EFFECT OF REST INTERVAL BETWEEN SETS IN THE MUSCLE FUNCTION DURING A SEQUENCE OF STRENGTH TRAINING EXERCISES FOR THE UPPER BODY FILIPE MATOS, 1 BRUNA FERREIRA, 2 JOANA GUEDES, 2 FRANCISCO SAAVEDRA, 1,2 VICTOR M. REIS, 1,2 AND JOSE ´ VILAC ¸A-ALVES 1,2 1 Research Center in Sports Sciences, Health Sciences and Human Development, CIDESD, Vila Real, Portugal; and 2 Sport Sciences Department, University of Tra´s-os-Montes and Alto Douro, Vila Real, Portugal ABSTRACT Matos, F, Ferreira, B, Guedes, J, Saavedra, F, Reis, VM, and Vilac ¸ a-Alves, J. Effect of rest interval between sets in the mus- cle function during a sequence of strength training exercises for the upper body. J Strength Cond Res XX(X): 000–000, 2018—The objective of this study was to observe the ideal recovery time between sets and exercises, for both chest and back, which allowed for maintaining muscle function with the initial load previously established. Sixty young men recrea- tionally trained in strength training (ST) were divided into 2 groups: (a) 30 subjects were included in the GC group (the group that performed ST for the chest) and (b) 30 subjects were included in the GB group (the group that performed ST for the back). Each group was submitted to 3 experimental sessions, performing an ST sequence with 3 sets of 8 repeti- tion maximum: GC performed a chest barbell press (CBP), an inclined CBP, and a chest butterfly; GB performed a lat pull- down, a back row, and a shoulder extension on the high pulley. The experimental sessions differed in rest time between sets performed (60, 90, and 120 seconds). For both groups in each sequence, significantly higher numbers of repetitions were observed with the rest time of 120 seconds relative to the rest time of 90 seconds (p = 0.004), 120 seconds in relation to the rest time of 60 seconds (p = 0.001), and in the rest interval of 90 seconds in relation to the rest time of 60 seconds (p , 0.0001). The results showed that 120 seconds was sufficient to maintain muscle function and perform the total number of repetitions per set. The data seem to show that for the ST methodology applied, it is not appropriate to assume that a cer- tain relative intensity will translate into a similar number of rep- etitions in different exercises, especially with shorter rest intervals such as 60 and 90 seconds. KEY WORDS rest time, number of repetitions, rest time, fatigue, exercise order INTRODUCTION S trength training (ST) is the primary form of exer- cise to obtain muscle hypertrophy. The traditional recommendations are the relative intensities of 75– 85% of 1 repetition maximum (1RM) or to alter- natively perform 8–12RM, with rest intervals between sets of 30 and 60 seconds, assuming that are the most appropriate to obtain the necessary and favorable conditions for muscle growth (4,6,20). Previous authors have proposed that rest intervals of 30–60 seconds are optimal because short rest periods augment the growth hormone (GH) response when compared with long rest periods (6,11,17). There might be higher acute elevations in GH with 30-second to 1-minute rest between sets, but this represents one variant that may or may not be associated with long-term increases in muscular hypertrophy (4,17). Other anabolic hormones such as testos- terone and insulin-like growth factor-I are not elevated with short rest intervals between sets but with larger volume training (4,17,18). For example, Rahimi (17) found that for 4 sets of squat and bench press to failure using 85% of 1RM, a rest period of 60 seconds results in greater serum GH levels and less total training volume than a rest period of 90 and 120 seconds, but the testosterone response was greater in the ST sessions with long rest periods (90–120 seconds) and higher training volumes. Strength training volume is commonly defined as the total amount of work performed and can be expressed in several ways. A popular method for quantifying ST volume is the total number of repetitions performed per exercise. How- ever, short rest periods impair physical performance during subsequent sets; increasing the relative intensity of an exercise may result in a decrease in the number of repetitions Address correspondence to Filipe Matos, filipejosematos@gmail.com. 00(00)/1–8 Journal of Strength and Conditioning Research Ó 2018 National Strength and Conditioning Association VOLUME 00 | NUMBER 00 | MONTH 2018 | 1 Copyright ª 2018 National Strength and Conditioning Association