Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

Abstract

Background: Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass (UWM) affects the muscular activity of the shoulder stabilizers. Aim of the study was to assess neuromuscular activity of dynamic shoulder stabilizers under four conditions of stable and UWM during three shoulder exercises. It was hypothesized that a combined condition of weight with UWM would elicit greater activation due to the increased stabilization demand. Methods: Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 s.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different exercise conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root-mean-square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; p ≤ 0.05; Bonferroni adjusted α = 0.008). Results: PWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p > 0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion: Higher weight generated greater muscle activation whereas an UWM raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an UWM increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.

Quadriceps and gluteus medius activity during stable and unstable loading exercises in athletes. A cross‐sectional study

“…1,9 There are other studies that have obtained similar results to ours in other regions of the body. Baritello et al 46 found that training with an unstable weight mass elicited higher muscle activity in the shoulder muscles when compared with a weight with stable mass behavior. Lawrence et al 47 observed that suspending barbell weights with elastic bands can increase trunk stabilizing muscle activity more than free weights.…”

Function, strength, and muscle activation of the shoulder complex in Crossfit practitioners with and without pain: a cross-sectional observational study

“…Symptomatic athletes present a reduction in the lower trapezius activity and an increase in the upper trapezius activity. and the increase in load tends to increase the intensity of the muscular activity [ 24 , 42 , 52 ]. Athletes whose sport involves aerial movements showed higher muscle strength compared to athletes from other sports [ 53 ].…”

Crossfit Practice: An Electromyographic Analysis of Masticatory Muscles

“…In sports training, it is necessary to consider the effectiveness of skeletal muscle activity and assess body response in relation to pre-established exercise, observing strength, endurance, and muscle activity [22,23]. Therefore, it is justi able to evaluate the electromyographic behavior of the masseter and temporalis muscles of participants who practice CrossFit exercise to understand whether there is a relationship between high-intensity sports and the functionality of the dynamic structures of the stomatognathic system.…”