Objectives: To examine maximal strength and fatigability of the knee extensors, and mechanomyographic amplitude (MMGRMS)-force relationships of the vastus lateralis (VL) during repetitive muscle actions for 5 aerobically-(AT), 5 resistance-trained-(RT), and 5 sedentary (SED) individuals.
Methods: Participants performed maximal voluntary contractions before (MVCPRE) and after (MVCPOST) attempting 20 isometric trapezoidal muscle actions at 50% MVCPRE. MMG was recorded from the VL. b terms (slopes) were calculated from the natural log-transformed MMGRMS-force relationships for each participant (increasing and decreasing segments). MMGRMS was averaged during steady force.
Results: RT had greater MVCPRE (P<0.001) and MVCPOST (P=0.001-0.004) than AT and SED. Only AT completed 20 muscle actions and exhibited no decrease in MVCPOST (P=0.149). The b terms were greater for RT than AT during the increasing segment of the first contraction (P=0.001) and decreasing segment of the last contraction (P=0.033). The b terms were also greater for RT (P=0.006) during the increasing than decreasing segment for the first contraction. MMGRMS during steady force was greater during the last contraction when collapsed across training status (P=0.021).
Conclusion: Knee extensor MVC and fatigability, and motor unit control strategies for the VL during a series of repetitive contractions were influenced by chronic training status.
Keywords: Isometric Trapezoidal Muscle Action; Log-Transform Model; Mechanomyography; Motor Unit Control Strategies; Vastus Lateralis.