Analysis of Muscle Recruitment Patterns During Shoulder Rehabilitation Exercises With and Without Elastic Resistance

Objectives: This investigation examined the muscle’s activation patterns of shoulder girdle principal muscles during a set of rehabilitation exercises. Methods: Thirty healthy participants (21 males, 9 females) performed a randomized set (12 repetitions at 2 s/repetition) of 7 exercises under natural and elastic loading conditions. The activation of 8 muscles was measured by surface electromyography (sEMG) and quantified as percentage of their maximal activation (%MVC). A linear encoder allowed to recognise the concentric and eccentric phases. Results: The execution time of 2 s was provided for most of exercises and conditions; however, females showed a higher variability especially in the elastic load condition. Considering a 20 %MVC as a sEMG threshold for low muscular activation, the ranking order of each muscle was determined for each exercise and loading conditions. By performing regression analysis with respect to the sEMG levels and ranking order, a neuromuscular cost can be evaluated and consequently the ability to perform the same work but with different efficiency. Conclusions: Linear and non-linear regression curves can be calculated and suggested as reference models. Hence the data presented here can be used as guideline for a more individualised rehabilitation programs or for specific tasks in the resistance strength training.