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Effect of Knee Joint Angle and Contraction Intensity on Hamstrings Coactivation


R Wu, E Delahunt AND M Ditroilo, Madeleine Lowery, G DE Vito

Publication Type: 
Refereed Original Article
Purpose: This study investigated the effect of knee joint angle and contraction intensity on the co-activation of the hamstring muscles (when acting as antagonists to the quadriceps) in young and older individuals of both sexes. Methods: 25 young (24 ? 2.6 years) and 26 older (70 ? 2.5 years) healthy men and women participated. Maximal voluntary isometric contraction (MVIC) of the knee extensors (KE) and flexors was assessed at two knee joint angles (90? and 60?, 0? = full extension). At each angle, participants performed submaximal contractions of the KE (20%, 50% and 80% MVIC), while surface electromyography (EMG) was simultaneously acquired from the vastus lateralis and biceps femoris muscles to assess the level (EMG RMS) of agonist activation and antagonist co-activation. Subcutaneous adipose tissue in the areas corresponding to surface EMG electrode placements was measured via ultrasonography. Results: The contractions performed at 90? knee flexion demonstrated higher levels of antagonist co-activation (all p < 0.01) and agonist activation (all p < 0.01) as a function of contraction intensity compared to the 60? knee flexion. Furthermore, after controlling for subcutaneous adipose tissue, older participants exhibited a higher level of antagonist co-activation at 60? knee flexion compared with young participants (p < 0.05). Conclusions: The results of the present study suggest that (1) the antagonist co-activation is dependent on knee joint angle and contraction intensity; (2) subcutaneous adipose tissue may have an impact on the measured co-activation level likely because of a cross-talk effect. Antagonist co-activation may play a protective role in stabilizing the knee joint and maintaining constant motor output. Effect of Knee Joint Angle and Contraction Intensity on.... Available from: [accessed May 03 2018].
Digital Object Identifer (DOI): 
Publication Status: 
Date Accepted for Publication: 
Tuesday, 1 August, 2017
Publication Date: 
Medicine and science in sports and exercise
Research Group: 
National University of Ireland, Dublin (UCD)
Open access repository: