Muscle activation during push-up exercise under stable and instable conditions

BACKGROUND: Push up exercise is a popular and common way of strengthening the upper body in clinical, fitness and sport fields. Recently, trainers and researchers suggest to perform this exercises under unstable condition with specific tools, in order to increase muscle activation. PURPOSE: The aim of this study is to investigate the electromyographic activity (EMG) of shoulder and trunk muscles during 4 different kind of isometric push up exercises performed with elbow flexed and extended. METHODS: Ten healthy subjects volunteered for the study. Three unstable conditions (TRX, BALL, SKIMMY) and one stable condition (STEP) for two different elbow joint angles (90° flexion – FLEX ; full extension - EXT) were tested during 5 seconds isometric push ups. EMG was recorded for Anterior Deltoids (DA), Pectoralis Major (GP), Triceps Brachialis (TRI), Latissimus Dorsi (GD), Rectus Abdomins (RA), Obliquus Externus (OE). Data were processed in order to calculate EMG Root Mean Square (RMS) and normalize to stable condition (Step). CONCLUSIONS: All unstable conditions show higher muscle activity in both joint angle positions compared to stable condition. In particular, TRX evidences the highest EMG data in FLEX and EXT condition: TRX is higher than BALL, STEP and SKIMMY in EXT condition (p<0.01) and higher than STEP and SKIMMY (p<0.01) in FLEX condition. TRB, RA and OE are the most activated muscles in all conditions for both FLEX and EXT with different values related to specific tools. GP, DA and GD are higher in FLEX than EXT (p<0.01) while RA is higher in EXT angle compared to FLEX (p<0.05). These findings suggest that adding instability is a good way to improve trunk muscle activity in both joint angle positions, while shoulder muscle activity is more related to elbow condition.