Heart rate responses at onset of contraction.

We tested the hypothesis that the initial heart rate (HR) response at the onset of maximal handgrip contraction is altered after training. 17 volunteers (nine trained and eight controls) performed ten intermittent static handgrip contractions with maximal effort, alternating between 15-s contractions and 15-s pauses. High-intensity static handgrip training was performed using the nondominant arm alone for 4 weeks. Handgrip force (HGF) and HR were analyzed for the initial 7 s of every static handgrip exercise. Peak HR (pre-training: 94.5 +/- 12.8 beats/min; post-training: 89.7 +/- 10.2 beats/min, p < 0.05) decreased. However, the magnitude of HR change at the onset of contraction remained constant (pre-training: 23.0 +/- 7.7 beats/min; post-training: 25.7 +/- 6.5 beats/min, p = 0.0767), while the HR responses in the subsequent bouts increased after training (p < 0.001). The resting HR decreased (pre-training: 71.5 +/- 9.3 beats/min; post-training 64.1 +/- 5.7 beats/min, p < 0.05). Maximal HGF increased by 11.1 % in trained arms and by 8.7 % in untrained arms, although an increase in maximal forearm girth was only observed in the trained arm (2.0 %, p < 0.0001). Although high-intensity training modulated the abrupt HR responses, the magnitude of the response remained unchanged at the onset of maximal forearm contraction and the resting HR significantly decreased.