The Effects of Fatigue on Muscle Synergies in the Shoulders of Baseball Players

Evaluation and Preparation of the Baseball Player in the Athletic Training Room

A critical aspect of the care of the baseball player involves understanding injury patterns, workload tolerance, and objective markers that can aid in identifying predisposing factors to injury. After injury, a well-structured rehabilitation program can return many players to the field. The greatest challenge is not only returning them to the previous level of performance but also preventing reinjury and maintaining durability. Potential factors implicated in the most common injuries include deficits in range of motion, balance, core strength, lumbopelvic control, thoracic rotation, posture, and muscle imbalance. Organizing an appropriate rehabilitation program with these factors in mind is critical.

Adaptive Modification in Agonist Common Drive After Combined Blood Flow Restriction and Neuromuscular Electrical Stimulation

Neuromuscular electrical stimulation (NMES) combined with blood flow restriction (BFR) has garnered attention in rehabilitation for its ability to enhance muscle strength, despite the potential to accelerate training-related fatigue. This study examined changes in force scaling capacity immediately following combined NMES and BFR, focusing on motor unit synergy between agonist pairs. Fifteen participants (23.3 ± 1.8 years) trained with combined BFR and NMES on the extensor carpi radialis longus (ECRL) muscle, with maximal voluntary contraction (MVC) of wrist extension, along with force and EMG in the ECRL and extensor carpi radialis brevis (ECRB), measured during a designate force-tracking before and after training. Factor analysis identified latent modes influencing motor unit coordination between the ECRB and ECRL. The results showed a significant decrease in MVC after training (p < 0.001). Post-test force fluctuations increased (p = 0.031), along with a decrease in the mean inter-spike interval (M_ISI) in the ECRL (p = 0.022). Factor analysis revealed an increase in the proportion of motor units (MUs) jointly regulated by the neural mode for both ECRB and ECRL, coupled with a decline in independently regulated MUs. Specifically, the proportion of MUs governed by the ECRL mode decreased, while those regulated by the ECRB mode increased. In conclusion, force generation capacity and force scaling are impaired after receiving combined NMES and BFR treatment. It involves redistribution of the common drive to MUs within two agonists, affecting the flexible coordination of muscle synergy and necessitating compensatory recruitment of MUs from the less fatigable agonist.

Changes in lower extremity muscle coordination over a 30-minute walk do not differ by muscle fatigability

Muscle fatigue, the transient decrease in muscle power, leads to low levels of physical activity and an inability to perform activities of daily living. Altered muscle coordination in response to fatigue may contribute to impaired physical performance. We sought to determine whether lower extremity muscle coordination during gait changes differently depending on susceptibility to fatigue (i.e., fatigability). Thirty-one older adults completed muscle power testing before and after a 30-min walk, with the change in power used to categorize participants as more or less fatigable. We used non-negative matrix factorization to identify muscle modules from electromyography (EMG) from the 2nd minute as our measure of baseline muscle coordination. Changes in muscle coordination were determined by computing the variance in the 30th minute's EMG accounted for by the baseline modules across all muscles (tVAF) and in individual muscles (mVAF). We compared tVAF between the 2nd and 30th minutes of the walk in individuals who were more and less fatigable. We used mVAF to explore the contribution of changes in individual muscle activity to tVAF. There was a decrease in tVAF overall in response to the walk (p < 0.001; 92.3 ± 1.6 % vs. 89.0 ± 4.3 %) but this did not differ between groups (interaction p = 0.66). There were significant associations between mVAF and tVAF for knee extensor, knee flexor, and ankle dorsiflexor muscles. Our results suggest that muscle coordination changes over the course of a walk in older adults but that this change does not differ between more and less fatigable older adults.

The effect of Dynamic tape's directional support on shoulder fatigue and pitching performance in amateur baseball players: a randomized crossover trial

BACKGROUND

To evaluate whether the application of Dynamic tape to the pitching shoulder could result in reduced shoulder fatigue, reduced delayed onset muscle soreness, or improved performance.

METHODS

This is a randomized crossover study, in which participants and investigators were blinded, included 20 amateur adult baseball players without shoulder pain. Sham taping and Dynamic taping were randomized, using an internal rotation support taping method in both groups. Bilateral shoulder strength and range of motion were measured with a handheld dynamometer and clinical goniometer before and after each test. The percentage of strength decrease, range of motion, pitch velocity, spin rate, and shoulder pain were recorded. The post-pitching decrease in strength and percentage of strength decrease were calculated by paired t-test and the pitching speed and spin rates in the innings for both the sham and Dynamic taping groups were analyzed using two-way ANOVA.

RESULTS

Compared with the sham group, the Dynamic tape group showed a significant loss in the percentage of strength decrease in internal rotation compared to the sham group (-1.4% vs. 7.0%, p = 0.03). However, no significant differences were observed in other strength declines, shoulder range of motion, pain, pitching velocity, or spin rate.

CONCLUSIONS

Dynamic tape reduced direction-specific shoulder fatigue but did not significantly enhance pitching performance or prevent delayed onset muscle soreness.

TRIAL REGISTRATION

ClinicalTrials: N201912094.

Assessment and indicators of kinematic behavior and perceived fatigability

OBJECTIVE

The objective of this study was to investigate the relationship between upper limb kinetics and perceived fatigability in elderly individuals during an upper limb position sustained isometric task.

METHODS

A total of 31 elderly participants, 16 men (72.94±4.49 years) and 15 women (72.27±6.05 years), performed a upper limb position sustained isometric task. Upper-limb acceleration was measured using an inertial measurement unit. Perceived fatigability was measured using the Borg CR10 scale.

RESULTS

Higher mean acceleration in the x-axis throughout the activity was associated with higher final perceived fatigability scores. Moderate correlations were observed between perceived fatigability variation and mean acceleration cutoffs in all axes during the second half of the activity. In women, significant correlations were found between all perceived fatigability cutoffs and mean acceleration in the y- and x-axes. However, in men, the relationships between perceived fatigability variation and mean acceleration were more extensive and stronger.

CONCLUSION

The acceleration pattern of the upper limb is linked to perceived fatigability scores and variation, with differences between sexes. Monitoring upper limb acceleration using a single inertial measurement unit can be a useful and straightforward method for identifying individuals who may be at risk of experiencing high perceived fatigability or task failure.

Assessment of Self-report, Palpation, and Surface Electromyography Dataset During Isometric Muscle Contraction

Measuring muscle fatigue involves assessing various components within the motor system. While subjective and sensor-based measures have been proposed, a comprehensive comparison of these assessment measures is currently lacking. This study aims to bridge this gap by utilizing three commonly used measures: participant self-reported perceived muscle fatigue scores, a sports physiotherapist's manual palpation-based muscle tightness scores, and surface electromyography sensors. Compensatory muscle fatigue occurs when one muscle group becomes fatigued, leading to the involvement and subsequent fatigue of other muscles as they compensate for the workload. The evaluation of compensatory muscle fatigue focuses on nine different upper body muscles selected by the sports physiotherapist. With a cohort of 30 male subjects, this study provides a valuable dataset for researchers and healthcare practitioners in sports science, rehabilitation, and human performance. It enables the exploration and comparison of diverse methods for evaluating different muscles in isometric contraction.

A Study of Racket Weight Adaptation in Advanced and Beginner Badminton Players

The jump smash is the most aggressive manoeuvre in badminton. Racket parameters may be the key factor affecting the performance of jump smash. Previous studies have focused only on the biomechanical characteristics of athletes or on racket parameters in isolation, with less observation of the overall performance of the human-racket system. This study aims to explore the effects of different racket weights on neuromuscular control strategies in advanced and beginner players. Nonnegative matrix factorisation (NMF) was used to extract the muscle synergies of players when jumping smash using different rackets (3U, 5U), and K-means clustering was used to obtain the fundamental synergies. Uncontrolled manifold (UCM) analyses were used to establish links between synergy and motor performance, and surface electromyography (sEMG) was mapped to each spinal cord segment. The study found significant differences (P  < 0.05) in the postural muscles of skilled players and significant differences (P  < 0.001) in the upper-limb muscles of beginners when the racket weight was increased. Advanced players adapt to the increase in racket weight primarily by adjusting the timing of the activation of the third synergy. Combined synergy in advanced players is mainly focused on the backswing, while that in beginners is mainly focused on the frontswing. This suggests that advanced players may be more adept at utilising the postural muscles and their coordination with the upper-limb muscles to adapt to different rackets. In addition, the motor experience can help athletes adapt more quickly to heavier rackets, and this adaptation occurs primarily by adjusting the temporal phase and covariation characteristics of the synergies rather than by increasing the number of synergies.

A long short-term memory modeling-based compensation method for muscle synergy

Muscle synergy containing temporal and spatial patterns of muscle activity has been frequently used in prediction of kinematic characteristics. However, there is often some discrepancy between the predicted results based on muscle synergy and the actual movement performance. This study aims to propose a new method for compensating muscle synergy that allows the compensated synergy signal to predict kinematic characteristics more accurately. The study used the change of direction in running as background. Non-negative matrix factorisation was used to extract the muscle synergy during the change of direction at different angles. A non-linear association between synergy and the height of pelvic mass centre was established using long and short-term memory neural networks. Based on this model, the height fluctuations of the pelvic centre of mass are used as input and predict the fluctuations of the synergy which were used to compensate for the original synergy in different ways. The accuracy of the synergies compensated in different ways in predicting pelvic centre of mass movement was then assessed by back propagation neural networks. It was found that the compensated synergy significantly improves accuracy in predicting pelvic centre of mass displacement (R2, p < 0.05). The predicted results of all-compensation are significantly different from actual performance in the end-swing (p < 0.05). The predicted results of half-compensation do not differ significantly from the actual performance, and its damage to the original synergy is smaller and does not increase with angle compared to all-compensation. The all-compensation may be affected by individual variability and lead to increased errors. The half-compensation can improve the predictive accuracy of the synergy while reducing the adjustment to the original synergy.

Upper-Limb Kinematic Behavior and Performance Fatigability of Elderly Participants Performing an Isometric Task: A Quasi-Experimental Study

Upper-limb position-sustained tasks (ULPSIT) are involved in several activities of daily living and are associated with high metabolic and ventilatory demand and fatigue. In older people, this can be critical to the performance of daily living activities, even in the absence of a disability.

OBJECTIVES

To understand the ULPSIT effects on upper-limb (UL) kinetics and performance fatigability in the elderly.

METHODS

Thirty-one (31) elderly participants (72.61 ± 5.23 years) performed an ULPSIT. The UL average acceleration (AA) and performance fatigability were measured using an inertial measurement unit (IMU) and time-to-task failure (TTF).

RESULTS

The findings showed significant changes in AA in the X- and Z-axes (p < 0.05). AA differences in women started earlier in the baseline cutoff in the X-axis, and in men, started earlier between cutoffs in the Z-axis. TTF was positively related to AA in men until 60% TTF.

CONCLUSIONS

ULPSIT produced changes in AA behavior, indicative of movement of the UL in the sagittal plane. AA behavior is sex related and suggests higher performance fatigability in women. Performance fatigability was positively related to AA only in men, where movement adjustments occurred in an early phase, though with increased activity time.

The dynamic control ratio and its equilibrium point: A preliminary study of isokinetic fatiguing internal-external rotational effort of the shoulder joint in healthy subjects

The shoulder joint-related dynamic control ratio (DCR) is derived by dividing the peak eccentric moment of the external rotators (ER) by the peak concentric moment of the internal rotators (IR). However, given the inherent limitation associated with a single value DCR, an alternative approach is to calculate it at fixed angular intervals. This preliminary study aimed at exploring the variation in the DCR at a resolution of 1° and under fatiguing external and internal rotation exertions. Eighteen young men, 10 experienced and 8 without experience in overhead sporting activities completed two separate series of 45 ER eccentric and 45 IR concentric isokinetic repetitions at 120°/s. The analysis focused on repetitions 1-3 (TR1), 21-23 (TR2) and 41-43 (TR3). The relative fatigue values for both muscle groups and for both E and NE participants were 25-40% with significantly higher fatigue resistance in eccentric compared with concentric exertions. The DCR traces varied substantially linearly for most of the internal rotation range of motion while significant differences (p < 0.001) were found in their values within group between TR1, TR2 and TR3 and between experienced and non-experienced participants. An antagonistic moment equilibrium (DCR = 1) was reached in all instances and for both groups only during TR3 with a significant progressive reduction in this moment as fatigue increased. Thus, considering the DCR as an angle-based variable rather than a single value isokinetic parameter, may add new insight regarding the interplay between the rotatory muscles of the shoulder joint.

Difference in muscle synergies of the butterfly technique with and without swimmer's shoulder

This study aimed to investigate whether muscle synergy differs between swimmers with and without swimmer's shoulder in the butterfly technique. Muscle synergies, which can assess muscle coordination, were analyzed using surface electromyography. Twenty elite swimmers were included in this study (swimmer's shoulder: n = 8; control: n = 12). The motions involved in executing the butterfly technique were classified into the early pull-through, late pull-through, and recovery phases. Muscle synergy data analyzed using the nonnegative matrix factorization method were compared between the two groups.

The swimming velocities were 1.66 ± 0.09 m・s ⁻¹ and 1.69 ± 0.06 m・s ⁻¹ for the control and swimmer's shoulder groups, respectively. Four muscle synergies in both groups were identified: synergy #1, which was involved in the early pull; synergy #2, involved in the late pull; synergy #3, involved in the early recovery; and synergy #4, involved in pre- and posthand entry. Compared to the control group, the swimmer's shoulder group had a small contribution from the pectoralis major (p = 0.032) and a high contribution from the rectus femoris during the early pull phase (p = 0.036). In the late pull phase, the contribution of the lower trapezius muscle in the swimmer's shoulder group was low (p = 0.033), while the contribution of the upper trapezius muscle in the pre- and postentry phases was high (p = 0.032). In the rehabilitation of athletes with swimmer's shoulder, it is therefore important to introduce targeted muscle rehabilitation in each phase.