Shouting Strengthens Maximal Voluntary Force with Pupillary Dilation
Abstract Previous research has demonstrated that human maximal voluntary force is generally limited by neural inhibition. Indeed, producing a shout during maximal exertion efforts enhances the force levels of maximum voluntary contractions. However, the mechanisms underlying this enhancing effect of force production remain unknown. We investigated the influence of a shout on the pupil-linked neuromodulatory system state by examining pupil size. We also examined its effect on the motor system state by examining motor evoked potentials in response to transcranial magnetic stimulation applied over the contralateral primary motor cortex, and by evaluating the handgrip maximal voluntary force. Analysis showed that a shout significantly increased the handgrip maximal voluntary force, followed by an increase in pupil size and a reduction of the cortical silent period. Our results indicate that a shout can increase handgrip maximal voluntary force through the enhancement of motor cortical excitability, possibly via the enhancement of noradrenergic system activity. This study provides evidence that the muscular force-enhancing effect of a shout during maximal force exertion is related to both the motor system state and the pupil-linked neuromodulatory system state.