Motor unit recruitment patterns in traditional strength loading and peak average power loading protocols

Abstract

Peak average power (PAP) and traditional strength (TS) loading methods demonstrate similar strength responses. Motor unit recruitment strategies of PAP loading have yet to be explained. The purpose of this study was to 1) understand if isotonic and isokinetic contractions have similar responses, and 2) compare PAP and TS loading methods. A total of 30 (15M, 15F) healthy participants (23.1 ± 3.0 yrs.; 173.3 ± 7.9 cm; 76.6 ± 13.6 kg) were recruited. There were three testing sessions: baseline and two experimental data collection sessions (isokinetic contractions (isokinetic dynamometer) and isotonic contractions (back squats)). For the isokinetic condition, TS loading used a speed of 30 deg/s (85% of maximal torque capacity), while PAP loading used a speed of 120 deg/s (100% maximal torque capacity). For the isotonic contraction condition, TS loading used a load of 85% 1-RM, while PAP loading used a load of 67% 1-RM. Muscle activity was measured using high-density electromyography (EMG). Spatial EMG parameters were found not to be significantly different between the two contraction conditions. TS and PAP loading methods do not differ in their motor unit recruitment patterns. Therefore, PAP loading may be a viable method to reduce the strain on the musculoskeletal system, while still stimulating the high threshold motor units.