Spinal Network Adaptability for the Control of Steady Contractions in Men and Women

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As we age, our functional movement declines. However, this decline is more pronounced in women than in men. Over the next 5 years, studies will be conducted where functional movement is modeled through the task of lifting and lowering a cup for drinking and control is measured through variability in force or acceleration of the elbow flexors in young (18-25 y) and old (>75 y) men and women. Spinal inputs that modulate motoneuron output in the biceps brachii will be quantified in the evaluation of force control in the functional movement. The biceps brachii muscle, through distinct anatomical and physiological compartments of the short and long head is ideal for studying how small changes in motoneuron activity impacts force production, especially forearm control that is central to functional movement. Experiments will use surface and indwelling electromyography (EMG) to measure the activity of specific muscles and motor units that regulate the production of steady contractions. Through a series of investigations we will be the first to quantify single motor unit activity during functional movement and how reflex feedback is integrated and alters spinal motoneuron output relevant to producing steady contractions in young and old men and women. This research will generate fundamental knowledge about spinal networks in humans that collectively contribute to motoneuron output in the regulation of functional movement. This research is significant as determination of spinal integration relative to motoneuron output is necessary for understanding the plasticity in the neuromuscular system that contributes to sex-specific age-related decline of functional movement. Consistent with prior investigations, this research program will result in advanced training for approximately 20 highly qualified personnel enabling technical skill development in neurophysiology applicable to scientific discovery in basic human movement science.