Neuromuscular generation and control of force output in humans

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This research program has had a focus on determining key factors affecting the generation and control of muscle force in humans. By using an integrative systems level approach the primary objective is to continue to provide important information in this field that is applicable to both fundamental systems physiology and applied physiology. Core techniques permit a focus on the interrelationship between central neural drive and muscle contractile characteristics during the generation and voluntary control of movement. The human model offers several important opportunities for advancing knowledge in this area. Participants can comply with various requisite tasks that reflect normal activities that are dependent on effective muscle force generation and control in the integrated whole system. These include assessing the system at various levels from the motor cortex, spinal cord and peripheral nervous system to intrinsic properties of skeletal muscle including quantity (anatomy) and quality (physiology). Matching between neural and muscular properties allows the human body to optimize movement for a given condition, and this ongoing program is exploring this relationship and it's adaptability. Experiments involve studying acute (fatigue, potentiation) and chronic adapted states (aging, training) as models with a combination of several innovative techniques that provide comprehensive information from which an integrative understanding of the human neuromuscular and musculoskeletal systems can be gained. From several inter-related studies general foci outlined in this proposal include: 1) Control of motor unit properties (recruitment and rate coding) during dynamic (shortening/lengthening) contractions as compared with most all current understanding which has been gained from isometric (static length) contractions. 2) Using models of altered states (aging) to better understand the unique relationship between neural drive and muscle responses with a new emphasis on the neuromuscular junction assessed electrophysiologically. 3) How do short term (transient) natural changes induced by fatigue affect the relationship between neural drive and contractile function? Notable in the program is the unique combination of several minimally invasive techniques either within our laboratory or through established collaborations which allow these questions to be addressed thoroughly with current technologies. These include all aspects of motor unit electrophysiology; peripheral (electrical) activation of the neuromuscular system; measures of voluntary force or torque (isometric and dynamic); ultrasound and magnetic resonance imaging of muscle.