1.
Isokinetic and isometric muscle function of the knee extensors and flexors during simulated soccer activity: effect of exercise and dehydration.
Ali, A, Williams, C
Journal of sports sciences. 2013;(8):907-16
Abstract
This study investigated the influence of dehydration during soccer-type intermittent exercise on isokinetic and isometric muscle function. Eight soccer players performed two 90-min high-intensity intermittent shuttle-running trials without (NF) or with (FL) fluid ingestion (5 ml · kg(-1) before and 2 ml · kg(-1) every 15 min). Isokinetic and isometric strength and muscular power of knee flexors and knee extensors were measured pre-exercise, at half-time and post-exercise using isokinetic dynamometry. Sprint performance was monitored throughout the simulated-soccer exercise. Isokinetic knee strength was reduced at faster (3.13 rad · s(-1); P = 0.009) but not slower (1.05 rad · s(-1); P = 0.063) contraction speeds with exercise; however, there was no difference between FL and NF. Peak isometric strength of the knee extensors (P = 0.002) but not the knee flexors (P = 0.065) was significantly reduced with exercise with no difference between FL and NF. Average muscular power was reduced over time at both 1.05 rad · s(-1) (P = 0.01) and 3.14 rad · s(-1) (P = 0.033) but was not different between FL and NF. Mean 15-m sprint time increased with duration of exercise (P = 0.005) but was not different between FL and NF. In summary, fluid ingestion during 90 min of soccer-type exercise was unable to offset the reduction in isokinetic and isometric strength and muscular power of the knee extensors and flexors.
2.
Pre-synaptic modulation of quadriceps arthrogenic muscle inhibition.
Palmieri, RM, Weltman, A, Edwards, JE, Tom, JA, Saliba, EN, Mistry, DJ, Ingersoll, CD
Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2005;(5):370-6
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Abstract
Arthrogenic muscle inhibition (AMI) impedes rehabilitation following knee joint injury by preventing activation of the quadriceps. AMI has been attributed to neuronal reflex activity in which altered afferent input originating from the injured joint results in a diminished efferent motor drive to the quadriceps muscles. Beginning to understand the mechanisms responsible for muscle inhibition following joint injury is vital to control or eliminate this phenomenon. Therefore, the purpose of this investigation is to determine if quadriceps AMI is mediated by a presynaptic regulatory mechanism. Eight adults participated in two sessions: in one session their knee was injected with saline and in the other session it was not. The maximum Hoffmann reflex (H-reflex), M-wave, reflex activation history, plasma epinephrine, and norepinephrine were recorded at: baseline, post needle stick, post lidocaine, and 25 and 45 min post effusion. Measures for the control condition were matched to the effusion condition. The percent of the unconditioned reflex amplitude for reflex activation history and the maximum H-reflex were decreased at 25 and 45 min post effusion as compared to measures taken at baseline, post needle stick, and post lidocaine (P<0.05). No differences were noted for the maximum M-wave or plasma epinephrine and norepinephrine levels in either the effusion or noneffusion admission (P>0.05). No differences were detected at any time interval for any measure during the control admission (P>0.05). Quadriceps AMI elicited via an experimental knee joint effusion is, at least in part, mediated by a presynaptic mechanism.