Muscle sympathetic nerve activity during intermittent handgrip exercise

This study evaluated whether central command plays an important role in activating muscle sympathetic nerve activity (MSNA) during short-term maximal handgrip contractions.

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.

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.

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.