title: Effect of slow velocity isokinetic knee actions on slow and fast velocity contralateral knee action performance
Creators: name: Duffett, Colin Arthur
Publisher: name: Memorial University of Newfoundland
Year: 2020

description: Fatigue is a complex, multifactorial phenomenon that affects the neuromuscular system from the muscle fibers and neuromuscular junction to the higher planning centers in the brain and reflects interactions along the entire system. ‘Neuromuscular fatigue’ refers to the decrease in physical performance associated with an increase in the real and/or perceived difficulty of a task, regardless if the force or power can be sustained, and is present and progressing from the onset of the task that is reversible with rest. It consists of central and peripheral components such as decreases in central drive (central fatigue) or contractile responses (peripheral fatigue) and is suggested to occur at any site involved in the muscle contraction. Fatigue also has a mental component that describes an emotion suggested to act as a warning sign for maintaining physical integrity. Neuromuscular fatigue may depend on both the muscles employed and on the type of exercise from which fatigue results and are specific to the task and dependent on the mechanisms which are the most stressed during the task. Fatigue can either be localized or global, meaning it can affect the muscles exercised or the entire body system resulting in fatigue effects in non-exercised muscle groups. A growing body of research revolves around the effects of fatiguing exercise and their impact on the performance of non-exercised muscles, termed non-local muscle fatigue (NLMF). The presence of NLMF effects is conflicting, with effects seemingly dependent on many factors such as contraction intensity, fatiguing exercise volume, muscle group fatigued and tested, muscle action, and the detection method(s) used. NLMF research has many implications for rehabilitation and training purposes, as well as widening our understanding of global fatigue mechanisms. A relatively unexplored aspect of NLMF is whether the testing is velocity specific. The purpose of this study was to investigate the effects of fatigue induced by simultaneous low velocity unilateral isokinetic knee extensions and flexions on contralateral knee slow and fast velocity extensor and flexor isokinetic force and electromyography (EMG). In a randomized, repeated measures, crossover design, peak torque, EMG, and rate of perceived exertion measures were measured from the non-dominant vastus lateralis and biceps femoris before and after unilateral fatiguing protocols of the dominant knee extensors and flexors. The fatiguing protocols consisted of 4 sets of 15 maximal isokinetic knee extension and flexion contractions. In addition, a fatigue resistance test was also completed post-intervention. The current study used 16, university-aged (ages 18-30) participants (10 males and 6 females) who were resistance trained. Peak torque of the dominant (exercised) quadriceps and hamstrings decreased when tested at slow and high velocities. Peak torque of the non-dominant quadriceps and hamstrings during post-test (p=0.6 and p=0.3 respectively), or first or last repetition of repetitive fatigue test (p=0.8, p=0.06, and p=0.8, p=1.0, respectively) tested at slow velocity was not significantly different from control, demonstrating a lack of peak torque or fatigue endurance NLMF effects. In addition, there was no relative (normalized) differences in peak torque for velocity specific or fast test velocities. However, the fast velocity repetitive fatigue test resulted in a greater decrease from first to the last repetition than the slow test, as demonstrated by the fatigue index (FI), but was not significantly different from control. This study highlights that prior unilateral fatigue of the dominant quadriceps and hamstrings by repetitive slow maximal isokinetic actions did not demonstrate decreases in singular maximal peak torque or repetitive fatigue endurance in the contralateral muscles. In addition, velocity specific effects were not demonstrated in relative peak torque or relative fatigue endurance changes. There was also no observable effect on the rating of perceived exertion following control vs fatigue (4.6 vs 6.3, p>0.05), or slow vs. fast testing (5.8 vs 6.8, p>0.05) on post-repetitive test values.