Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, PC69
Muscle activation patterns in the lower back and lower limb of normal subjects during balance tasks
N. Greenwood1, L. Duffell1, A. H. McGregor1
1. Department of Surgery and Cancer, Imperial College London, London, United Kingdom.
Muscle activation patterns used to maintain balance during quiet standing and during tasks that perturb an individual’s balance are not well established. In the maintenance of balance people may use a range of different strategies, which could place greater loads on certain joints and predispose these individuals to conditions such as osteoarthritis (Bennell et al, 2008) or lower back pain. It is important to establish normal muscle activation patterns in order to identify differences in people with or at high risk of developing such conditions; it may then be possible to use training programmes to alter these recruitment patterns and reduce undue loading on the joints. Ten subjects (6 female) gave informed consent. Mean (±SD) age, height and body mass were 27.6 (6.6) years, 173.1 (11.3) cm and 68.4 (7.9) kg, respectively. Surface electromyographic (EMG) recordings were taken from the erector spinae (ES), gluteus medius (GM), rectus femoris, semitendinosus, tibialis anterior (TA) and lateral gastrocnemius of the subjects’ dominant side. Initially subjects carried out maximum voluntary contractions of the measured muscles. They were then requested to perform 6 tasks each for 30 seconds while EMG data were collected; i) quiet standing (QS), eyes open; ii) QS, eyes closed; iii) one-leg standing (OLS), eyes open; iv) OLS, eyes closed; v) one-leg standing on a wobble board (OLW), eyes open and; vi) OLW, eyes closed. All ‘one-leg’ tasks were carried out on the dominant leg and loss of balance was recorded with markers. Overall muscle activity increased with increasing task difficulty (OLW>OLS>QS). In particular, activity of ES, GM and TA were significantly greater during OLS and OLW compared with QS in ‘eyes closed’ tasks (P<0.05). During the OLS task, activity of ES and TA were significantly higher when subjects had their eyes closed compared with eyes open (P<0.05). Over the 30s task duration, variation in the activity of each muscle was significantly higher during OLW compared with both QS and OLS tasks. The subjects that lost their balance tended also to have lower activation of ES (10.3 (6.5) vs 28.4 (12.9)%) and GM (9.2 (4.7) vs 18.1 (8.3)%) during the ‘one leg’ tasks. ES, TA and GM were the most important muscles for maintaining balance when normal balance (i.e. QS, eyes open) was challenged. In particular subjects were less successful in maintaining balance if they had lower activation of ES and GM. It has been suggested that reduced hip abductor activation results in higher medial knee joint loading, which may increase risk of OA development (Chang et al, 2005, Mundermann et al, 2005). Future work should focus on identifying differences in muscle activation patterns of people with conditions such as osteoarthritis and to establish if it is possible to alter these patterns using training programmes.
Where applicable, experiments conform with Society ethical requirements