Terry J. Housh

A method for estimating physical working capacity at the fatigue threshold (PWCFT).

Presently available tests of physical working capacity (PWC) such as [Vdot]O2max and critical power may not be appropriate for unfit subjects because they require maximal or supramaximal workloads. Therefore, the purpose of this study was to evaluate a submaximal discontinuous incremental bicycle ergometer test (PWCFT) with an end point (fatigue threshold) determined by recording electromyographic (EMG) fatigue curves in the quadriceps muscle. The fatigue threshold was defined as the lowest workload producing a slope of the EMG voltage-time relation that was significantly different from zero slope at p<0.05 (single tail). The test-re-test reproducibility of PWCFT (n=17 subjects) was found to be r = 0.947, with no significant difference between trials. Thirty-two healthy male subjects aged 18-29 (mean 23-4 ± 31 years) whose fitness levels ranged from highly trained to untrained sedentary level were tested for PWCFT, lactate threshold (OBLA), percentage heart rate range at PWCFT (%HRR), and heart rate-workl...

Co-Activation, Estimated Anterior and Posterior Cruciate Ligament Forces, and Motor Unit Activation Strategies during the Time Course of Fatigue

This study aimed to combine co-activation as well as anterior and posterior cruciate ligament force estimations with the motor unit activation strategies employed by the primary muscles that are involved in the movement at the knee joint. Fourteen male subject performed 25 maximal concentric isokinetic leg extension muscle actions at 120 s−1. Electromyographic and mechanomyographic signals from the vastus lateralis and bicep femoris, as well as force, were used to measure co-activation, and estimated anterior and posterior ligament forces during the time course of fatigue. There were decreases in quadriceps force and increases in hamstring force during the 25 leg extensions. The posterior cruciate ligament force was greater than the anterior cruciate ligament force during each leg extension. Both the posterior and anterior cruciate ligament forces decreased during the 25 leg extensions. Each muscle indicated unique neuromuscular responses, which may explain the decreases in quadriceps force and increases in the hamstring force. The combination of anterior and posterior cruciate ligament force estimation and motor unit activation strategies helped to provide a better understanding of the fatigue-related mechanism that was utilized to avoid injury and increase or maintain joint stability during the time course of fatigue.