Electromyographic analysis of hip extension movement using unstable surfaces

Purpose: Hip extension is an essential movement of lower body. Since there is a deep relation between hip region and lumbo-pelvic complex, the neuromuscular pattern involved in this movement should be trained for injuries prevention, sport conditioning and rehabilitation. Even if previous studies suggested how to train those muscle in different conditions, the role of unstable surfaces is still debate. The aim of this study is to investigate the activation of hamstring, glutes and lumbar muscles during static prone hip extension movements executed with specific tools and joint positions. Methods: Ten healthy and trained people volunteered for the study (8 male and 2 female, mean age 26,5 years). They performed unilateral hip extension movements in prone position using Mat, Bosu and Fitball. Each movement was executed in both side of the body (Right: R, Left: L) by holding static muscle contraction at 0° and 20° hip extension. People were lying prone on Mat and above unstable surfaces with knee in both extended (EXT) and 90° flexed (FLEX) positions. Muscle activity was recorded using electromyography (EMG) for biceps femoris (BF), gluteus maximus (GL) and lumbar erector spinae (LUM) in right and left side. Data were analyzed in order to compare unstable surfaces (Bosu and Fitball) with Mat (reference condition) and to quantify the role of stabilizing side of the body. Results: Muscle activity increased with progression of range of motion (from 0° to 20°) and level of instability (growing order: mat, Bosu, Fitball) for BF, GL and LUM (p<0.05) in relation to muscle’s functional role. BF showed higher values on Bosu and Fitball compared to Mat during R EXT, R FLEX, L EXT and L FLEX movements at 0° in both side of the body (p<0.05). Moreover, BF was higher on Fitball compared to Bosu in R EXT and R FLEX at 20° for left side (p<0.05) and Fitball compared to Mat in L FLEX for right side movements (p<0.01). GL significantly improved EMG on Bosu and Fitball compared to Mat at 0° in R EXT and R FLEX for right side (respectively, p<0.05 and p<0.01) , in L FLEX for left side (p<0.01) and in L EXT for both side (p<0.05). During 20° hip extension, GL activity was higher on Fitball compared to Bosu for R EXT in right side (p<0.05). LM EMG values were similar for movement side at 0° in R EXT, L EXT, R FLEX and L FLEX (p<0.05) , while Mat evidenced increased muscle activity compared to Bosu and Fitball in stabilizing side for R EXT (0° and 20°, p<0.01) and L EXT (20°, p<0.05). Conclusions: Bosu and Fitball are efficient tools to improve muscle activity during isometric hip extension movements. In comparison to Mat, BF and GL increase their activity using unstable surfaces with higher values at 20° in both FLEX and EXT conditions, while at 0° their highlight similar EMG (compared to Mat at 20°) with lower LUM recruitment. Moreover, GL and LUM evidence an important stabilizing function for lumbo-pelvic region on opposite side of movement when using Bosu and Fitball. Consequently, isometric prone hip extension movement can be an effective exercise for posterior muscle chain conditioning. Reference: - Boren K., Conrey C., Le Coguic J., Paprocki L., Voight M., Robinson TK.: "Electromyographic Analysis of Gluteus Medius and Gluteus Maximus during Rehabilitation Exercises", The International Journal of Sports Physical Therapy, 2011 Sep, 6(3): 206-223 - Jung H.S., Kang S.Y., Park J.H., Cymn H.S., Jeon H.S., “EMG activity and force during prone hip extension in individual with lumbar segmental instability”, Manual Therapy 20 (2015) 440-444