Author(s): BOGDANIS, G., VERVERIS, A., TSOUKOS, A., Institution: NATIONAL & KAPODISTRIAN UNIVERSITY OF ATHENS, Country: GREECE, Abstract-ID: 636

INTRODUCTION:
Cluster sets incorporate brief intra-set rest intervals that increase repetition performance and reduce metabolic stress [1]. However, most studies have equated total repetitions between conditions, and it remains unclear whether these advantages persist when exercises are performed to momentary failure. This study compared a continuous set and a cluster set with 10 s intra-set rest performed to failure on repetition number, time under tension (TUT), heart rate (HR), and blood lactate (BL) during bench press and half-squat exercise.
METHODS:
Ten resistance-trained men (age: 24.4 ±4.2 years; height: 174.0±6.0 cm; body mass: 76.3±7.9 kg; body fat: 10.1±4.0%) completed one-repetition maximum (1RM) testing in Smith machine bench press and half-squat. Participants performed two conditions at 85±1% 1RM (bench press) and 84±3% 1RM ( half-squat): a continuous set to momentary failure (CON), and a cluster-set configuration (CS) in which three repetitions were performed followed by a 10 s intra-set rest interval, repeated until failure. Condition order was randomized and counterbalanced; exercise order was fixed (bench press followed by half-squat after 20 min rest). In both exercises, repetitions were performed with maximal intended concentric velocity and without an imposed pause at the lower position; the bar contacted the chest during the bench press and the safety pins at ~85° knee flexion during the half-squat, with the eccentric phase immediately followed by concentric execution. BL was measured before and again one and three minutes after exercise. HR was continuously recorded. Data were analyzed using repeated-measures ANOVA.
RESULTS:
Bench press 1RM was 94.0±17.7 kg (1.23±0.18 kg/kg body mass). Half-squat 1RM was almost two-fold higher (180.3±25.3.7 kg or 2.37± 0.31 kg/kg body mass). The number of repetitions to failure for bench press was similar in CS and CON (8.2±1.3 vs. 6.9±1.8; p=0.45). In contrast, half-squat repetitions were significantly greater in CS compared with CON (18.3±4.0 vs. 10.6±3.2; p < 0.001), accompanied by a 51% increase in TUT (p<0.001).BL increased similarly between conditions in the bench press, (5-6 mmol/L, p<0.001). After the half-squat, BL reached higher values (8–9 mmol/L, p<0.001) and was significantly greater in CS than CON (p<0.001). Mean HR was similar between conditions in the bench press (66±9 vs. 67±8% HRmax), but was higher in half-squat, with greater responses in CS compared with CON (83±4 vs. 77±7 % HRmax, p<0.01).
CONCLUSION:
When performed to momentary failure, cluster sets increase training volume in the half-squat but not in the bench press, indicating an exercise-specific effect under high-load conditions. Contrary to previous evidence, metabolic stress was not attenuated and was greater in CS during half-squat. The half-squat elicited greater mechanical and physiological stress than the bench press, regardless of configuration.

1. Tufano JJ, Brown LE, Haff GG. J Strength Cond Res 2017;31:848–867.