Hip and trunk muscle electromyography differences between bilateral and unilateral bodyweight resistance exercises -A master’s thesis in Sports and Exercise Science – Human Performance

Background. Force production and movement in sports are predominantly performed in a unilateral weight-bearing stance, therefore a resistance training program should closely resemble sport specific unilateral leg kinetics. Hipand trunk-stabilizing muscle activity increases as the relative body weight balance changes from a bilateral to a unilateral stance, and these muscles are thought to play a central role in sports performance and injury prevention. Hip stabilizing muscles prevent internal rotation and medial adduction, therefore lacking strength in these muscles may well increase the quadriceps angle (QA). Aim. The aim of this study was (a) to examine the electromyographic (EMG) activity in hip and trunk muscles in three bodyweight exercises performed in a bilateral and a unilateral stance and, (b) to study the correlation between gluteus medius maximal voluntary contraction (MVC) activity and the QA in a drop-jump screening analysis. Methods. 14 healthy, young adults participated in a single session, single-group, observational study. Manual muscle testing was used to attain a MVC value for each specific muscle (gluteus medius (Gmed), gluteus maximus (Gmax), rectus abdominis (Rabd), and erector spinae (Espi)) and performed exercises were squat, bridge, and plank, both performed in a bilateral and a unilateral stance. A drop-jump screening analysis was performed to examine the correlation between Gmed MVC and the QA at the knee joint. Results. In all three exercises, there was a significant increase in EMG activity in the unilateral stance compared to the bilateral stance in both Gmed and Gmax (p< 0.05 for both muscles). Furthermore, in plank, there was a significant increase in trunk muscles (Rabd; p< 0.05, Espi; p< 0.05) in unilateral stance compared to the bilateral stance. In squat and bridge, no differences were identified in EMG activity for the trunk muscles (Rabd, Espi) between the bilateral and the unilateral stance. No correlation was found (r= 0.34) in the drop-jump screening analysis between Gmed MVC and the QA. Conclusion. Our results showed that all unilateral exercises activated (assessed by EMG) the hip muscles investigated (Gmed, Gmax) more than double compared to the same exercises performed bilaterally (except for Gmax in bridge). These results indicate that training performed on one leg activates hip stabilizing muscles to a greater degree than when the exercise is performed on two legs and, consequently, a unilateral training program might be beneficial for developing hip strength which is of great importance in sports performance as well as in injury prevention. Table of content Introduction ................................................................................................................................ 1 Background ................................................................................................................................ 2 Resistance training ................................................................................................................. 2 Unilateral training .................................................................................................................. 2 Core stability in bilateral and unilateral resistance training ................................................... 4 Knee valgus and injury prevention ......................................................................................... 6 Aim ......................................................................................................................................... 7 Methods ...................................................................................................................................... 8 Subjects and experimental design .......................................................................................... 8 Standardization ....................................................................................................................... 8 Electromyography and manual muscle testing ....................................................................... 8 The drop jump screening analysis ........................................................................................ 10 Ethics and social considerations ........................................................................................... 10 Statistical analysis ................................................................................................................ 11 Results ...................................................................................................................................... 11 Squat ..................................................................................................................................... 11 Bridge ............................................................................................................................... 13 Plank ................................................................................................................................. 14 The drop-jump screening analysis ........................................................................................ 15 Discussion ................................................................................................................................ 16 Results discussion ................................................................................................................ 16 Squat ................................................................................................................................. 16 Bridge ............................................................................................................................... 17 Plank ................................................................................................................................. 18 The drop-jump screening analysis .................................................................................... 18 Method discussion ................................................................................................................ 19 Conclusion ................................................................................................................................ 20 References ................................................................................................................................ 21 Appendix .................................................................................................................................. 24