Muscle Function and Aging Dain LaRoche, Ph.D

JOHNSON, VERMONT STATE COLLEGE JOHNSON Introduction Muscle force and power production decrease with aging Locomotion, fall risk, activities of daily living, and independence Is the loss of muscle function associated with aging process or physical inactivity?

JOHNSON, VERMONT STATE COLLEGE JOHNSON Decrease in muscle function due to: – –Loss of muscle mass and quality – –Decrease in type II (fast twitch) fibers – –Inability to recruit motor units – –Decreased motor unit firing rate May affect rate of force development (power) in addition to total force Muscle Function

Motor Unit

JOHNSON, VERMONT STATE COLLEGE JOHNSON Muscle Quantity and Quality

JOHNSON, VERMONT STATE COLLEGE JOHNSON Purpose To examine the effects of age and physical activity on the determinants of muscle power

JOHNSON, VERMONT STATE COLLEGE JOHNSON Methods Able-bodied, independent women aged years old Historical physical activity questionnaire and muscle function test will be administered Cybex Dynamometer and Biopac Data Acquisition System – –Force – –Electromyography (EMG)

JOHNSON, VERMONT STATE COLLEGE JOHNSON Cybex Dynamometer

JOHNSON, VERMONT STATE COLLEGE JOHNSON Procedure Participants will be secured to the dynamometer for knee extension Surface EMG electrodes will be placed over the vastus lateralis muscle Subjects will maximally extend the knee as quickly as possible following a visual stimulus. EMG will be recorded with Biopac PRO v3.6.7

JOHNSON, VERMONT STATE COLLEGE JOHNSON Visual Stimulus

JOHNSON, VERMONT STATE COLLEGE JOHNSON Integrated EMG Force Stimulus Rate of Force Development Time to Peak PMT EMD

JOHNSON, VERMONT STATE COLLEGE JOHNSON Measures Premotor time – –calculated by determining the time from initiation of the stimulus to detection of EMG Electromechanical delay – –determined by calculating the time from the onset of the EMG until the detection of force Time to peak force – –determined by calculating the time from the onset of the stimulus until peak force

JOHNSON, VERMONT STATE COLLEGE JOHNSON Measures Peak force – –the highest force measured Rate of force development – –slope of the force versus time line Onset EMG – –comparison of onset EMG to peak force EMG

JOHNSON, VERMONT STATE COLLEGE JOHNSON

JOHNSON, VERMONT STATE COLLEGE JOHNSON Expected Results Greater in Inactive: – –Pre-motor time – –Electromechanical Delay – –Time to Peak Lower in Inactive: – –Rate of Force Development – –Onset to Peak EMG Ratio Lower Power Output in Inactive!

JOHNSON, VERMONT STATE COLLEGE JOHNSON Next Steps Subject recruitment and data collection Power training intervention Muscle function and aging

JOHNSON, VERMONT STATE COLLEGE JOHNSON Thank You! Johnson State College