Neither repetition duration, nor number of muscle actions affect strength increases, body composition, muscle size or fasted blood glucose in trained males and females.

A key variable within resistance training (RT) is that of repetition duration; the time (seconds; s) taken to perform the concentric and eccentric muscle actions of a repetition. Research has produced equivocal results with regards to strength and muscle mass increases whilst many studies have created parity in the number of repetitions though there has been a disparity in load used and time-under-load (TUL). The purpose of this study was to compare load, and TUL matched groups performing resistance exercise using differing repetition durations. Fifty-nine male and female participants were randomised in to 3 groups; 2s:4s (n=18), 10s:10s (n=20) and a group which performed a 30s eccentric, 30s concentric and 30s eccentric muscle actions (e.g. 1.5 repetitions; n=21). Participants were supervised in 1-on-1 RT sessions 2 d.wk-1 for 10 weeks. Outcomes were 10-repetition maximum (RM) and predicted 1RM for chest press, leg press and pull-down exercises, as well as body composition, upper arm and thigh muscle mass and fasted blood glucose. Analyses revealed significant increases in strength for all exercises but no between-group differences, and no statistically significant time course changes for the other variables. Repetition duration does not affect the increases in strength in trained participants where exercise is performed to momentary failure. Since time constraints and perceived difficulty are often cited barriers to exercise, it is important to recognise that the low-volume (single-set), machine-based protocol employed herein produced worthwhile strength increases in trained participants.