The influence of chronic training status on the mechanical behavior of the vastus lateralis during repetitive trapezoidal contractions

OBJECTIVES: To examine maximal strength and fatigability of the knee extensors, and mechanomyographic amplitude (MMG(RMS))–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 (MVC(PRE)) and after (MVC(POST)) attempting 20 isometric trapezoidal muscle actions at 50% MVC(PRE). MMG was recorded from the VL. b terms (slopes) were calculated from the natural log-transformed MMG(RMS)-force relationships for each participant (increasing and decreasing segments). MMG(RMS) was averaged during steady force. RESULTS: RT had greater MVC(PRE) (P<0.001) and MVC(POST) (P=0.001–0.004) than AT and SED. Only AT completed 20 muscle actions and exhibited no decrease in MVC(POST) (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. MMG(RMS) 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.