Effects of a Thorstensson fatiguing protocol on isometric and isokinetic performance

OBJECTIVE: Having participants perform 50 maximal isokinetic contractions, as introduced by Thorstensson and Karlsson (1976), is to this day one of the most commonly used fatigue protocols. Purpose: To determine to what extent a Thorstensson fatiguing protocol affects isokinetic and isometric performance characteristics. METHODS: Twenty-five college-aged men performed an isokinetic fatigue protocol consisting of 50 maximal elbow flexions at a moderate speed (180 degrees(.)s(-1)). Pre- and post-tests were used to calculate fatigue indices (FI%) for the following variables: isometric and isokinetic peak torque (PT), isometric rate of torque development (RTD), and maximum acceleration (ACC(max)). RESULTS: Each of the four dependent variables significantly decreased with fatigue (each demonstrated p < 0.001), but not of the same magnitude. Isometric PT FI ( 18.7%) was significantly less than isokinetic PT FI ( 45.1%, <= 6 0.001) and ACC max FI ( 26.3%) was significantly less than isometric RTD FI ( 54.9%, <= 6 0.001). There was a significant positive relationship between isometric and isokinetic PT FI% (r = 0.60, p < 0.002) as well as between isometric PT FI% and RTD FI% (r = 0.40, p < 0.046). There was no significant relationship observed between RTD FI% and ACC (max) FI% nor between isokinetic PT FI% and ACC (max) FI%. CONCLUSIONS: This investigation observed different patterns of response in maximal strength between isometric and isokinetic assessments following a isokinetic fatigue protocol. Additionally, the ability to rapidly generate strength and velocity had significantly different responses to fatigue between isometric and dynamic assessments. Due to these different responses, we recommend that assessments of fatigue at least include the same testing modality as the modality of the fatigue protocol.

Automated summary

The purpose of this study was to determine the extent to which a Thorstensson fatigue protocol affects isokinetic and isometric performance characteristics. The results showed that the peak torque, rate of torque development, and maximum acceleration significantly decreased after performing isokinetic contractions, but to different magnitudes. There was a significant positive relationship between isometric and isokinetic peak torque fatigue indices, as well as between isometric peak torque fatigue index and rate of torque development fatigue index. However, no significant relationship was observed between rate of torque development fatigue index and maximum acceleration fatigue index, or between isokinetic peak torque fatigue index and maximum acceleration fatigue index.