Muscle sympathetic nerve activity during intermittent handgrip exercise

Aim. This study evaluated whether central command plays an important role in activating muscle sympathetic nerve activity (MSNA) during short-term maximal handgrip contractions. Methods. The increase in MSNA was examined while influence of minimizing for other factors such as mechanoreflex, metaboreflex and fatigue during repetitive exercise in seven 19- to 26-year-old participants. Maximal voluntary handgrips (15-s contraction with a 45-s relaxation) were performed 10 times with a 15-s pause between alternate hands. MSNA was recorded from the tibial nerve analyzed using the burst frequency (BF) and total sympathetic nerve activity. Results: The BF increased with the first unit, from 14.9 +/- 1.8 bursts-min(-1) at baseline to 27.7 +/- 3.4 bursts.min(-1) during contraction. The increase in the MSNA during contractions remained unchanged throughout the repetitions. The BF declined to baseline during the relaxation periods. The peak grip force decreased from 333 +/- 25 N for the first grip to 216 +/- 20 N for the last contraction. The MSAN increase remained constant despite a possible reduction in mechanoreflex during exercise as indicated from decreased maximal handgrip force. Conclusion. We suggested that the MSNA response was induced mainly by central command during short-term maximal handgrip contraction without metaboreflex influence and attenuated mechanoreflex input.