Acute effects of jaw clenching while wearing a customized bite-aligning mouthguard on muscle activity and force production during maximal upper body isometric strength.

Background/objectives: The possible mechanisms supporting the relationship between the masticatory and the musculoskeletal systems have been recently investigated. It has been suggested that jaw clenching promotes ergogenic effects on prime movers through the phenomenon of concurrent activation potentiation (CAP). The purpose of this study was to analyse the effects of jaw clenching and jaw clenching while wearing mouthguard (MG) on muscle activity and force output during three upper body isometric strength tests. Methods: Twelve highly trained rink-hockey athletes were recruited for the study. A randomized, repeated measures within study design was carried out to compare the acute effects of three experimental conditions: jaw clenching while wearing MG (MG), jaw clenching without MG (JAW) and non-jaw clenching (NON-JAW). Results: Statistical analyses revealed significant higher force output (p < 0.05) in all tests for MG conditions with respect to NON-JAW. When comparing JAW and NON-JAW conditions an increased peak force was found in handgrip (p = 0.045, d = 0.26) and bench press (p = 0.018, d = 0.43) but not in biceps curl (p = 0.562, d = 0.13). When comparing MG and JAW conditions, no differences were observed in any force output. In terms of muscle activity, significant differences were found in the agonist muscles of the handgrip test for MG with respect to NON-JAW (p = 0.031-0.046, d = 0.25-1.1). Conclusion: This study demonstrated that jaw clenching, with and without MG, may be a good strategy to elicit the CAP phenomenon, which seems to promote ergogenic effects in upper body isometric force production. The non-significant differences observed between JAW and MG suggested that the use of MG doesn't make a difference in enhancing the isometric force production neither the muscle activity in upper body isometric strength.

Superimposed vibration on suspended push-ups.

Background: Superimposition of vibration has been proposed in sports training using several devices and methods to enhance muscle activation and strength adaptations. Due to the popularity of suspension training, vibration systems have recently been developed to increase the effects of this training method. The present cross-sectional study aims to examine the effects of superimposing vibration on one of the most popular exercises in strength and conditioning programs: push-ups. Methods: Twenty-eight physically active men and women executed push-ups in three suspended conditions (non-vibration, vibration at 25 Hz, and vibration at 40 Hz). OMNI-Res scale was registered, and surface electromyographic signals were measured for the activity of the right and left external oblique, anterior deltoid, triceps brachii, sternal, and clavicular heads of the pectoralis major. Results: A linear mixed model indicated a significant fixed effect for vibration at 25 Hz and 40 Hz on muscle activity. Suspended push-ups with superimposed vibration (25 Hz and 40 Hz) showed a significant higher activity on left (25 Hz: p = 0.036, d = 0.34; 40 Hz: p = 0.003, d = 0.48) and right external oblique (25 Hz: p = 0.004, d = 0.36; 40 Hz: p = 0.000, d = 0.59), anterior deltoid (25 Hz: p = 0.032, d = 0.44; 40 Hz: p = 0.003, d = 0.64), and global activity (25 Hz: p = 0.000, d = 0.55; 40 Hz: p = 0.000, d = 0.83) compared to non-vibration condition. Moreover, OMNI-Res significant differences were found at 25 Hz (6.04 ± 0.32, p = 0.000 d = 4.03 CI = 3.27, 4.79) and 40 Hz (6.21 ± 0.36 p = 0.00 d = 4.29 CI = 3.49, 5.08) compared to the non-vibration condition (4.75 ± 0.32). Conclusion: Superimposing vibration is a feasible strategy to enhance the muscle activity of suspended push-ups.