Co-Activation, Estimated Anterior and Posterior Cruciate Ligament Forces, and Motor Unit Activation Strategies during the Time Course of Fatigue

Authors

Cory M. Smith, University of Nebraska - LincolnFollow
Terry J. Housh, University of Nebraska-LincolnFollow
Ethan C. Hill, University of Nebraska-LincolnFollow
Josh L. Keller, University of Nebraska - LincolnFollow
Glen O. Johnson, University of Nebraska - Lincoln
Richard J. Schmidt, University of Nebraska - LincolnFollow

ORCID IDs

0000-0001-9581-1225

0000-0003-0756-9358

Date of this Version

2018

Citation

Sports 2018, 6, 104

Comments

© 2018 by the authors.

Open access

doi:10.3390/sports6040104

Abstract

This study aimed to combine co-activation as well as anterior and posterior cruciate ligament force estimations with the motor unit activation strategies employed by the primary muscles that are involved in the movement at the knee joint. Fourteen male subject performed 25 maximal concentric isokinetic leg extension muscle actions at 120 s^-1. Electromyographic and mechanomyographic signals from the vastus lateralis and bicep femoris, as well as force, were used to measure co-activation, and estimated anterior and posterior ligament forces during the time course of fatigue. There were decreases in quadriceps force and increases in hamstring force during the 25 leg extensions. The posterior cruciate ligament force was greater than the anterior cruciate ligament force during each leg extension. Both the posterior and anterior cruciate ligament forces decreased during the 25 leg extensions. Each muscle indicated unique neuromuscular responses, which may explain the decreases in quadriceps force and increases in the hamstring force. The combination of anterior and posterior cruciate ligament force estimation and motor unit activation strategies helped to provide a better understanding of the fatigue-related mechanism that was utilized to avoid injury and increase or maintain joint stability during the time course of fatigue.