Electromyographic Analysis of the Shoulder Girdle Musculature during External Rotation Exercises

Background: Implementation of overhead activity, a key component of many professional sports, requires an effective and balanced activation of shoulder girdle muscles particularly during forceful external rotation motions. Purpose: The study aimed to identify activation strategies of 16 shoulder girdle muscles/muscle segments during common shoulder external rotational exercises. Study Design: Cross-Sectional Study Method: EMG was recorded in 30 healthy subjects from 16 shoulder girdle muscles/muscle segments (surface electrode: anterior, middle and posterior deltoid, upper, middle and lower trapezius, serratus anterior, teres major, upper and lower latissimus dorsi, upper and lower pectoralis major; fine wire electrodes: supraspinatus, infraspinatus, subscapularis and rhomboid major) using a telemetric EMG system. Five external rotation (ER) exercises (standing ER at 0o and 90o of abduction, and with under-arm towel roll, prone ER at 90o of abduction, side-lying ER with under-arm towel) were studied. Exercise EMG amplitudes were normalised to EMGmax (EMG at maximal ER force in a standard position). Univariate analysis of variance (ANOVA) and post-hoc analysis applied on EMG activity of each muscle to assess the main effect of exercise condition. Results: Muscular activity differed significantly among the ER exercises (P<0.05 – P<0.001). The highest activation for anterior and middle deltoid, supraspinatus, upper trapezius, and serratus anterior occurred during standing ER at 90o of abduction; for posterior deltoid, middle trapezius, and rhomboid during side-lying ER at 0° of abduction; for lower trapezius, upper and lower latissimus dorsi, subscapularis, and teres major during prone ER at 90o of abduction, and for clavicular and sternal part of pectoralis major during standing ER with Under-Arm Towel. Conclusion: Key glenohumeral and scapular muscles can be optimally activated during the specific ER exercises particularly in positions that stimulate athletic overhead motions. Clinical Relevance: These results enable sport medicine professionals to target specific muscles during shoulder rehabilitation protocols while minimising the effect of others, providing a foundation for optimal evidence-based exercise prescription. They also provide information for tailored muscle training and injury prevention in overhead sports

Movement Behavior of High-Heeled Walking: How Does the Nervous System Control the Ankle Joint during an Unstable Walking Condition?

The human locomotor system is flexible and enables humans to move without falling even under less than optimal conditions. Walking with high-heeled shoes constitutes an unstable condition and here we ask how the nervous system controls the ankle joint in this situation? We investigated the movement behavior of high-heeled and barefooted walking in eleven female subjects. The movement variability was quantified by calculation of approximate entropy (ApEn) in the ankle joint angle and the standard deviation (SD) of the stride time intervals. Electromyography (EMG) of the soleus (SO) and tibialis anterior (TA) muscles and the soleus Hoffmann (H-) reflex were measured at 4.0 km/h on a motor driven treadmill to reveal the underlying motor strategies in each walking condition. The ApEn of the ankle joint angle was significantly higher (p<0.01) during high-heeled (0.38±0.08) than during barefooted walking (0.28±0.07). During high-heeled walking, coactivation between the SO and TA muscles increased towards heel strike and the H-reflex was significantly increased in terminal swing by 40% (p<0.01). These observations show that high-heeled walking is characterized by a more complex and less predictable pattern than barefooted walking. Increased coactivation about the ankle joint together with increased excitability of the SO H-reflex in terminal swing phase indicates that the motor strategy was changed during high-heeled walking. Although, the participants were young, healthy and accustomed to high-heeled walking the results demonstrate that that walking on high-heels needs to be controlled differently from barefooted walking. We suggest that the higher variability reflects an adjusted neural strategy of the nervous system to control the ankle joint during high-heeled walking