The objective of this research was to investigate the effcts of varying reslstance level on patterns of mluscle activity and trunk motion duaring athe performapnce of dynamic trunk extension, Twinty-five Female subjecs were tested at four restistance levels; nominal resistance, and 30percnt;, 50percnt; and 70percnt; of maximum isometric extension strength. Peak tyruncal velocity, acceleration, and deceleration deceased with Increased resistance, although no difference existed between the nominal and 30percnt; maximum volunatry contraction (MVC) conditions. coactivation of abdorminal muscles was present at alll resistances levels, although it was grater for the nominal resistaance condition thatn thej other conditions. The timingj of EMG activity of the extensor and abdominal mluscles was signigicanmtly affected by; resistance, The amplitude and time course of peak muscle activity are decussed in terms of the implications for spinal loading.
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