Muscular activation during plyometric exercises in 90° of glenohumeral joint abduction

Effect of Scapular Retraction on Lower Trapezius, Infraspinatus, and Deltoid Muscle Electromyographic Activity During the Side-Lying Abduction Exercise

Background

The lower trapezius (LT) muscle, which stabilizes the scapula posteriorly during arm elevation, has been interesting to both clinicians and researchers for its importance in throwing-related shoulder rehabilitation and injury prevention.

Purpose

The purpose of this study was to investigate the electromyographic activity of the LT and other relevant muscles during scapular and shoulder activities in the side-lying position.

Methods

Twenty collegiate baseball players volunteered to participate in this study. Electromyographic (EMG) output of the lower trapezius, infraspinatus, posterior deltoid, middle deltoid, serratus anterior, and upper trapezius muscles were collected. All the subjects performed isometric resistance exercises in four arm positions: 0° horizontal abduction from the coronal plane (NEUT) with protraction (NEUT-PRO), 15° horizontal adduction from the coronal plane (HADD) with protraction (HADD-PRO), and NEUT with retraction (NEUT-RET), and HADD-RET in a side-lying isometric abduction exercise with two external loads: a 9.1 kg dumbbell and 40% of the manual muscle test (MMT). The subjects also performed two more isometric resistance exercises: supine protraction and side-lying external rotation (ER) of the glenohumeral (GH) joint in GH adduction at 90° of GH ER or with as much ER as possible. All raw EMG data were normalized to maximal voluntary isometric contraction (% MVIC) of the corresponding muscle.

Results

LT activity was significantly greater in HADD-RET with 9.1 kg than that of HADD-PRO (p < 0.001) (55 vs 21% MVIC) while middle deltoid muscle activity was significantly decreased in both NEUT and HADD-RET compared to that of NEUT and HADD-PRO (p < 0.001). In contrast, IS muscle activity was significantly increased in HADD-RET with 9.1 kg compared with that 40% MMT (p < 0.001) (41 vs 22% MVIC).

Conclusion

LT activity was modulated by changes in scapulothoracic and glenohumeral joint positioning during a side-lying isometric abduction exercise. These findings may help clinicians to select exercises to improve scapular muscle balance ratios during rehabilitation of the shoulder complex.

Level of Evidence

Level 3b, Controlled laboratory study.

Reliability of Upper Extremity Functional Performance Tests for Overhead Sports Activities

Background

There is lack of consensus on which tests, particularly upper extremity functional performance tests (FPT) that should be used for clinical decision making to progress a patient through a rehabilitation program or criteria for return to sport (RTS). Consequently, there is a need for tests with good psychometric properties that can be administered with minimal equipment and time.

Purpose

(1) To establish the intersession reliability of several open kinetic chain FPT in healthy young adults with a history of overhead sport participation. (2) To examine the intersession reliability of the limb symmetry indices (LSI) from each test.

Study Design

Test-retest reliability, single cohort study.

Methods

Forty adults (20 males, 20 females) completed four upper extremity FPT during two data collection sessions three to seven days apart: 1) prone medicine ball drop test 90°shoulder abduction (PMBDT 90°), 2) prone medicine ball drop test 90°shoulder abduction/90° elbow flexion (PMBDT 90°-90°), 3) half-kneeling medicine ball rebound test (HKMBRT), 4) seated single arm shot put test (SSASPT). Measures of systematic bias, absolute reliability and relative reliability were computed between the sessions for both the original test scores and LSI.

Results

Except for the SSASPT, all tests demonstrated significant (p ≤ 0.030) improvements in performance during the second session. Generally, for the medicine ball drop/rebound tests, the absolute reliability was the highest (less random error) for the HKMBRT, next the PMBDT 90°followed by PMBDT 90°-90°. Excellent relative reliability existed for the PMBDT 90°, HKMBRT, and SSASPT, whereas fair to excellent relative reliability for the PMBDT 90°-90°. The SSASPT LSI revealed the highest relative and absolute reliability.

Conclusion

Two tests, HKMBRT and SSASPT demonstrated sufficient reliability; therefore, the authors' recommend those tests can be used for serial assessments to advance a patient through a rehabilitation program as well as criteria for progression to RTS.

Level of Evidence

3.

Rehabilitation and Return to Sport Following Elbow Injuries

Elbow injuries are frequently seen in throwing and overhead athletes. This review provides a framework for diagnosis, treatment, and particularly rehabilitation of common elbow pathologies, including ulnar collateral ligament injury, valgus extension overload, and medial and lateral epicondylitis. Advanced rehabilitation facilitates complete return to functional sport-specific activity and is based on objective criteria. As diagnostic and therapeutic modalities improve our understanding of elbow pathologies in the athletic patient, continued research will further elucidate objective evidence-based rehabilitation techniques.

A comparison of teres minor and infraspinatus muscle activation in the prone position

Background

Methods

Results

Conclusion

Rehabilitation Exercises for Dysfunction of the Scapula: Exploration of Muscle Activity Using Fine-Wire EMG

BACKGROUND

Scapular muscle activity during shoulder exercises has been explored with surface electromyography (EMG). However, knowledge about the activity of deeper-layer scapular muscles is still limited.

PURPOSE

To investigate EMG activation of the deeper-layer scapular stabilizers (levator scapulae [LS], rhomboid major [RM], pectoralis minor [Pm] muscles) together with superficial muscle activity (upper [UT], middle [MT], and lower trapezius [LT] and serratus anterior [SA]) during 4 exercises often used for training scapular function. Based on the amplitude EMG of the deeper-layer muscles, scapular muscle activation ratios for the 4 exercises were calculated, hereby providing knowledge of the optimal muscle balance.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 26 healthy participants performed 4 shoulder exercises (side-lying external rotation [ER], side-lying forward flexion, prone horizontal abduction with ER, and prone extension) while simultaneously measuring scapular muscle activity. Intramuscular electrodes were used for the deeper layer, in contrast to surface electrodes for the superficial muscles. All data were normalized to percentage of maximal voluntary isometric contraction (%MVIC), and the activation ratios (the muscle activity of the deeper layer relative to the other muscles) were calculated. A 1-way analysis of variance with Bonferroni correction was applied for statistical analysis.

RESULTS

Moderate activity was found in all exercises for the LS and RM (25%-45% MVIC). The Pm resulted in low activity during both side-lying exercises (13%-18% MVIC). Ratios involving LS or RM showed values >1 for all exercises (1.28-12.41) except for LS/MT, LS/LT, and LS/RM (0.85-0.98) during side-lying ER, and LS/MT, RM/MT and RM/LS (0.85-0.99) during side-lying forward flexion. Likewise, values <1 were found when MT (0.85) and LS (0.99) were involved with RM in the numerator during side-lying forward flexion. Ratios with Pm in the numerator showed values <1, apart from the ratios with UT and SA in the denominator.

CONCLUSION

The study provides extended knowledge about the deeper-layer scapular muscle activity and related ratios during the 4 shoulder exercises mentioned here. Putting theory into practice, based on our results, we advise both side-lying exercises to be performed to strengthen LT and MT, even in case of hyperactivity of the Pm. However, the 4 exercises should be given carefully to patients with hyperactivity in the LS and/or RM.

CLINICAL RELEVANCE

The findings of this study may assist clinical decision making in exercise selection for restoring scapular function.

Effects of Plyometric and Balance Training on Neuromuscular Control of Recreational Athletes with Functional Ankle Instability: A Randomized Controlled Laboratory Study

Plyometric exercise has been suggested for knee injury prevention in sports participation, but studies on ankle plyometric training are limited. This study aims to investigate the change of joint position sense and neuromuscular activity of the unstable ankle after six-week integrated balance/plyometric training and six-week plyometric training. Thirty recreational athletes with functional ankle instability were allocated into three groups: plyometric group (P) vs. plyometric integrated with balance training group (BP) vs. control group (C). Ankle joint position sense, integrated electromyography (EMG), and balance adjusting time during medial single-leg drop-landing tasks were measured before and after the training period. Following the six-week period, both training groups exhibited a lower absolute error in plantar flexion (P group: pre: 3.79° ± 1.98°, post: 2.20° ± 1.31°, p = 0.016; BP group: pre: 4.10° ± 1.87°, post: 2.94° ± 1.01°, p = 0.045), and the integrated group showed a lower absolute error in inversion angles (pre 2.24° ± 1.44° and post 1.48° ± 0.93°, p = 0.022), and an increased integrated EMG of ankle plantar flexors before landing. The plyometric group exhibited a higher integrated EMG of the tibialis anterior before and after landing (pre: 102.88 ± 20.93, post: 119.29 ± 38.33, p = 0.009 in post-landing) and a shorter adjusting time of the plantar flexor following landing as compared to the pre-training condition (pre: 2.85 ± 1.15 s, post: 1.87 ± 0.97 s, p = 0.006). In conclusion, both programs improved ankle joint position sense and muscle activation of the ankle plantar flexors during single-leg drop landing. The plyometric group showed a reduced adjusting time of the ankle plantar flexor following the impact from drop landing.

Does the Activity in Scapular Muscles During Plyometric Exercises Change When the Kinetic Chain Is Challenged?-An EMG Study

Werin, MB, Maenhout, AG, Icket, J, Jacxsens, N, Kempkes, E, and Cools, AM. Does the activity in scapular muscles during plyometric exercises change when the kinetic chain is challenged?-An EMG study. J Strength Cond Res XX(X): 000-000, 2020-Plyometric exercises for the shoulder are used in rehabilitation and in workout regime when the sport demands high speed power training. The aim of this clinical laboratory electromyography (EMG) study was to determine whether scapular muscle performance differs during plyometric shoulder exercises when changing the demand on the kinetic chain. Thirty healthy overhead athletes, with a mean age of 22.7 years (±2.2), performed 6 exercises, with both a low and a high demand on the kinetic chain, in prone, side and standing in positions. The EMG activity of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) on the tested side and bilateral of gluteus maximus (GM) and abdominal oblique externus (OE) was registered with wireless surface EMG. Intermuscular muscle ratios UT/SA, UT/MT, and UT/LT were also calculated. The level of significance set for the study was alpha = 0.05. The muscle ratio UT/SA was significantly lower (p < 0.05) when high demand on the kinetic chain compared with low. SA muscle activity showed significantly (<0.001) higher values in the prone position with high demand on the kinetic chain compared with low. All 3 trapezius muscle parts had significantly higher values (p < 0.001) in the prone compared with side and standing positions. The GM and OE showed significantly higher (p ≤ 0.01) activity in positions more demanding for the kinetic chain. When composing a strengthening or a rehabilitation program for athletes, the knowledge of how scapular and trunk muscles interact can be used to amplify the strengthening effect.

The Application of Double Elastic Band Exercise in the 90/90 Arm Position for Overhead Athletes

BACKGROUND

Traditional exercises performed with the shoulder in the position of 90° abduction and external rotation with elbow flexion (90/90) while using a single elastic band showed moderate activity of both the lower trapezius (LT) and infraspinatus (IS) muscle. The purpose of this study was to investigate activity of the teres minor (TMi) and the LT muscles during standing external rotation exercise with the shoulder in the 90/90 position with 2 elastic bands in both the frontal and the scapular plane.

HYPOTHESIS

TMi, IS, and LT muscle activities will vary depending on whether the shoulder is positioned in the frontal or scapular plane with the application of 2 elastic bands. Also, the serratus anterior (SA) and teres major (TMa) muscles will produce different muscular activity patterns during exercises performed with 2 elastic bands in the frontal plane compared with the TMi and LT muscles.

STUDY DESIGN

Controlled laboratory study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 21 collegiate baseball players volunteered to participate. The electromyography (EMG) activities of the TMi, IS, LT, SA, TMa, middle deltoid (MD), posterior deltoid, and upper trapezius (UT) muscles were measured with the 90/90 arm position during both isometric and oscillation resistance exercises with 2 elastic bands oriented in the frontal and scapular planes.

RESULTS

A significant difference was observed in EMG activity of both the TMi and the LT muscles between single and double elastic band applications in the frontal plane (P < 0.05). In contrast, EMG activity of the IS, SA, and TMa muscles was significantly increased in the scapular plane compared with the frontal plane (P < 0.05).

CONCLUSION

The standing 90/90 position effectively increased both TMi and LT muscle EMG activity with the double elastic band in the frontal plane while minimizing UT and MD muscle activity. EMG activity of the IS, SA, and TMa muscles increased with exercise in the scapular plane as compared with the frontal plane.

CLINICAL RELEVANCE

Oscillation movement under double elastic band application differentiated external rotator muscle and scapular muscle activities between the frontal and scapular plane during the 90/90 exercise in the frontal plane compared with the scapular plane. Clinicians can utilize each of the scapular and frontal positions based on their desired focus for muscular activation.

Analysis of Scapular Muscle EMG Activity During Elastic Resistance Oscillation Exercises From the Perspective of Different Arm Positions

BACKGROUND

Little is known about the optimal exercise intensity and the effects of arm position on elastic resistance exercise. The purpose of this study was to investigate scapular muscle activity in different arm positions utilized during standing elastic resistance exercise.

HYPOTHESIS

Lower trapezius (LT), serratus anterior (SA), and infraspinatus (IS) muscle activity will vary across arm positions above shoulder level. Also, oscillation resistance exercise will result in increased muscle activity compared with isometric contraction.

STUDY DESIGN

Controlled laboratory study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 19 uninjured male collegiate baseball players volunteered to participate in this study. The electromyography (EMG) activity of the LT, upper trapezius (UT), middle deltoid (MD), SA, and IS muscles was determined using surface EMG in 3 arm positions: diagonal pattern 1 (D1), 120° of shoulder abduction (120), and 90° shoulder abduction with external rotation and elbow flexion (90/90) during both isometric contraction and oscillation resistance exercise.

RESULTS

No difference in EMG activity of the LT muscle was found between the 120 and 90/90 position. However, the 120 position increased UT and MD muscle activity significantly more than those of the 90/90 position. The D1 arm position significantly increased SA muscle activity more than the 120 and 90/90 positions while the LT muscle activity was nearly silent.

CONCLUSION

The standing 90/90 position effectively generated both LT and IS muscle EMG activity while minimizing both UT and MD muscle activity.

CLINICAL RELEVANCE

The use of oscillation movements under elastic loading can create high muscle activation in the LT muscle without an adverse effect of the humeral head position and scapular rotation.

SCAPULAR MUSCLE ELECTROMYOGRAPHIC ACTIVITY DURING ABDUCTION EXERCISES IN THE SCAPULAR PLANE IN THREE POSITIONS

BACKGROUND

Hyperactivity of the anterior deltoid (AD) has been shown to produce adverse effects on subacromial space width as a result of humeral head superior translation during rehabilitation exercises used with overhead athletes. Also, the importance of the ratio of upper trapezius (UT) to lower trapezius (LT) muscle activity has been examined during rehabilitation exercises particularly for those who develop scapular dyskinesis.

HYPOTHESIS/PURPOSE

The purpose of this study was to investigate the level of LT and SA muscle activity during scapular plane elevation (scaption) in three positions while maintaining a moderate level of AD muscle activity. A secondary purpose was to identify the ratio of UT to LT muscle activity during the varied scaption exercises. The authors hypothesized that the activation of these two important muscles and the UT/LT ratio would vary with exercise position and throughout the range of scapular plane elevation.

METHODS

Fourteen active young subjects performed scaption exercises in three different positions: standing (STAN), quadruped (QUAD), and prone (PRON) with three different weight loads: 0 kg, 1.8 kg, and 4.1 kg. Surface electromyography (EMG) was used to record muscular activity. Tested muscles included the UT, LT, SA, AD, and posterior deltoid muscles on the dominant side.

RESULTS

QUAD scaption exercises with a load of 1.8 kg at 4 sec after the initial movement activated the LT muscle up to 49% of maximum voluntary isometric contraction (MVIC) while maintaining a moderate level of AD muscle activity (30% MVIC). STAN scaption exercises with the weight load of 1.8 kg at 3 sec after the initial movement activated 43% MVIC of the SA muscle while maintaining a moderate level of AD muscle activity (39% MVIC). The PRON condition generated significantly less SA muscle activity with both 1.8 and 4.1 kg weight loads than during the QUAD condition. The ratios of UT to LT muscle activity were significantly less in QUAD than those of STAN up to 4 sec after the initial movement. No significant difference was observed in the UT/LT ratio between QUAD and PRON conditions.

CONCLUSION

QUAD scaption exercise effectively activated both LT and SA muscles without over activating the AD and produced favorable ratios of UT to LT muscle activity.

LEVEL OF EVIDENCE

Descriptive Cohort Study, Level 4.

Effects of medicine ball mass on the intensity of 90°/90° plyometric throwing exercise

OBJECTIVES

To quantify the effects of medicine ball mass (1 kg, 1.5 kg, 2 kg) on the intensity of 90°/90° plyometric throwing exercise.

STUDY DESIGN

Controlled laboratory study.

SETTING

Biomechanics laboratory.

PARTICIPANTS

Fifteen physically active collegiate aged men.

MAIN OUTCOME MEASURES

Kinematics of the upper extremity were collected during completion of eight to ten repetitions of 90°/90° plyometric throwing exercise with three different mass medicine balls. Four parameters, medicine ball release and contact momentum, time-to-rebound, and contact time, were computed for each selected repetition and used for statistical analysis.

RESULTS

Ball mass did not significantly influence time-to-rebound (P = .718) and had a small (less than 0.05s) effect on ball contact time (P = .039). Ball release momentum was significantly greater (P < .001, 67-123% greater) than ball contact momentum. Medicine ball mass significantly increased both ball release (34-35%) and ball contact (45-67%) momentum however the effect was significantly greater for ball release momentum (P = .005).

CONCLUSIONS

These results document the effects of increasing medicine ball mass during 90°/90° plyometric throwing exercise and provide evidence for designing upper extremity plyometric training programs. Based on ball contact momentum being less than ball release momentum, as well as ball mass having greater influence on ball release velocity, we suggest that 90°/90° plyometric throwing exercise is a safe exercise.

Neuromuscular adaptations in shoulder function and dysfunction

Neuromuscular activity, organized in coordinated patterns, forms the basis of task-specific function in sports and exercise. The content and extent of these patterns may be variable, but include elements of activation/inhibition, co-activation, concentric/eccentric activation, proximal-to-distal activation, plyometric activation, and preactivation stiffness. They may be based on inherent neuromuscular architecture, but are commonly affected by positive or negative adaptations to imposed functional demands. Positive neuromuscular adaptations improve the efficiency of performing the task, which can result in less energy expenditure, maximum force delivered to the task, and protection of involved joints from excessive loads/motions, and improve the effectiveness of task performance. They frequently result from specific training in task mechanics and optimal conditioning of the neuromuscular structures involved in the task. Negative neuromuscular maladaptations can affect the efficiency of performing the task, increase energy expenditure and loads, decrease the effectiveness of task performance, and can be associated with clinical presentation of injury symptoms. They can result from overload, injury, and/or limited recovery. This chapter will focus specifically on shoulder joint function to provide examples of positive adaptations and negative maladaptations. It will then provide guidelines for clinical evaluation, treatment of clinical injury, and training/conditioning, based on understanding the neuromuscular activation.

Quality assessment of shoulder plyometric exercises: Examining the relationship to scapular muscle activity

OBJECTIVES

The purpose of the study was to evaluate performance quality of shoulder plyometric exercises, and examine the relationship to scapular muscle activation during an intense exercise bout.

DESIGN

Observational study.

SETTING

University laboratory.

PARTICIPANTS

32 healthy university students (male/female: 14/18) volunteers.

MAIN OUTCOME MEASURES

Subjects performed 10 plyometric exercises. Surface EMG of upper (UT), middle (MT) and lower (LT) trapezius and serratus anterior (SA) was registered. A quality assessment questionnaire was administered at the beginning and end of the exercise bout. Muscle activation at the beginning and end was evaluated by t-test. Mixed repeated measures ANOVA was conducted to test the effects of criterion-quality, time, muscles, exercises, and their interactions.

RESULTS

Increased EMG activation was noted in 34/40 cases, (21/40 significant (p < 0.05) changes). Quality assessment revealed a decline in the ability to maintain initial position (43% of subjects), failure to keep a consistent and symmetrical arc of motion (62% of subjects), and performance with trick movements (48% of subjects). Inability to keep a consistent arc of motion was significant in 4 exercises.

CONCLUSIONS

The novel questionnaire may aid quality assessment during plyometric exercises. Ability to keep a consistent arc of motion was the most sensitive marker of decline of performance quality.