Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB137

Poster Communications

Effects of knee joint angle and contraction intensity on quadriceps and hamstring coactivation in healthy young humans

R. Wu1,2, E. Delahunt1,2, M. Ditroilo1,2, M. Lowery3, G. De Vito1,2

1. School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland. 2. Institute for Sport and Health, University College Dublin, Dublin, Ireland. 3. School of Electrical, Electronic and Communications Engineering, University College Dublin, Dublin, Ireland.

  • Fig. 1: BF coactivation values (mean

  • Table 1: VL activation values (mean

Introduction: The coordination of agonist and antagonist muscles is essential for the correct execution of movements. For instance, the simultaneous activation of agonist-antagonist muscles (coactivation) is integral to the maintenance of knee joint stability (1). In this regard, it is logical to hypothesize that the coactivation of the quadriceps and hamstring muscles could depend on knee joint angle and contraction intensity. Therefore, we investigated the neural activation of the quadriceps and hamstring muscles during knee extension performed at different knee joint angles and contraction intensities in healthy young humans. Methods: 13 men (24.3 ± 2.8 years) and 13 women (23.4 ± 2.4 years) participated. Maximal voluntary isometric contraction (MVIC) of knee extensors (KE) and flexors was assessed at two knee joint angles (90° and 60°, 0° = full extension). At each angle, participants performed a 5 second isometric contractions at 20, 50 and 80% of KE MVIC in a random order. Surface EMG was recorded from vastus lateralis (VL) and biceps femoris (BF) muscles and the root mean square (RMS) amplitude calculated. To quantify the agonist (VL) and antagonist (BF) neural activity, at each contraction intensity, EMG RMS values for each muscle were normalized to the RMS amplitude for that muscle when acting as an agonist during MVIC at the same angle (2). Results: For BF coactivation, interactions for intensity × sex (p<.01) and intensity × angle (p<.01) were observed. Regardless of angle, women exhibited a higher level of BF coactivation with increasing contraction intensity than men (Fig. 1A). Additionally, irrespective of sex, the coactivation level was higher at 90° than at 60° with a more evident difference at higher intensities (Fig. 1B). VL activation increased with contraction intensity at 90° and 60° for both sexes with a more marked increment at 90° than 60° for women but not for men (Table 1). Conclusion: The main findings were: 1) a more flexed knee joint angle (90°) was associated with an augmented coactivation level; 2) a higher level of BF coactivation was observed at higher contraction intensities; 3) women exhibited a higher antagonist coactivation than men especially at the highest contraction intensity (80%MVIC). Overall, the observed increment in antagonist coactivation as a function of joint angle and contraction intensity may play an important role in maintaining joint stability by providing synergistic action to counteract the agonist's increasingly destabilizing influence. This is of particular relevance for women.

Where applicable, experiments conform with Society ethical requirements