Isokinetic trunk extension and flexion strength-endurance relationships.

This study examined the relationship between sagittal plane isokinetic trunk extension and flexion strength and endurance using three isokinetic velocities (60, 120, and 180° s(-1)). Healthy male subjects with no history of low back problems performed 25 consecutive repetitions of a 100° trunk extension-flexion task with encouragement to execute each repetition with maximum effort. Between each isokinetic velocity, 5 min of rest were provided. The traditional isokinetic variables of peak torque and work for trunk extension and flexion were extracted from the torque-position curves and fatigue profiles were generated with linear regression using the mean values of peak torque and work from repetitions 2-4, 7-9, 12-14, 17-19 and 22-24. The linear regression analysis defined the relationship between fatigue and the number of repetitions. The rate of fatigue (given by the slope of the regression equation) and the magnitude of the fatigue was maximum in the 60° condition. The fatigue rate and the magnitude were both related to the absolute strength given by the maximum work output. The trunk flexors were observed to be more susceptible to fatigue than the trunk extensors.