The Effect of Rest Interval Length on Multi and Single-Joint Exercise Performance and Perceived Exertion

Abstract

Senna, G, Willardson, JM, de Salles, BF, Scudese, E, Carneiro, F, Palma, A, and Simão, R. The effect of rest interval length on multi and single-joint exercise performance and perceived exertion. J Strength Cond Res 25(11): 3157–3162, 2011—The purpose of this study was to compare repetition performance and rating of perceived exertion (RPE) with 1-, 3-, or 5-minute rest intervals between sets of multi and single-joint resistance exercises. Fifteen resistance trained men (23.6 ± 2.64 years, 76.46 ± 7.53 kg, 177 ± 6.98 cm, bench press [BP] relative strength: 1.53 ± 0.25 kg·kg⁻¹ body mass) completed 12 sessions (4 exercises × 3 rest intervals), with each session involving 5 sets with 10 repetition maximum loads for the free weight BP, machine leg press (LP), machine chest fly (MCF), and machine leg extension (LE) exercises with 1-, 3-, 5-minute rest intervals between sets. The results indicated significantly greater BP repetitions with 3 or 5 minutes vs. 1 minute between sets (p ≤ 0.05); no significant difference was evident between the 3- and 5-minute rest conditions. For the other exercises (i.e., LP, MCF, and LE), significant differences were evident between all rest conditions (1 < 3 < 5; p ≤ 0.05). For all exercises, consistent declines in repetition performance (relative to the first set) were observed for all rest conditions, starting with the second set for the 1-minute condition and the third set for the 3- and 5-minute conditions. Furthermore, significant increases in RPE were evident over successive sets for both the multi and single-joint exercises, with significantly greater values for the 1-minute condition. In conclusion, both multi and single-joint exercises exhibited similar repetition performance patterns and RPE, independent of the rest interval length between sets.

Introduction

Resistance training involves the manipulation of different prescriptive variables. According to the American College of Sports Medicine (¹), the main prescriptive variables are the load intensity, number of sets and repetitions (i.e., volume), rest interval between sets, exercise order, repetition velocity, training frequency, and exercise selection. Among these variables, the rest interval between sets has received relatively less scientific examination compared to other training variables such as load intensity and volume. A recent research review indicated that different rest intervals between sets can produce different acute responses and chronic adaptations on the neuromuscular and endocrine systems (⁴).

Prior studies demonstrated that longer rest intervals between sets resulted in significantly greater repetitions than shorter rest intervals did (^{9,11-13,16-18}). Specifically, Willardson and Burkett (^16-18) demonstrated significant reductions in repetition performance for the back squat and bench press (BP) at multiple load intensities (8 repetition maximum [RM], 50 and 80% 1RM, and 15RM) when shorter rest intervals (i.e., 30 seconds to 1 minute) were used vs. longer rest intervals (2–5 minutes). Accordingly, other studies (^11,12) have also demonstrated significantly fewer repetitions when shorter rest intervals were used. However, only multijoint exercises (i.e., squat and BP) were examined within a single study and oftentimes, resistance training sessions may also involve single-joint exercises.

A recent position stand recommended that when emphasizing strength development, 2–3 minutes of rest should be prescribed between sets for multijoint exercises and 1–2 minutes for single-joint exercises (¹). However, to our knowledge, repetition performance for multi and single joint exercises has not been compared within a single study with different rest intervals between sets. Additionally, the rating of perceived exertion (RPE) has not been compared after performance of multi or single joint exercises with different rest intervals between sets. These comparisons would be important to improve resistance training prescription and the efficiency of a session to determine whether or not the extra rest time could be beneficial for additional repetitions based on the type of exercise (i.e., multi or single joint) and the training goal. When maximizing, strength is the goal, the ability to perform greater repetitions with a given load may enhance adaptational processes, leading to greater gains.

Therefore, the purpose of this study was to examine the validity of the position stand recommendation (¹) concerning rest intervals between sets for a sample of resistance trained men. We hypothesized that repetition performance (i.e., total repetitions added over multiple sets) would progressively increase as the rest interval between sets was increased for the multijoint exercises because of the larger muscle mass involved and potentially greater recuperation time needed. Conversely, repetition performance would not be different between rest interval conditions for the single-joint exercises. Additionally, the RPE would progressively decrease as the rest interval between sets increased and would not significantly differ between the multi and single-joint exercises when sets were performed with full repetition maximums.

Methods

Experimental Approach to the Problem

After familiarization and determination of 10RM loads for the free weight BP, machine leg press (LP), machine chest fly (MCF), and machine leg extension (LE), subjects performed 12 different training sessions (48 hours between sessions). A randomized within-subject design was used to determine the exercise (BP, LP, MCF, and LE) in combination with the rest interval (1, 3, or 5 minutes) for each session. All exercise sets were performed with full repetition maximums during each session with the predetermined 10RM load. The total number of repetitions and the RPE were recorded after each exercise set. In this study, BP and LP were considered the multijoint exercises, and MCF and LE were considered the single-joint exercises.

Subjects

Fifteen trained men participated in this study (23.6 ± 2.64 years, 76.46 ± 7.53 kg, 177 ± 6.98 cm, BP relative strength: 1.53 ± 0.25 kg·kg⁻¹ body mass) with the following inclusion criteria: (a) had performed resistance training for at least 1 year with a minimum frequency of 3 sessions per week; (b) could perform a BP at least 125% of their body mass; (c) did not perform any other physical activity for the duration of this study; (d) did not present any medical conditions that could influence the training program; and (e) had stated that they had not used any anabolic–androgenic steroids or other ergogenic substances that may enhance repetition performance. Before data collection, all subjects answered “no” to all questions on the Physical Activity Readiness Questionnare (PAR-Q) (¹⁴). All subjects read and signed an informed consent after being informed of the testing procedures according to the Declaration of Helsinki. The experimental procedures were approved by the Ethics Committee of Federal University of Rio de Janeiro.

Determination of 10 Repetition Maximum

After 2 sessions to ensure familiarization with all exercises and experimental procedures, subjects performed 4 testing sessions during which 10RM loads were assessed for each exercise. On the first visit, the BP and LE 10RM tests were performed, whereas on the second visit, the MCF and LP 10RM tests were performed. To establish reliability, an additional 2 visits were conducted. During the 10RM tests, each subject performed a maximum of 3 10RM attempts for each exercise with 5 minutes of rest between attempts. After the 10RM load for a specific exercise was determined, a 10-minute rest was instituted before the first 10RM attempt for the next exercise was performed. Each testing session was separated by 48 hours during which time participants were restricted from performing any structured exercise.

The greatest load lifted over the 2 days was considered the 10RM load. The 10RM testing protocol has been described previously (¹⁵). Standard exercise techniques were followed for each exercise (²). Briefly, to minimize the errors, the following strategies were adopted: (a) Standard instructions concerning the testing procedures were given to the participants before the test; (b) subjects received standardized instructions on exercise technique; (c) body position was held constant (i.e., hand width during BP and foot position during the LP test); (d) verbal encouragement was provided during the testing procedure; and (e) the mass of all plates and bars used was determined using a precision scale.

Experimental Procedures

Forty-eight to 72 hours after the last 10RM test, subjects performed the first of 12 different training sessions (48 hours between sessions). In each session, 5 sets with 10RM loads were performed; a randomized within-subject design was used to determine the exercise (BP, LP, MCF, and LE) in combination with the rest interval (1, 3, or 5 minutes) used in each session. The warm-up before each session consisted of 2 sets of 12 repetitions at 40% of 10RM load of the exercise being tested that day. A 2-minute rest interval was instituted after the second warm-up set before the first experimental set. Subjects were verbally encouraged to perform all 5 sets with full repetition maximums. No attempt was made to control the repetition velocity; however, subjects were required to use a smooth and controlled motion and a standardized range of motion. All visits were conducted at the same time of the day. The total number of repetitions completed and the Omni-Res RPE (⁷) were recorded after each set.

Statistical Analyses

The statistical analysis was initially done by the Shapiro–Wilk normality test and by the homocedasticity test (Bartlett criterion). All variables presented normal distribution and homocedasticity. A series of 1-way analyses of variance was conducted to assess differences in the total number of repetitions completed during each exercise session and the number of repetitions completed for each exercise set of each rest condition. In the case of significant main effects, further comparisons were made via Bonferroni post hoc analysis. The Friedman test was used to compare differences in the RPE between sets within the same rest condition and between rest conditions for each exercise. If necessary, a Dunn post hoc test was used for multiple comparisons.

Additionally, to determine the magnitude of the findings, effect sizes (ESs; the difference between the pretest score and the posttest score divided by the pretest SD) were calculated for each exercise set of each rest condition, and the thresholds proposed by Cohen (³) were applied to determine the magnitude of treatment effects. The level of significance was p ≤ 0.05. Prism software version 5.0 has been used for all statistical analysis (GraphPad, Inc, San Diego, CA, USA).

Results

Excellent test–retest reliability for each exercise was demonstrated via intraclass correlation coefficients (BP r = 0.92, LP r = 0.98, MCF r = 0.98, LE r = 0.97). In addition, a paired student t-test indicated no significant differences in the test–retest 10RM loads for each exercise.

Significantly greater BP repetitions were completed with 3 or 5 minutes vs. 1-minute rest between sets (p ≤ 0.05); no significant difference was evident between the 3- and 5-minute conditions. For the other exercises (i.e., LP, MCF, and LE), significant differences were evident between all rest conditions (1 < 3 < 5; p ≤ 0.05) for the total repetitions completed (Table 1). For all exercises, consistent declines in performance (relative to the first set) were observed for all rest conditions; starting with the second set for the 1-minute condition and the third set for the 3- and 5-minute conditions (Table 1 and Figure 1).

Table 1: Number of repetitions in each set and the total number of repetitions in each exercise with 1-, 3-, and 5-minute rest intervals (mean ± SD).*†

Figure 1: Number of repetitions in each set with 1-, 3-, 5-minute rest interval for upper body exercise. Values are expressed in repetitions maximal (A) bench press, (B) machine chest fly, (C) leg press, (D) leg extension. *Significant difference to set 1; †Significant difference to set 2; §significant difference to set 3; |Significant difference to set 4; ‡Significant difference to 1-minute rest interval (p ≤ 0.05). #Significant difference to 3-minute rest interval (p ≤ 0.05).

The ESs were calculated using the repetition number of the first set as the pretest score, the repetition numbers of the second through fifth sets as the posttest scores, and the SD of the first set as the pretest SD. The ES data demonstrated large magnitudes of repetition reductions in all exercises and rest conditions, with the exception of the second set for the BP and LP with 3-minute rest and in the MCF and LE with 5-minute rest. The magnitude of reductions increased over successive sets for all exercises in all rest interval conditions. For all exercises, the magnitudes of reductions were larger for the 1-minute rest condition across sets. Generally, the multijoint exercises (BP and LP) presented larger magnitudes of repetition declines over successive sets vs. the single-joint exercises (MCF and LE) (Table 2).

Table 2: Effect size from the second set of each exercise with 1-, 3-, 5-minute rest intervals.*

Significant increases in RPE were evident over successive sets for both the multi and single-joint exercises, with significantly greater values for the 1-minute condition. With the exception of the LP exercise, the RPE values were significantly greater after the fourth and fifth sets for the 1- vs. 5-minute rest condition. Significant differences were also evident between the 1- and 3-minute rest conditions after the fourth or fifth sets for the MCF and LE exercises (see Table 3).

Table 3: Rating of perceived exertion in each set and exercise for 1-, 3-, 5-minute rest intervals (median).*

Discussion

The key finding of this study was that both multi and single-joint exercises exhibited similar repetition performance patterns and RPE, independent of the rest interval length between sets. Additionally, shorter rest intervals (i.e., 1 minute) resulted in greater declines in the number of repetitions completed and higher RPE scores for all exercises. These findings are divergent from recent rest interval recommendations (¹), in which 2–3 minutes between sets was recommended for multijoint exercises and 1 to 2 minutes for single-joint exercises.

To our knowledge, this is the first study to directly compare repetition performance for multi and single-joint exercises that used the same prime movers. Our data indicate that the multi and single-joint exercises that used the pectorals (e.g., BP and MCF) and quadriceps (LP and LE) presented similar declines in the repetitions per set and consequently the total repetitions completed independent of whether 1, 3, or 5-minutes rest was instituted between sets. Thus, the generalized message of this study is that if a higher training volume (via greater repetitions with a given load) is desired, then longer rest interval lengths (i.e., 3–5 minutes) between sets should be adopted regardless of the type of exercise (i.e., multi or single-joint exercises).

Previous studies that compared different rest interval lengths for single-joint exercises are scarce, whereas several experiments have focused on multijoint exercises (^10,16-18). Specifically, Willardson and Burkett (¹⁶) compared the effects of 3 different rest intervals on BP and back squat repetitions; 4 sets of BP and back squat were performed with an 8RM load and either 1-, 2-, or 5-minute rest intervals between sets. The results demonstrated that for the back squat exercise, greater total repetitions were completed for the 5-minute condition vs. the 1- and 2-minute conditions; there was no significant difference between the 1- and 2-minute conditions. For the BP, there was a positive linear relationship between the rest interval and total repetitions; the longer the rest interval, the greater the total repetitions completed. These results were consistent with this study for the BP, in which the 1-minute rest interval demonstrated significantly fewer total repetitions vs. the 5-minute condition.

With relevance to this study, the prime movers for the BP and MCF are the pectorals and for the LP and LE, the quadriceps. The secondary movers for the BP are the triceps brachii and anterior deltoid and for the LP, the gluteals and hamstrings. The findings of this study indicate that the addition of secondary movers for the BP and LP did not allow for completion of additional repetitions or negate the decline in the repetitions over successive sets, independent of the rest condition. This was a surprising finding, given the potential for load sharing among multiple muscle groups during fatiguing muscle actions. The secondary movers used for the BP and LP could not produce sufficient force for continued repetitions once the prime movers had fatigued; thus, the total repetitions completed and pattern of decline in repetitions per set were similar for the multi and single-joint exercises. However, these findings are only relevant to the exercises examined (i.e., BP, MCF, LP, and LE) and additional research is necessary to validate these findings for other multi and single-joint exercises (e.g., supinated pull-up and biceps curl).

Recent studies demonstrated declines in repetition performance with successive exercises for the lower and upper body (^9,13). Senna et al. (¹³) compared repetition performance during 4 sessions that included 3 exercises for the lower body (i.e., LP, LE, and leg curl) and 3 exercises for the upper body (i.e., BP, MCF, and triceps pushdown) with either 2 or 5-minute rest intervals between sets. Exercises in all sessions were performed for 3 sets with a 10RM load. For the 2-minute sessions, most exercises presented declines in repetitions for the second set compared to the first set (excluding the MCF) and for the third set compared to the first and second sets (excluding the LE). For the 5-minute sessions, 3 of the 6 exercises presented declines in repetitions for the third set compared to the first set (LP, leg curl, and triceps pushdown) and 2 of the 6 exercises for the third set compared to the second set (leg curl and triceps pushdown). The total repetitions completed were significantly less for 2-minute sessions compared to the 5-minute sessions (¹³). The study by Senna et al. differed from the current study, in which the accumulated fatigue from the initial exercises may have impacted performance for subsequent exercises. However, consistent with this study, exercises involving both lower and upper body muscle groups presented similar performance patterns to different rest interval lengths.

Currently, the RPE is used to verify the intensity of resistance exercise sets (^5-8). This study demonstrated significant increases in RPE with successive sets for both the multi and single-joint exercises, with significantly greater values for the 1-minute condition. The 1-minute condition may emphasize anaerobic glycolysis to a greater extent to compensate incomplete resynthesis of phosphocreatine. The greater reliance on anaerobic glycolysis is associated with the accumulation of H⁺, which lowers the pH of intracellular fluid. The resulting afferent feedback from muscle chemoreceptors and nociceptors may increase the perception of exertion as the central nervous system increases pulmonary ventilation and motor unit recruitment.

Practical Applications

This study adds to the growing body of knowledge concerning the importance of specifically programming the rest interval between sets. Our results suggest that the rest interval between sets directly affects the repetitions completed over successive sets and the RPE. The results of this study can be used by the coach to improve the efficiency and effectiveness of resistance training sessions. The results indicated that regardless of whether the exercise is multi or single joint, the additional rest time between sets yielded additional repetitions. Furthermore, for efficiency sake, the 3-minute condition was as good as the 5-minute condition in the case of the free weight BP. For the other exercises (i.e., MCF, LP, and LE), the 5-minute condition produced superior performance.

These results are applicable and limited to the specific exercises, rest intervals, and load examined. When maximizing strength is the goal, the ability to perform greater repetitions with a given load may enhance adaptational processes, leading to greater gains. Therefore, while accounting for the aforementioned limitations, coaches can take the information from this study and prescribe rest intervals between sets accordingly. From a practical perspective, if 5-minute rest intervals are instituted between sets of the same exercise, a suggestion to avoid wasting time would be to perform exercises in complexes, alternating between movements that involve agonist and antagonist muscle groups. However, this suggestion is only speculative in terms of preserving repetition performance for the agonist movement and should be further examined under controlled conditions.