Control of human standing posture

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My NSERC-funded research program examines how the brain controls muscle force and movement, particularly under conditions of fatigue and postural control, through the study of motor unit behaviour. The motor unit is the means for the commands from the brain to create forces in the muscle. Maintenance of upright standing is fundamental to human mobility. Standing balance is of utmost importance to prevent the devastating consequences of falls in the aged. The calf muscles are essential for standing balance and previously all the calf muscles were thought to be activated uniformly in standing. Traditionally, muscle activation is measured with two surface electrodes or fine-wire electrodes placed in the muscle but these techniques collect information from motor units confined to a relatively small muscle region (mm to cm). We will use an innovative way of studying populations of motor units occupying different regions of the calf muscles. This is achieved by using grids of 20-24 very small electrodes (called HDS-EMG) placed over the entire muscle. Using this novel technology, we will examine whether there are important regional differences in how the muscles must react to balance disturbances. We will create balance disturbances by applying loads at the subjects' hips. Loads of varying magnitude will be applied in different directions (with and without fatiguing the calf muscles) to determine if the calf muscles are activated in specific regions based on the characteristics of the balance disturbance. Young healthy subjects will be compared to elderly subjects to determine if the regional activation serves to fine tune the postural response to the balance disturbance which may be lacking in the elderly. Finally, we will explore the relationship of activation of areas of the brain with areas of localized activity in the muscle to determine if the brain influences the pattern of muscle activation during balance disturbances. This knowledge will advance our understanding of human postural control and provide insight on falls in the elderly.