4–6 Repetition Maximum (RM) and 1-RM Prediction in Free-Weight Bench Press and Smith Machine Squat Based on Body Mass in Male Athletes

Abstract Dhahbi, W, Padulo, J, Russo, L, Racil, G, Ltifi, M-A, Picerno, P, Iuliano, E, and Migliaccio, GM. Four- to 6-repetition maximum and 1-repetition maximum estimation in free-weight bench press and smith machine squat based on body mass in male athletes. J Strength Cond Res 38(8): 1366–1371, 2024—This study aimed to explore the feasibility and face validity of predicting maximum strength 1 repetition maximum (1-RM) and 4–6 RM in athletes across different sports specialties, based on the relationship between muscle strength and BM. One hundred fifteen male athletes, aged 23.63 ± 6.77 years and participating in diverse sports specialties, were included in this study. Muscle strength was assessed using the 4–6 RM and 1-RM tests in free-weight bench press (BP) and Smith machine squat (SQ) exercises, whereas BM was measured using a portable digital scale. A linear regression equation based on muscle strength and BM was performed. The 4–6 RM and 1-RM scores showed excellent intersession relative reliability (intraclass correlation coefficient (2,1) : 0.946–0.989) and absolute reliability (CV: 3.4–4.7%) in both BP and SQ exercises. In addition, the magnitude of the relationship and the coefficients used to estimate the 4–6 RM and 1RM, based on BM, differed among the subjects when they are grouped according to their sports specialties ( R 2 ranged from non-significant to 0.998). Overall, the 4–6 RM test showed a stronger correlation with BM ( R : 0.655 for SQ and R : 0.683 for BP) than the 1RM ( R : 0.552 for SQ and R : 0.629 for BP), and the general (i.e., not sport-specific) 4 to 6-RM prediction equations should be preferred over sport-specific ones because they are statistically more robust due to the larger sample size. In conclusion, the 4–6 RM can be predicted from BM with high reliability, a moderate association, and a prediction error that, when considering the 4–6 RM as a starting point for estimating of the 1RM, can be considered entirely acceptable in practical settings.