Postural control when standing on an unstable surface under psychological pressure: Evaluation from lower limb muscular activity and center of pressure

Abstract

The effects 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.