual-repetitions-

to-failure and related both to RPE across multiple

resistance-exercise bouts in experienced resistance-

trainers.

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 question-

naire data, all participants performed 56 sessions of

resistance training per week involving 23 muscle

groups trained per session (split-training routine),

1216 sets per muscle group per session (34 sets per

exercise) at loads equivalent to 8- to 12-repetition

maximum or 7080% 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) anti-

doping 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 pre-workout 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 be-tween 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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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 Medicines guide-

lines for exercise testing and prescription (ACSM,

2009). Briefly, participants performed a warm-up

that comprised 810 repetitions using a light load,

68 repetitions using a moderate load, and 23repetitions 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 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 de-

signed as an integer scale from 0 to 10, with each

interval representing one repetition. The 010 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, whichindicated more repetitions possible before muscular

failure and was selected to keep the scale concise.

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 partici-

pants 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 estimated-

repetitions-to-failure response range, a memory-an-choring 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 010

category-ratio RPE scale used in previous resistance-

training 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

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-to-

failure 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, parti-

cipants 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 010 category-ratio rating of

perceived exertion (RPE) scale used for this study.

Rating Descriptor

0 Rest

1 Very, very easy

2 Easy

3 Moderate

4 Somewhat hard

5 Hard

6

7 Very hard

8

9

10 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?

Table II. Estimated-repetitions-to-failure scale.

Estimated-repetitions-to-failure

10 or greater

9

8

7

65

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 partici-

pant performing a warm-up that comprised 810

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-max-imum, for both exercises. During the lifts, partici-

pants 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 re-

corded upon completion of each set, with the order

in which participants reported these ratings rando-

mized 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. Dur-

ing 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-to-

failure 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-failuresince 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 Pearsons correla-

tions 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 addi-

tion, the reliability was assessed using Bland and

Altmans 95% limits of agreement as described byAtkinson and Nevill (1998). The relationships be-

tween both estimated- and actual-repetitions-to-fail-

ure with RPE were analysed using a Spearsmans rank

correlation because RPE is a non-parametric variable.

Statistical significance was set at P5 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 estimated-

and actual-repetitions-to-failure for set 5 was 0 for all

participants. Therefore, data from set 5 were

excluded from the ANOVA. Estimated- and actual-

repetitions-to-failure decreased across sets for both

bench press (F3,48 81.5; P5 0.01; large ES

2.2) and squat (F3,48 42.7; P5 0.05; large

ES 1.2). Actual-repetitions-to-failure was greater

than estimated equivalents for the bench press

(F1,16 27.9; P5 0.01) and squat (F1,16 6.8;

P5 0.05). There was an interaction between

estimated- and actual-repetitions-to-failure across

sets both for the bench press (F3,48 5.0;

P5 0.01) and squat (F3,48 33.4; P5 0.01). Posthoc testing showed that actual-repetitions-to-failure

were greater than estimated equivalents for sets 1 and

2 (P5 0.01; small and medium ES 0.65 and

0.49, respectively) for the bench press, and set 1

(P5 0.01; medium ES 0.76) for the squat, with

no differences between estimated- and actual-repeti-

tions-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, indicatinghigh 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 esti-

mated- and actual-repetitions-to-failure across all

participants for the bench press (r 0.95;P5 0.05)

and squat (r 0.93; P5 0.05) (Figure 2). There

were also positive correlations for individual partici-

pants between estimated- and actual-repetitions-to-


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failure across sets 1 to 5 for the bench press (r

0.97 + 0.04; P5 0.05) and squat (r 0.90 +

0.11; P5 0.05).

For the bench press, negative correlations were

observed between estimated-repetitions-to-failure

and RPE (Spearmans rho 70.96 + 0.03;

P5 0.05) and actual-repetitions-to-failure and

Table III. The 95% confidence interval (CI) and effect sizes (ES) for mean estimated- and actual-repetitions-to-failure.

Es timated-repetitions-to-failure Actual-repetitions-to-failure Difference

Set mean s 95% CI mean s 95% CI mean ES (Cohens d)

Bench press

1 5.8 2.2 [4.66.9] 7.1 1.9 [6.18.0] 1.3 0.65

2 4.2 1.5 [3.44.9] 4.9 1.7 [4.15.8] 0.8 0.49

3 2.4 1.4 [1.63.1] 2.7 1.3 [2.13.4] 0.4 0.274 1.4 1.5 [0.72.2] 1.5 1.5 [0.72.3] 0.1 0.04

5 0.0 0.0 [00] 0.0 0.0 [00] 0.0

Squat

1 5.1 2.6 [3.86.5] 7.1 2.6 [5.78.4] 1.9 0.76

2 4.0 2.1 [2.95.1] 4.4 2.4 [3.15.6] 0.4 0.16

3 3.5 1.3 [2.84.2] 3.1 0.9 [2.63.6] 70.4 0.37

4 2.1 1.1 [1.52.7] 1.8 1.1 [1.32.4] 70.3 0.28

5 0.0 0.0 [00] 0.0 0.0 [00] 0.0

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.

Figure 2. Scatter plot showing the relationship between estimated-

and 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 (Spearmans rho 70.96 + 0.03; P5 0.05)

for individual participants. For the squat, there were

negative correlations between estimated-repetitions-

to-failure and RPE (Spearmans rho 70.86 +

0.15; P5 0.05) and actual-repetitions-to-failure

and RPE (Spearmans rho 70.94 + 0.05; P5

0.05) for individual participants. The RPE at voli-

tional exhaustion (set 5) was 8.9 + 0.8 and 9.0 +0.7 for the bench press and squat, respectively.

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 correla-

tions between estimated- and actual-repetitions-to-

failure 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 esti-

mated-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-repeti-

tions-to-failure scale is valid for predicting repeti-tions to failure, although slightly less accurate during

the earlier sets of an exercise when participants are

probably less fatigued. In addition, the high intra-

class correlation coefficient and narrow limits of

agreement for the accuracy of participants estimat-

ing repetitions to failure between the habituation and

the experimental sessions indicated that the esti-

mated-repetitions-to-failure scale had good reliabil-

ity. 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 withestimated- 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 & Al-

Nakeed, 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 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). Further-

more, the number of repetitions performed in a set in

relation to the number possible is suggested to be themost 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, estima-

tion 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 actual-

repetitions-to-failure for the earlier sets of exercise,

the difference was approximately only one repetition,

indicating that participants only slightly underesti-

mated this.

The ACSM recommendations for muscularstrength and hypertrophy suggest that 6085% of

one-repetition maximum for 812 repetitions should

be performed for novice and intermediate indivi-

duals, and 70100% of one-repetition maximum for

112 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 percentageof 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-repeti-

tions-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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one-repetition maximum could result in the estima-

tion of two or eight repetitions to muscular failure. If

a lifters intention is to perform multiple sets of

this exercise in a specific repetition range, an esti-

mation 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 toachieve 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, & Bal-

nave, 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 sessioninvolving 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 over-training 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

range. The scale could also be useful for assessing

improvements in muscular strength, whereby in-

creased 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 tofailure 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 oc-

curred. 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 applica-

tions 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) demon-

strated 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 accu-

racy in estimation of repetitions to failure wasinfluenced by goals set by individual participants.

Namely, participants could have used their estima-

tion 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, thissupports the contention that the estimated-repeti-

tions-to-failure scale is valid for predicting repeti-

tions to failure for resistance exercise. However,

further research in a larger sample size of experi-

enced 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 actual-

repetitions-to-failure occurred across sets. Partici-

pants slightly underestimated repetitions to muscular

failure during the earlier sets (by approximately one

repetition), although they accurately predicted repe-

titions to muscular failure during the later sets. The

estimated-repetitions-to-failure scale could be usefulfor assessing intensity at a fixed percentage of one-

repetition 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 appropriate-

ness of the estimated-repetitions-to-failure scale for

novice resistance-trainers.

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