Rapid movement kinematic and electromyographic control characteristics in males and females.

Maximally fast, self-terminated elbow flexion movements were performed by 10 male and 10 female college-aged subjects to assess potential gender-related differences in kinematics and the triphasic electromyographic (EMG) pattern. The subjects were instructed to move their forearms as fast as possible through 90 degrees of elbow flexion range of motion and stop as sharply as possible at the terminal point. An electromagnet, set to 0, 40, and 70% of each subject's maximal isometric torque, provided resistance to movement initiation and resulted in quick release movements. Surface EMG was collected from the biceps b. and triceps b. muscles. Results indicated that the males had faster movements and accelerations under all conditions. EMG records indicated that the males had faster rates of EMG rise, particularly in the triceps b., and more tightly coupled reciprocal activation. The quick release afforded faster accelerations for both groups, yet only the males moved faster throughout the full range of motion. Following the quick release, the males differed from the females by increasing the triceps b. EMG amplitude. Hence, the males were able to shorten movement time in quick release movements by increasing triceps b. activation and, thus, braking ability. These results suggest that the females were more neurally constrained than the males with respect to rapid EMG activation of the triceps b., resulting in limits in the braking process.

Voluntary and reflex responses to fatigue with stretch-shortening exercise.

The effects of 50 depth-vertical jumps (DJ) on counter-movement vertical jump (CMJ), squat jump (SJ), and DJ, isometric knee extension force (MVC), and patellar tendon response were examined in 12 men. There was no reduction in the height of the 50 DJs, but the contact time lengthened by 16%. Height of CMJ and DJ did not change after the 50 DJs, but the activity duration of the leg muscles averaged 13.2% longer. Conversely, height of SJ declined by 11.3%. MVC decreased by 20.1%. No changes occurred in reflex latency and peak-to-peak duration of the compound muscle action potential (AP), but reflex time, AP duration, and AP amplitude increased by 6.4, 6.1, and 23.3%. Thus, subjects compensated for the loss of voluntary force by lengthening the activity duration of the prime movers, potentiating muscle fiber action potentials, and/or enhancing muscle spindle sensitivity.