Changes in electromyogram during upper limb muscle contraction induced by resistive loaded breathing in humans.

Expiratory only resistive loaded breathing (RL) reduces high energy electromyogram (EMG) power (EH) during an isometric contraction of a leg extensor muscle, but not an arm flexor. An interaction between afferent activity during expiratory RL and inspiratory non-loaded phases of breathing, which the contraction spanned, could have accounted for the reduced EH in these long contractions. Therefore this study tested the hypothesis that brief arm extensor muscle contractions (70% of maximal force), performed during a single phase of expiratory RL, would also exhibit reduced EH. Surprisingly, EH in triceps, but not biceps brachii was reduced significantly when the contraction was performed during inspiratory RL rather than expiratory RL. The results suggest that either (a) short and prolonged contractions or (b) motor drive to arm and leg extensors are affected differently by RL.