Poyhonen T (2002) Neuromuscular function during knee exercises in water

The present series of studies examined neuromuscular function during knee exercise inwater and training responses of an aquatic exercise program. Emphasis was placed onthe quantification of water resistance, the drag. Subjects who participated in this seriesof studies were 25-35-year-old healthy women and men. Neuromuscular function wasexamined using electromyography (EMG), force and reflex sensitivity measurementsin the isometric condition on land and in water. EMG and angular velocity weremeasured during dynamic knee extension-flexion in still and flowing water. The dragforces acting on the leg and foot model were measured in the barefoot condition andwith a large resistance boot. The calculated coefficients of drag were then utilised tofurther calculate the drag forces for the human subjects. Finally, the effects of 10 weeksof aquatic resistance training on isometric and isokinetic torque, EMGs and leanmuscle mass (LCSA) were investigated. The results showed lower values for EMGactivity and for the EMG/force ratio in water than on land. The same trend wasobserved for the H- and tendon reflex responses. The EMG patterns in the repeatedknee extension-flexion performed in the flowing water demonstrated an early decreasein the concentric activation of the agonists with simultaneous eccentric activation of theantagonists. This indicates stretch-shortening cycle type of exercise whereas the singletrial exercises seemed to be purely concentric. The drag forces calculated for the humansubjects in knee extension-flexion showed significantly higher values when using theresistance boot than in the barefoot condition with values reaching 210 ± 46 N in menand 146 ± 30 N in women. The forces measured on land were significantly higher thanthe drag forces in water. Ten weeks of aquatic training resulted in a significantimprovement (8-13%) in maximal torque, and this was accompanied with significantincreases of 19-27% in the EMGs and 4-6% in the LCSA of the knee extensors andflexors. The results indicated an impairment of neuromuscular function in water,which is possibly due to hydrostatic pressure and the reduced gravity conditions. Theresults also indicated that by considering the principles of hydrodynamics, and byusing additional devices, water resistance can produce a sufficient exercise stimulus tocause positive changes in the neuromuscular system. This will add to the body ofknowledge concerning the nature of aquatic exercises and the design of progressiveaquatic exercise programs used in rehabilitation and conditioning in water. Key words: hydrodynamic drag, water immersion, electromyography, reflex sensitivity, aquatic training, muscle torque, muscle mass

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