Measurement of acute dynamic anaerobic muscle fatigue using a novel Fatigue Resistance Index

A variety of isokinetic fatigue protocols have been previously reported in the literature. The purpose of this study was to examine a new protocol to objectively quantify dynamic concentric and eccentric muscle performance in individuals, or in a multiple subject group, under conditions of acute exhaustive exercise. Pre-fatigue maximal peak torque (PT) and peri-fatigue PT values were measured in unilateral dominant leg quadriceps femoris of human subjects using an isokinetic dynamometer. The protocol was based on single-velocity (90 $^{\circ}$ /s) reciprocal-mode concentric/eccentric (CON/ECC) contractions fixed at 35 repetitions per set. A novel ``Fatigue Resistance Index'' (FRI) was then calculated for each individual subject for both CON and ECC contractions. The group CON FRI( $36.5 \pm 3.9$ % maximal force) was greater than group ECC FRI( $26.9 \pm 2.7$ % force). This protocol and FRI permit comparisons between eccentric and concentric dynamic anaerobic muscle performances for a given individual subject, or for a group of subjects.