Vibration as an adjunct to exercise: its impact on shoulder muscle activation.

PURPOSE: There is an interest within elite sport in understanding the impact of a vibrating platform as an adjunct to exercise in the training and rehabilitation of throwing athletes. However, there has been no comprehensive evaluation of its impact on the rotator cuff muscles or its effect on the timing of shoulder muscle recruitment more globally. METHODS: Twenty healthy participants were recruited with EMG recorded from 15 shoulder girdle muscles. Isometric shoulder flexion at 25% maximal voluntary contraction was performed in three testing scenarios [no vibration; whole body vibration (WBV); and arm vibration (AV)]. A press up and triceps dips with and without vibration were also performed. Muscular recruitment was assessed pre- and post-vibration exposure as participants initiated forward flexion. RESULTS: Activation of the anterior deltoid (p = 0.002), serratus anterior (p = 0.004), and rotator cuff muscles (p = 0.004-0.022) occurred significantly earlier following exposure to vibration. Significantly greater activation was seen in the anterior, middle and posterior deltoid, upper, middle and lower trapezius, serratus anterior, teres major, latissimus dorsi, supraspinatus, and infraspinatus when the isometric contraction was performed with either WBV and/or AV (p = < 0.001-0.040). Similarly, increased activation was also demonstrated during the press up and triceps dips when performed with vibration. CONCLUSION: The use of vibration as an adjunct to exercise provokes a near global increase in shoulder muscle activation level. Furthermore, exposure to vibration alters muscular recruitment improving readiness for movement. This has potential implications within elite sport for both training and game preparation; however, further longitudinal work is required.

Electromyographic activity of selected trunk, core, and thigh muscles in commonly used exercises for ACL rehabilitation.

[Purpose] Most of rehabilitation programmes for Anterior Cruciate Ligament (ACL) injury focus on quadriceps-hamstrings activation imbalances and less is known about kinetically linked muscles. This study investigated electromyographic activity of selected trunk, core, and thigh muscles during common rehabilitation exercises for ACL injury. [Subjects and Methods] Twelve active female volunteers participated in this cross-sectional laboratory study. Surface EMG was used to compare activation of eight trunk, hip/core, and lower limb muscles: Erector Spinae (ES), Rectus Abdominis (RA), Gluteus Maximus (GM), Vastus Lateralis (VL), Rectus Femoris (RF), Vastus Medialis (VM), Biceps Femoris (BF), and Semitendinosus (ST) during Forward Lunge, Double Leg Raise, Glute Bridge, Sit-Up, and Squat. [Results] Forward lunge produced significantly higher activation in the VM (61.1 ± 19.4), VL (59.2 ± 12.9), and RF (32.0 ± 2.6). Double leg raise generated highest activity in the RF (26.6 ± 2.8) and RA (43.3 ± 4.4); and Glute Bridge in the GM (44.5 ± 19.0) and BF (22.4 ± 4.3). Sit-up produced the highest activation in the RF (36.6 ± 4.7) followed by RA (18.9 ± 3.8). Squat produced a higher activation in VL (55.0 ± 12.9), VM (51.5 ± 18.2), and ES (40.4 ± 18.3). [Conclusion] This study provide further evidence for developing training programmes for ACL injury prevention and rehabilitation. A combination of exercises to reinstate quadriceps-hamstrings activation balance and enhance core stability is recommended.

Electromyographic analysis in elite swimmers with shoulder pain during a functional task.

The purpose of study was to determine and compare electromyographic activity of selected shoulder girdle muscles in elite swimmers with and without shoulder pain. Twelve professional swimmers with shoulder pain (mean age: 18.55 ± 3.16 years, body mass: 74.33 ± 2.91 kg and height: 179.00 ± 5.29 cm) and 12 swimmers without pain (mean age: 18.11 ± 1.61 years, body weight: 73.33 ± 6.06 kg, height: 178.33 ± 5.07 cm) were recruited. Surface electromyography signals were collected from seven upper limb muscles during a task: participants were instructed to mark points with a pen within each of the three circles counterclockwise. The normalised root-mean-square value was used to determine the muscular activation. Swimmers with shoulder pain demonstrated greater activation of the upper trapezius (pain group mean: 28.04 ± 10.37, control group mean: 13.40 ± 06.04; p = 0.002, ηp2: 0.455), serratus anterior (pain group mean: 30.78 ± 20.09, control group mean: 13.30 ± 5.52; p = 0.023, ηp2: 0.283) and latissimus dorsi (pain group mean: 27.05 ± 17.87, control group mean: 4.99 ± 3.90; p = 0.002, ηp2 : 0.450) muscles. There was no difference (p > 0.05) in the activation of the middle and lower trapezius, middle deltoid and sternocleidomastoid. The altered muscle activation patterns may contribute to the painful shoulder in elite swimmers and need to be considered within the rehabilitation interventions.

The Musculoskeletal Health Benefits of Tennis.

BACKGROUND: The prevalence of musculoskeletal (MSK) conditions is increasing, and although current guidelines for physical activity attempt to combat this, many fail to achieve the recommended targets. The present study sought to investigate whether regular tennis participation is more effective at enhancing MSK function than meeting the current international physical activity guidelines. HYPOTHESIS: Tennis players will display significantly enhanced MSK function when compared with age-matched healthy active nonplayers. STUDY DESIGN: Cross-sectional study. LEVEL OF EVIDENCE: Level 3. METHODS: Ninety participants (age range, 18-65 years) took part in this study; there were 43 tennis players (18 men, 25 women) and 47 nonplayers (26 men, 21 women). MSK function was assessed by cluster analysis of 3 factors: (1) electromyographic fatigability of prime movers during handgrip, knee extension, and knee flexion; (2) isometric strength in the aforementioned movements; and (3) body composition measured by bioelectrical impedance analysis. Maximal oxygen uptake was also assessed to characterize cardiorespiratory fitness. RESULTS: Tennis players displayed significantly greater upper body MSK function than nonplayers when cluster scores of body fat percentage, handgrip strength, and flexor carpi radialis fatigue were compared by analysis of covariance, using age as a covariate (tennis players, 0.33 ± 1.93 vs nonplayers, -0.26 ± 1.66; P < 0.05). Similarly, tennis players also demonstrated greater lower extremity function in a cluster of body fat percentage, knee extension strength, and rectus femoris fatigue (tennis players, 0.17 ± 1.76 vs nonplayers, -0.16 ± 1.70; P < 0.05). CONCLUSION: The present study offers support for improved MSK functionality in tennis players when compared with age-matched healthy active nonplayers. This may be due to the hybrid high-intensity interval training nature of tennis. CLINICAL RELEVANCE: The findings suggest tennis is an excellent activity mode to promote MSK health and should therefore be more frequently recommended as a viable alternative to existing physical activity guidelines.

Patterns of muscle coordination during dynamic glenohumeral joint elevation: An EMG study.

The shoulder relies heavily on coordinated muscle activity for normal function owing to its limited osseous constraint. However, previous studies have failed to examine the sophisticated interrelationship between all muscles. It is essential for these normal relationships to be defined as a basis for understanding pathology. Therefore, the primary aim of the study was to investigate shoulder inter-muscular coordination during different planes of shoulder elevation. Twenty healthy subjects were included. Electromyography was recorded from 14 shoulder girdle muscles as subjects performed shoulder flexion, scapula plane elevation, abduction and extension. Cross-correlation was used to examine the coordination between different muscles and muscle groups. Significantly higher coordination existed between the rotator cuff and deltoid muscle groups during the initial (Pearson Correlation Coefficient (PCC) = 0.79) and final (PCC = 0.74) stages of shoulder elevation compared to the mid-range (PCC = 0.34) (p = 0.020-0.035). Coordination between the deltoid and a functional adducting group comprising the latissimus dorsi and teres major was particularly high (PCC = 0.89) during early shoulder elevation. The destabilising force of the deltoid, during the initial stage of shoulder elevation, is balanced by the coordinated activity of the rotator cuff, latissimus dorsi and teres major. Stability requirements are lower during the mid-range of elevation. At the end-range of movement the demand for muscular stability again increases and higher coordination is seen between the deltoid and rotator cuff muscle groups. It is proposed that by appreciating the sophistication of normal shoulder function targeted evidence-based rehabilitation strategies for conditions such as subacromial impingement syndrome or shoulder instability can be developed.