Force assessment of the stimulated arm flexors: quantification of contractile properties

The primary objective was to develop equipment and evaluate protocols for non-invasive assessment of contractile properties of human arm flexors. The research design consisted of a non-randomized control trial, with repeated measures. Data from six males and two females were gathered in a clinical research laboratory. The elbow flexor torque following motor point or direct nerve stimulation was measured in response to single pulses or short trains of electrical pulses. Length--tension relationships were determined; comparative data were obtained at the identified optimal muscle lengths. Twitch waveforms and peak torques following either type of stimulation were reproducible (within 10%). Peak torques following a 4-pulse small interpulse interval stimulation were nearly identical for motor-point activation and direct nerve stimulation (15.2+/- 6.6Nm for motor point stimulation; 14.5 +/- 6.6Nm for nerve stimulation). Average perceived pain indexes associated with 4-pulse stimuli were slightly higher following nerve stimulation (782 for nerve versus 6.23 for motor-point, n=8). A reliable methodology (motor-point stimulation) has been identified to perform stimulated force assessment of human arm flexors.