| Abstract: | The purpose ofthis study was to determine the effects of concentric (Con) andeccentric (Ecc) muscle actions on leg muscle sympathetic nerve activity(MSNA). Two protocols were utilized. In protocol1, eight subjects performed Con and Ecc arm curls for 2 min, with a resistance representing 50% of one-repetition maximum forCon curls. Heart rate (HR) and mean arterial pressure (MAP) weregreater (P < 0.05) during Con thanduring Ecc curls. Similarly, the MSNA was greater(P < 0.05) during Con than during Ecc curls. In protocol 2, eightdifferent subjects performed Con and Ecc arm curls to fatigue, followedby postexercise muscle ischemia, by using the same resistanceas in protocol 1. Endurance time wassignificantly greater for Ecc than for Con curls. The increase in HR,MAP, and MSNA was greater (P < 0.05)during Con than during Ecc curls. However, when the data werenormalized as a function of endurance time, the differences in HR, MAP,and MSNA between Con and Ecc curls were no longer present. HR, MAP, andMSNA responses during postexercise muscle ischemia were similar for Con and Ecc curls. Con curls elicited greater increase(P < 0.05) in blood lactateconcentration than did Ecc curls. In summary, Con actions contributesignificantly more to the increase in cardiovascular and MSNA responsesduring brief, submaximal exercise than do Ecc actions. However, whenperformed to a similar level of effort (i.e., fatigue), Con and Eccmuscle actions elicit similar cardiovascular and MSNA responses. Theseresults indicate that the increase in MSNA during a typical bout ofsubmaximal dynamic exercise is primarily mediated by the musclemetaboreflex, which is stimulated by metabolites produced predominantlyduring Con muscle action. |
