Time of day effect on isokinetic peak torque during knee flexion and extension

BACKGROUND: The effects of circadian rhythms on aerobic exercise have been well documented, but little research has been conducted during isokinetic exercise. OBJECTIVE: The purpose of this study was to examine how isokinetic peak torque of the knee extensors changes throughout the day. METHODS: Twenty-five college-aged recreational athletes (14 females, 11 males) completed one familiarization and three experimental sessions on a Cybex NORM isokinetic dynamometer, with start times of 08:00-09:00, 13:00-14:00, and 18:00-19:00. Each session began with a five-minute warmup on a cycle ergometer and three sets of four submaximal concentric discrete knee extensions at 60, 180 and 300°/s, with knee flexion held constant at 300°/s and a one minute rest between velocity sets. This was followed by four maximal concentric discrete knee extensions with the same parameters as the warmup. Peak torque was recorded for each velocity. Data were analyzed using a two-way 3 (time) × 3 (velocity) repeated measures ANOVA (α ≤ 0.05). RESULTS: There were no significant differences in peak torque by time of day at any velocity among females (n= 14), males (n= 11), or the entire group (n= 25). CONCLUSIONS: When measuring knee extension peak torque in these college-aged subjects, time of day was not a factor.