The effect of six weeks endurance training on dynamic muscular control of the knee following fatiguing exercise H. Hassanlouei a , D. Falla b,c , L. Arendt-Nielsen a , U.G. Kersting a,⇑ a Center for Sensory-Motor Interaction, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Denmark b Department of Neurorehabilitation Engineering, Bernstein Focus Neurotechnology (BFNT) Göttingen, Bernstein Center for Computational Neuroscience, Georg-August University of Göttingen, Göttingen, Germany c Pain Clinic, Center for Anesthesiology, Emergency and Intensive Care Medicine, University Hospital Göttingen, Göttingen, Germany article info Article history: Received 26 June 2013 Received in revised form 23 May 2014 Accepted 10 June 2014 Keywords: Endurance training Centre of pressure Muscle fatigue abstract The aim of the study was to examine whether six weeks of endurance training minimizes the effects of fatigue on postural control during dynamic postural perturbations. Eighteen healthy volunteers were assigned to either a 6-week progressive endurance training program on a cycle ergometer or a control group. At week 0 and 7, dynamic exercise was performed on an ergometer until exhaustion and immediately after, the anterior–posterior centre of pressure (COP) sway was analyzed during full body perturbations. Maximal voluntary contractions (MVC) of the knee flexors and extensors, muscle fiber conduction velocity (MFCV) of the vastus lateralis and medialis during sustained isometric knee exten- sion contractions, and power output were measured. Following the training protocol, maximum knee extensor and flexor force and power output increased significantly for the training group with no changes observed for the control group. Moreover, the reduction of MFCV due to fatigue changed for the training group only (from 8.6% to 3.4%). At baseline, the fatiguing exercise induced an increase in the centre of pressure sway during the perturbations in both groups (>10%). The fatiguing protocol also impaired pos- tural control in the control group when measured at week 7. However, for the training group, sway was not altered after the fatiguing exercise when assessed at week 7. In summary, six weeks of endurance training delayed the onset of muscle fatigue and improved the ability to control balance in response to postural perturbations in the presence of muscle fatigue. Results implicate that endurance training should be included in any injury prevention program. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Maintaining balance is the ability to maintain the body’s centre of mass over the base of support during quiet standing and move- ment. These body oscillations are measured by the displacement of the COP resulting from centre of gravity movements of the individ- ual (Winter, 1995). Balance involves multiple sensory systems (visual, vestibular, and somatosensory), the motor system, and requires central nervous system integration (Punakallio, 2005). The task of maintaining balance is achieved without much diffi- culty during daily life. However, in the event of either an external perturbation (e.g., being pushed or nudged, walking on a compli- ant/slippery surface, changes in lighting) or an internal perturba- tion (e.g., muscle stiffness, musculoskeletal injury, fatigue), there is a tendency for postural sway to increase (Dickin and Doan, 2008) which, in the case of fatigue, may reduce static and dynamic regulation of balance. It has been well established that lower limb muscle fatigue may impair the proprioceptive and kinesthetic properties of joints (Miura et al., 2004) by increasing the threshold of muscle spindle discharge, disrupting afferent feedback, and subsequently altering conscious joint awareness (Gribble and Hertel, 2004) leading to decreased functionality of the proprioceptive muscle receptor sys- tem (Forestier et al., 2002). Therefore, altered somatosensory input due to muscle fatigue could result in deficits in neuromuscular and postural control around the joint (Gribble and Hertel, 2004), thereby making joint structures more susceptible to injury (Gollhofer et al., 1987). Studies have shown that fatigue reduced postural control measured using Star Excursion Balance Perfor- mance (SEBT) (Gribble and Hertel, 2004) and reduced EMG responses of the lower limbs when perturbed (Hedayatpour et al., 2011; Hassanlouei et al., 2012). Endurance training results in numerous adaptations within the skeletal muscle that may be significant for exercise performance, http://dx.doi.org/10.1016/j.jelekin.2014.06.004 1050-6411/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: uwek@hst.aau.dk (U.G. Kersting). Journal of Electromyography and Kinesiology 24 (2014) 682–688 Contents lists available at ScienceDirect Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin