Supraspinal And Muscular Efficiency During Isokinetic Knee Extensions At Three Different Velocities

Abstract

Increases in cerebral oxygenation (Cox) are associated with increases in neuronal activation by means of a neurovascular coupling mechanism, while declines in muscle oxygenation (Mox) imply increases in muscle oxygen extraction. PURPOSE: To compare the changes in supraspinal (SSeff) and muscular (MUeff) efficiency during three different velocities of unilateral knee extensions via Near infrared spectroscopy (NIRS). METHODS: Eleven (seven males and four females aged (mean±SD) 23.5 ±3.3 years), consented to complete a protocol of 15 unilateral isokinetic contractions at 150, 300 and 450°·sec-1 in a single testing session, with 4 mins recovery between trials. NIRS was used to examine the changes in Cox and Mox from the left prefrontal lobe and right vastus lateralis respectively. SSeff and MUeff were calculated as the ratios between average torque and the increase in Cox and decline in Mox respectively, from resting baseline values. Repeated measures ANOVA were used to compare the values among the three trials. RESULTS: The power outputs were consistent with the force-velocity curve for muscle contractions. Average torque, Cox and Mox were significantly higher (P <.05) at 150°·sec-1 compared to 300 and 450°·sec-1. This implies that the greater torque at 150°·sec-1 was accompanied by greater neuronal activation and higher muscle oxygen extraction. However, there were no significant differences (P >.05) in SSeff and MUeff among the three contraction velocities. CONCLUSIONS: Isokinetic muscle contractions which result in differing power outputs at different velocities are closely regulated by neuronal and muscular factors such that the overall efficiency remains the same.TABLE