AbstractThe eŠects of psychological pressure on lower limb muscular activity and center of pressure (COP) were investigated in a standing, postural control task. Healthy male participants (N＝18) performed a balancing task by standing on a balance disk with their dominant foot. Participants were requested to stabilize their posture for 30 s (one-trial). After acquisition trials, participants performed 2 non-pressure and 2 pressure trials in counterbalanced order for a performance-contingent cash reward, or punishment. Stress responses were successfully induced as assessed by state anxiety, perceived pressure, mental eŠort, and heart rates that increased under pressure conditions. The results indicated that the rate of co-contraction between the soleus (SOL) and tibialis anterior (TA) muscles in the dominant leg increased signiˆcantly in association with an increment in the EMG amplitude of the SOL under pressure. Moreover, the COP area in pressure trials was signiˆcantly smaller than in non-pressure trials. These functional changes in postural control under pressure could have been modiˆed by internal focus of attention, aŠective states including anxiety, and movement strategies that enhance muscle and joint stiŠness in the lower limbs.

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Abstract:The purpose of the present study was to investigate the effects of psychological pressure on corticospinal excitability, the spinal reflex, lower limb muscular activity, and reaction times during a task involving dominant leg movements. Ten healthy participants performed a simple reaction time task by raising the heel of their dominant foot from a switch. After 20 practice trials, participants performed 20 non-pressure and 20 pressure trials in a counterbalanced order. Stress responses were successfully induced, as indexed by significant increases in state anxiety, mental effort, and heart rates under pressure. Significant increases in motor evoked potential (MEP) amplitude of the tibialis anterior muscle (TA) occurred under pressure. In terms of task-related EMG amplitude, the co-contraction rate between the soleus (SOL) and TA muscles significantly increased along with SOL and TA EMG amplitudes under pressure. Hoffmann reflexes for SOL and reaction times did not change under pressure. These results indicate that corticospinal excitability and leg muscle-related EMG activity increase homogeneously during lower limb movements that are performed under psychological pressure.

Abstract:The purpose of the present study was to investigate the effects of psychological pressure on corticospinal excitability, the spinal reflex, lower limb muscular activity, and reaction times during a task involving dominant leg movements. Ten healthy participants performed a simple reaction time task by raising the heel of their dominant foot from a switch. After 20 practice trials, participants performed 20 non-pressure and 20 pressure trials in a counterbalanced order. A combination of pressure manipulations, including reward and penalty by monetary incentives, was used in the pressure trials. Stress responses were successfully induced, as indexed by significant increases in state anxiety, mental effort, and heart rates under pressure. Significant increases in motor evoked potential (MEP) amplitude of the tibialis anterior muscle (TA) occurred under pressure. In terms of task-related electromyography (EMG) amplitude, the co-contraction rate between the soleus (SOL) and TA muscles significantly increased along with SOL and TA EMG amplitudes under pressure. Hoffmann reflexes for SOL and reaction times did not change under pressure. These results indicate that corticospinal excitability and leg muscle-related EMG activity increase homogeneously during lower limb movements that are performed under psychological pressure.