Influence of fatigue on upper limb muscle activity and performance in tennis

The Influence of Fatigue, Recovery, and Environmental Factors on the Body Stability of Construction Workers

In the construction industry, falls, slips, and trips (FST) account for 42.3% of all accidents. The primary cause of FST incidents is directly related to the deterioration of workers' body stability. To prevent FST-related accidents, it is crucial to understand the interaction between physical fatigue and body stability in construction workers. Therefore, this study investigates the impact of fatigue on body stability in various construction site environments using Dynamic Time Warping (DTW) analysis. We conducted experiments reflecting six different fatigue levels and four environmental conditions. The analysis process involves comparing changes in DTW values derived from acceleration data obtained through wearable sensors across varying fatigue levels and construction environments. The results reveal the following changes in DTW values across different environments and fatigue levels: for non-obstacle, obstacle, water, and oil conditions, DTW values tend to increase as fatigue levels rise. In our experiments, we observed a significant decrease in body stability against external environments starting from fatigue Levels 3 or 4 (30% and 40% of the maximum failure point). In the non-obstacle condition, the DTW values were 9.4 at Level 0, 12.8 at Level 3, and 23.1 at Level 5. In contrast, for the oil condition, which exhibited the highest DTW values, the values were 10.5 at Level 0, 19.1 at Level 3, and 34.5 at Level 5. These experimental results confirm that the body stability of construction workers is influenced by both fatigue levels and external environmental conditions. Further analysis of recovery time, defined as the time it takes for body stability to return to its original level, revealed an increasing trend in recovery time as fatigue levels increased. This study quantitatively demonstrates through wearable sensor data that, as fatigue levels increase, workers experience decreased body stability and longer recovery times. The findings of this study can inform individual worker fatigue management in the future.

Biophysical characterization of the tennis serve: A systematic scoping review with evidence gap map

OBJECTIVES

We aimed to assess the available evidence on the biophysics of the tennis serve, mapping the populations, interventions, contexts and other relevant information to highlight what is already known and to identify gaps in the literature.

DESIGN

Systematic scoping review with evidence gap map.

METHODS

The protocol was designed according to PRISMA 2020, Prisma-ScR guidelines and the Cochrane Handbook. The searches were conducted on July 20, 2022 and updated on April 1, 2023, in PubMed, Scopus and Web of Science (core collection). The risk of bias assessment was performed using the Cochranes method for nonrandomized studies (RoBANS) and a narrative synthesis of the main findings was performed and supplemented with an evidence gap map.

RESULTS

Most trials were found on serve kinematics and kinetics (95 %), analyzing only flat serves (84 and 72 %, respectively). Few trials focused on physiology (20 %; e.g. biomarkers), under-19, left or both-handed, female and intermediate beginner or starter players (29, 17, 8 and 7 %, respectively). We found a preponderance of low and unclear risk of bias (63 and 31 %, respectively) and only 7 % high, particularly, on the assessment of confounding variables.

CONCLUSIONS

The current scoping review reveals a few trials on physiological rather than biomechanical variables, as well as the absence of the kick and slice serve, foot-back and foot-up serve, and left-handed, female, and young player analyses. We did not find systematic mistakes or limitations in the design, conduct, or analysis that would distort the results, since only 7 % presented a high risk of bias.

Exercise-Induced Fatigue Impairs Change of Direction Performance and Serve Precision among Young Male Tennis Players

This study investigates the effect of exercise-induced fatigue on change of direction performance and serve precision among young tennis players. A group of 21 players (age 12.90 ± 0.76 years), ranked among the top 50 players on the national tennis federation scale and the top 300 on the "Tennis Europe" scale, participated in the study. They underwent a standardized physiological load protocol using the "300-m running test" which consists of consecutive runs for 15 shares of 20 m (15 × 20). Its intensity was determined using the Borg Rating of Perceived Exertion (RPE) scale where subjects evaluated their level of experienced load on a scale from 0 to 10. Prior to and after the protocol, they performed a pre-planned change of direction T-test and serve precision test. Results showed significant increase of time in the T-test (from 11.75 ± 0.45 s to 12.99 ± 0.4 s, p = 0.00) and decrease in serve precision parameter from (6.00 ± 1.04 to 4.00 ± 1.26, p = 0.00) after the fatigue test protocol. The RPE increased from 5 to 9, after the fatigue protocol, indicating the desired fatigue effect. These findings indicate that exercise-induced fatigue impairs change of direction performance and serve precision among young tennis players.

Comparison of Grip Strength, Forearm Muscle Activity, and Shock Transmission between the Forehand Stroke Technique of Experienced and Recreational Tennis Players Using a Novel Wearable Device

Upper limb tennis injuries are primarily chronic, resulting from repetitive overuse. We developed a wearable device which simultaneously measures risk factors (grip strength, forearm muscle activity, and vibrational data) associated with elbow tendinopathy development resulting from tennis players' technique. We tested the device on experienced (n = 18) and recreational (n = 22) tennis players hitting forehand cross-court at both flat and topspin spin levels under realistic playing conditions. Using statistical parametric mapping analysis, our results showed that all players showed a similar level of grip strength at impact, regardless of spin level, and the grip strength at impact did not influence the percentage of impact shock transfer to the wrist and elbow. Experienced players hitting with topspin exhibited the highest ball spin rotation, low-to-high swing path brushing action, and shock transfer to the wrist and elbow compared to the results obtained while hitting the ball flat, or when compared to the results obtained from recreational players. Recreational players exhibited significantly higher extensor activity during most of the follow through phase compared to the experienced players for both spin levels, potentially putting them at greater risk for developing lateral elbow tendinopathy. We successfully demonstrated that wearable technologies can be used to measure risk factors associated with elbow injury development in tennis players under realistic playing conditions.

Physiological demands in simulated tennis matches and hitting tests take account of the translational and rotational kinetic energy ratio of the ball

Assessment of fatigue effect on hitting ability in tennis has been controversial in previous studies. The purpose of this study was to determine the relationship between player fatigue and groundstroke type in tennis. We hypothesized that subjects with higher blood lactate concentration during play would apply heavier spin to the ball. We divided players into two groups based on their blood lactate concentration during a pre-measured hitting test (HIGH and LOW). Each group performed a simulated match-play protocol consisting of repeated running and hitting tests, which simulated a three-set match. Heart rate, percent of heart rate reserve, oxygen uptake, pulmonary ventilation, and respiratory exchange were measured. The distance between the ball's landing point and the target, and the ball's kinematics, were recorded during the hitting test between sets. We found no significant difference in ball kinetic energy between groups, but the HIGH group hit the ball with a greater ratio of rotational kinetic energy to total kinetic energy. However, the progression of the simulation protocol did not affect physiological responses (including blood lactate concentration) or hitting ability. Therefore, it is suggested that the type of groundstrokes used by players is one of the factors that should be considered when discussing fatigue in tennis.

Shoulder Torque Production and Muscular Balance after Long and Short Tennis Points

Tennis is an asymmetric sport characterized by a systematic repetition of specific movements that may cause disturbances in muscular strength, power, and torque. Thus, we assessed (i) the torque, power, ratio production, and bilateral asymmetries in the shoulder's external and internal rotations at 90 and 180°/s angular velocities, and (ii) the point duration influence of the above-mentioned variables. Twenty competitive tennis players performed external and internal shoulder rotations; an isokinetic evaluation was conducted of the dominant and non-dominant upper limbs before and after five and ten forehands. A higher torque production in the shoulder's internal rotations at 90 and 180°/s was observed for the dominant vs. non-dominant sides (e.g., 63.1 ± 15.6 vs. 45.9 ± 9.8% and 62.5 ± 17.3 vs. 44.0 ± 12.6% of peak torque/body mass, p < 0.05). The peak torque decreased only after ten forehands (38.3 ± 15.8 vs. 38.2 ± 15.8 and 39.3 ± 16.1 vs. 38.1 ± 15.6 Nm, respectively, p < 0.05), but without impacting speed or accuracy. Unilateral systematic actions of tennis players caused contralateral asymmetries, evidencing the importance of implementing compensatory training. The forehand kinematic assessment suggests that racket and wrist amplitude, as well as speed, are important success determinants in tennis.

Determinant Physical Factors of Tennis Serve Velocity: A Brief Review

PURPOSE

To review the main physical aspects that could positively or negatively influence serve velocity (SV).

METHODS

An examination of existing literature including studies analyzing positive (biomechanical aspects, anthropometrics, range of motion, strength, and power) and negative (competition-induced fatigue) associations to SV are summarized in this review.

RESULTS

Aspects such as lower-leg drive, hip and trunk rotations, upper-arm extension, and internal rotation seem to be the major contributors to racquet and ball speed. Favorable anthropometric characteristics, such as body height, arm length, and a greater lean body mass, seem to positively influence SV. Also, strength indicators such as maximal isometric strength and rate of force development in specific joint positions involved in the kinetic chain alongside upper-body power seem to be related to faster serves. On the other hand, the effects of prolonged or repetitive match play may impair the aforementioned factors and negatively influence SV.

CONCLUSIONS

Following specific serving models that seem to enhance velocity production and efficient motion is highly recommended. Moreover, achieving a higher impact point, alongside shifting body composition toward a greater lean body mass, will most likely aid toward faster serves. Programs aiming at improving maximal isometric strength and rate of force development in specific positions involved in the kinetic chain including stretch-shortening cycle predominance and the mimicking of the serve motion seem of great interest to potentially increase SV. Effective recovery and monitoring of these variables appear to be essential to avoid impairments produced by continued or repetitive competition loads.

Upper Extremity Kinematics and Electromyographic Activity in Uninjured Tennis Players

There has been an increase in ulnar-sided wrist pain among tennis players. The purpose of this study was to establish a normative dataset of kinematic and electromyography (EMG) data during the forehand and two-handed backhand groundstrokes. In total, 20 adolescent United States Tennis Association (USTA) ranked tennis players (11/20 Male, Age = 15.0 ± 1.8 years, Height = 1.7 ± 1.1 m, BMI = 21.3 ± 3.4 kg/m2, 18/20 right-arm dominant) participated in this study. Kinematics (range of motion and angular velocity) and EMG data were simultaneously acquired during the forehand and two-handed backhand groundstrokes. Minimal differences were found between groupings of age, sex, and USTA ranking. The two-handed backhand groundstroke is characterized by bilaterally flexed elbows and ulnarly deviated wrists, with a flexed wrist and pronated forearm on the non-dominant side and an extended wrist and supinated forearm on the dominant side. EMG activation occurs bilaterally by peak backswing. The forehand groundstroke is characterized by a flexed elbow, pronated forearm, and ulnarly deviated and extended wrist. The wrist is at maximum ulnar deviation at ball impact. This study established an initial foundation for normative data for the forehand and two-handed backhand groundstrokes, which can be used for injury detection, rehabilitation, prevention, and ultimately performance improvement of tennis athletes.

Inter-Limb Muscle Property Differences in Junior Tennis Players

The goal of this study was to investigate side-to-side differences and asymmetries regarding muscle characteristics in young tennis players. Thirty-four participants performed contractile property measurements (stiffness, tone, elasticity and time to relaxation) on the dominant and non-dominant extremities including nine muscle groups involved in the kinetic chain of main tennis strokes. Significant differences (p≤0.05) and small-to-moderate effect sizes for greater stiffness and tone were found for the dominant biceps femoris (-11.1% and -5.6%; ES=0.53 and 0.54) and the non-dominant vastus medialis (5.4% and 3.2%; ES=-0.33 and -0.41), while greater tone was present in the non-dominant pectoralis major (4.0%; ES=-0.56). Time to relaxation was increased in the dominant biceps femoris (10.3%; ES=-0.58), the non-dominant pectoralis major (5.1%; ES=-0.56) and the gastrocnemius (9.1%; ES=-0.5). The non-dominant infraspinatus and dominant rectus abdominis showed greater elasticity than contralateral muscles (9.9% and -8.0%; ES=-0.58 and 0.6, respectively). These results reflect the existence of small-to-moderate differences when comparing side-to-side values of contractile characteristics in a small amount of the muscle groups tested. However, passive measurements of a relaxed muscle do not seem to fully reflect possible adaptation and changes derived from gameplay in young tennis players.

Sex differences in shoulder performance fatiguability are affected by arm position, dominance and muscle group

Background

Injury prevalence data, muscle strength, and fatiguability differ between males and females. In addition, arm spatial orientation affects muscle activation and strength of the shoulder muscles. Nevertheless, little research has been conducted in relation to the shoulder rotator muscles comparing men and women. Therefore, the main aim of of this study was to perform a comparative investigation between two arm spatial orientations (45° and 90° of abduction in the frontal plane) during a fatigue assessment of the internal rotator (IR) and external rotator (ER) shoulder muscles. Secondly, the interaction between sex and dominance with muscular performance was assessed.

Methods

Forty healthy sedentary participants, 20 males and 20 females took part in this study. Participants performed a fatigue resistance protocol consisting of 30 consecutive maximal concentric contractions of the IR and ER shoulder muscles in a supine position at a speed of 180°/s. The upper limb was abducted to an angle of 45° or 90° in the frontal plane and each participant was tested on the dominant and nom-dominant side, counterbalanced in order of administration. Performance measures of Induced Fatigue (IF; %), Cumulated Performance (C.Perf; J) and Best Repetition (BR; J) were calculated and used for analysis. IF represents the % difference between the amount of work done over the last 3 and first 3 repetitions, BR represents the largest amount of work done during a single contraction, and C.Perf represents the total amount of work done during all repetitions.

Results

Muscle group was the only factor to display significant variation when not considering other factors, with higher values for C.Perf (mean difference = 353.59 J, P < 0.0005), BR (mean difference = 14.21 J, P < 0.0005) and IF (mean difference = 3.65%, P = 0.0046). There was a significant difference between both angles, with higher values observed at 90° compared to 45° of abduction for C.Perf by ~ 7.5% (mean difference = 75 to 152 J) and ~ 10.8% (mean difference = 5.1 to 9.4 J) for BR in the ER, in males and females respectively (P < 0.0005). The dominant arm was significantly stronger than the non-dominant arm for C.Perf by 11.7% (mean difference = 111.58 J) for males and by 18% (mean difference = 82.77 J) for females in the ER at 45° abduction. At 90° abduction, only females were stronger in the dominant arm by 18.8% (mean difference = 88.17 J). Values for BR ranged from 9.2 to 21.8% depending on the abduction angle and sex of the athlete (mean difference = 2.44 – 4.85 J). Males were significantly stronger than females by 48.8 to 50.7% for values of C.Perf and BR in both the IR and ER (P < 0.0005). There was a significant difference between the ER and IR muscles, with significantly higher values observed for the IR in C.Perf (mean difference = 331.74 J) by 30.0% and in BR (mean difference = 13.31 J) by 26.64%.

Discussion

Differences in shoulder performance fatiguability between sexes are affected by arm position, arm dominance and muscle groups. In agreement with the literature, performance values in males were approximately 50% higher than in females. However, the amount of IF was no different between both sexes. Based on findings in literature, it could be suggested that this is due to differences between males and females in motor control and/or coordination strategies during repetitive tasks. In addition, we also observed the IR muscles to be significantly stronger than the ER muscles. It has long been established in literature that these observations are due to the muscle-size differences between both muscle groups, where the IR muscles can produce a larger amount of force due to the larger cross-sectional area. Results of our study found similar ER:IR ratios compared to previous reports.

Conclusion

Therefore, these findings are useful for clinicians when monitoring rehabilitation programs in sedentary individuals following shoulder injuries.

Three Simulated Goalball Games in the Same Day Cause Central Fatigue and Can Impair Game Technical Performance

The purpose of this study was to investigate the effects of three simulated goalball games on neuromuscular, physiological, perceptual, and technical parameters. Ten male players underwent assessments before and immediately after each game. Heart rate was recorded at rest and during all games that were entirely filmed for further technical performance analysis. Exercise significantly decreased knee extensor muscles peak force and percentage of voluntary activation after the second and third games, indicating the presence of central fatigue. Heart rate responses remained predominantly in a range equivalent to moderate activity intensity in all games. In addition, perceptual parameters were associated with reduced frequency of throws and density of actions. These findings suggest significant implications for the management of physical training, game strategy during a competition, and fixture change from three to two games per day.

Effects of integrative neuromuscular training intervention on physical performance in elite female table tennis players: A randomized controlled trial

Objectives

To investigate the effects of integrative neuromuscular training (INT) on physical performance in elite female table tennis players.

Methods

Twenty-four Chinese elite female table tennis players were randomized into either INT (n = 12) group or control group (CON; n = 12). INT group performed four INT sessions every week for 8 weeks, while CON group performed traditional physical fitness training. One repetition maximal (1RM), vertical jump, Y balance test and 30-meter sprinting performance were tested before and after intervention.

Results

No between groups differences were detected for any tests before intervention. Significant group by time (before or after intervention) interaction effects were observed in 1RM, vertical jump, bilateral lower limb reaching distance at posteromedial and posterolateral directions, and right leg at the anterior direction for the Y balance test (all p < 0.05), but not for the left leg at the anterior direction or the 30-meter sprinting performance (both p > 0.05). Post-hoc analysis for measurements with significant interactions revealed that all significant changes were at the ING group (all p < 0.05), while no changes for the CON group were observed (all p > 0.05).

Conclusion

Eight weeks INT significantly improved strength, power and balance in Chinese elite female table tennis players. Adopting INT in table tennis players may improve their physical performance and lead to better sports performance.

A Systematic Review of EMG Applications for the Characterization of Forearm and Hand Muscle Activity during Activities of Daily Living: Results, Challenges, and Open Issues

The role of the hand is crucial for the performance of activities of daily living, thereby ensuring a full and autonomous life. Its motion is controlled by a complex musculoskeletal system of approximately 38 muscles. Therefore, measuring and interpreting the muscle activation signals that drive hand motion is of great importance in many scientific domains, such as neuroscience, rehabilitation, physiotherapy, robotics, prosthetics, and biomechanics. Electromyography (EMG) can be used to carry out the neuromuscular characterization, but it is cumbersome because of the complexity of the musculoskeletal system of the forearm and hand. This paper reviews the main studies in which EMG has been applied to characterize the muscle activity of the forearm and hand during activities of daily living, with special attention to muscle synergies, which are thought to be used by the nervous system to simplify the control of the numerous muscles by actuating them in task-relevant subgroups. The state of the art of the current results are presented, which may help to guide and foster progress in many scientific domains. Furthermore, the most important challenges and open issues are identified in order to achieve a better understanding of human hand behavior, improve rehabilitation protocols, more intuitive control of prostheses, and more realistic biomechanical models.

Within-Session Sequence of the Tennis Serve Training in Youth Elite Players

The influence of muscular fatigue on tennis serve performance within regular training sessions is unclear. Therefore, the aim of the present study was to examine the within-session sequence of the tennis serve in youth tennis. Twenty-five young male (14.9 ± 0.9 years) and female (14.5 ± 0.9 years) players participated in this within-subject crossover study, and they were randomly but sex-matched assigned to different training sequences (serve exercise before tennis training (BTS) or after tennis training (ATS)). Pre- and post-tests included serve velocity performance and accuracy, shoulder strength, and range-of-motion (ROM) performance (internal/external rotation). Results showed that after one week of serve training conducted following the ATS sequence, significant decreases were found in serve performance (e.g., speed and accuracy), with standardized differences ranging from d = 0.29 to 1.13, as well as the shoulder function (strength [d = 0.20 to 1.0] and ROM [d = 0.17 to 0.31]) in both female and male players, compared to the BTS sequence. Based on the present findings, it appears more effective to implement serve training before the regular tennis training in youth players. If applied after training, excessive levels of fatigue may cause shoulder imbalances that could be related to an increased injury risk.

The correlation between stroke characteristics and stroke effect of young table tennis players

BACKGROUND

An optimal stroke is essential for winning table tennis competition. The main purpose of this study was to examine the correlations between the stroke characteristics and the stroke effect.

METHODS

Forty-two young table tennis players were randomly selected from China Table Tennis College (M<inf>age=</inf>14.21; M<inf>height=</inf>1.57m; M<inf>weight=</inf>46.05 kg, right-hand racket, shake-hands grip, no injuries in each joint of the body). The high-speed infrared motion capture system was used to collect the data of stroke characteristics, and the high-speed camera was used to measure the spin speed of the stroke. The influence of stroke characteristics on stroke effect was analyzed.

RESULTS

The time duration of backswing and forward motion were significantly correlated with ball speed (r=-0.403, P<0.01; r=-0.390, P<0.01, respectively) and spin speed (r=-0.244, P=0.027; r=-0.369, P<0.01, respectively). The ball speed was positively correlated with the linear velocity of right wrist joint (r=0.298, P<0.01), and the angular velocity of right elbow joint (r=0.219, P=0.013), right hip joint (r=0.427, P<0.01) and right ankle joint (r=0.443, P<0.01). The spin speed was positively correlated with the linear velocity of right wrist joint (r=0.238, P=0.031), and the angular velocity of right elbow joint (r=0.172, P=0.048) and right hip joint (r=0.277, P=0.012). The placement had a negative correlation with the angular velocity of right knee joint (r=-0.246, P=0.026).

CONCLUSIONS

The time allocation of the three phases of backspin forehand stroke had an important correlation with stroke effect, especially the ball speed and spin speed. The movement of the right wrist joint and right ankle joint were mainly correlated with the ball speed of the stroke. The spin speed of the stroke was mainly correlated with the movement of the right wrist joint. The placement of the stroke was mainly correlated with the rotation of the right knee joint.

Resistance Training Acutely Impairs Agility and Spike-Specific Performance Measures in Collegiate Female Volleyball Players Returning from the Off-Season

This study examined the acute effects of resistance training (RT) on volleyball-specific performance. Sixteen female volleyball players undertook their initial, pre-season RT bout. Countermovement jump (CMJ), delayed onset of muscle soreness (DOMS), and sport-specific performances (i.e., run-up jump, agility, and spiking speed and accuracy) were measured before, 24 (T24), and 48 (T48) hours after RT. A significant increase in DOMS was observed at T24 and T48 (~207.6% ± 119.3%; p < 0.05; ES = 1.8 (95% CI: 0.94–2.57)), whilst agility was significantly impaired at T48 (1.7% ± 2.5%; p < 0.05; ES = 0.30 (95% CI: −0.99–0.40)). However, there were no differences in CMJ (~−2.21% ± 7.6%; p > 0.05; ES = −0.11 (95% CI: −0.80–0.58)) and run-up jump (~−1.4% ± 4.7%; p > 0.05; ES = −0.07 (95% CI: −0.76–0.63)). Spiking speed was significantly reduced (−3.5% ± 4.4%; p < 0.05; ES = −0.28 (95% CI: −0.43–0.97)), although accuracy was improved (38.3% ± 81.4%: p < 0.05) at T48. Thus, the initial, preseason RT bout compromised agility and spiking speed for several days post-exercise. Conversely, spiking accuracy improved, suggesting a speed–accuracy trade-off. Nonetheless, at least a 48-h recovery may be necessary after the initial RT bout for athletes returning from the off-season or injury.

Impaired Performance of the Smash Stroke in Badminton Induced by Muscle Fatigue

PURPOSE

To evaluate the effects of muscle fatigue on badminton performance during a smash stroke.

METHODS

In total, 17 young, well-trained players completed 20 forehand smashes twice (prefatigue and postfatigue protocol), and both speed and precision of the strokes were measured. The fatigue protocol consisted of 10 series of 10 maximal countermovement jumps (3-s rest in between) followed by 8 lunges. Perception of effort and countermovement-jump performance during each series were also measured to assess fatigue.

RESULTS

Shuttlecock speed decreased moderately (-3.3%) but significantly after the fatigue protocol (P < .001, ηp2=.671). Precision significantly decreased after the fatigue protocol (-10.3%, P = .001, ηp2=.473). The decrease in precision was mainly due to an increased number of faults (P = .006, ηp2=.378, dz = 0.756) and to a decrease in accuracy (P = .066, ηp2=.195, dz = 0.478).

CONCLUSION

The present study showed that fatigue impairs performance during specific badminton skills. Moreover, by showing a slight decrease in speed and a large decrease in accuracy of the shuttlecock when fatigue is experienced, the present study suggested that, as previously observed in other racket sports, the speed of the missile appears to be the key factor used by the players to win the rally. Coaches and physical trainers should therefore develop interventions aiming to limit the negative impact of fatigue on badminton strokes.

Effect of Fatigue Protocols on Upper Extremity Neuromuscular Function and Implications for Ulnar Collateral Ligament Injury Prevention

Background

As the incidence of overuse injuries to the medial elbow in overhead athletes continues to rise, recent evidence suggests a link between these injuries and alterations in biomechanics produced by athlete fatigue. Previous studies have evaluated the effect of fatigue on elbow injuries using a wide array of fatigue protocols/athletic tasks, and, as a consequence, the results have been heterogeneous.

Purpose

To determine whether there is a uniform alteration in neuromuscular function or biomechanics as the overhead athlete fatigues. Furthermore, this study sought to determine whether player fatigue should be accounted for in ulnar collateral ligament (UCL) injury prevention programs.

Study Design

Systematic review.

Methods

A systematic review of the literature using PubMed and MEDLINE databases was performed. Keywords included fatigue, upper extremity, baseball, pitcher, throwing, and muscle activity. Inclusion criteria consisted of original research articles in the English language involving healthy athletes, use of fatigue protocols, and the evaluation of at least 1 upper limb biomechanical variable.

Results

A total of 35 studies involving 644 athletes (90 females, 554 males; mean age, 20.2 years) met the inclusion criteria. General fatigue protocols were used in 2 investigations, peripheral protocols were used in all 35 studies, and 5 different athletic tasks were studied (simulated baseball game, overhead throwing, high-effort swimming, simulated tennis game, and overhead serving). There was a uniform decrease in muscle force production and proprioception in athletes after completing a fatigue protocol. However, there was no consistency among studies when evaluating other important upper limb biomechanical factors. The fatigue protocols did not consistently produce statistically significant changes in elbow torque, pitching biomechanics, or ball velocity.

Conclusion

A uniform decrease in muscle force production and proprioception was found after fatigue protocols; however, a majority of fatigue protocols published in the current literature are inconsistently measured and produce heterogeneous results. Therefore, currently, no recommendations can be made for changes in UCL injury prevention training programs to account for potential effects of fatigue. The effect of muscle force production and proprioception on upper extremity injuries should be evaluated in future studies.

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.

Skill level and forearm muscle fatigue effects on ball speed in tennis serve

This study determined the effect of skill level (ITN 3 vs. ITN 8) on the tennis serve biomechanics and analysed the impact of forearm fatigue on dominant arm mechanisms between the two groups (expert vs. non-expert tennis players). The motion capture system with 17 reflective markers attached on anatomic landmarks of the participant was used for data collection. A total of 12 expert and 11 non-expert tennis players performed the required serving tasks. The ball speed of the expert group was significantly faster than that of the non-expert group during non-fatigued and fatigued states (p < 0.001). The wrist radial/ulnar deviation angle at impact was significantly different between non-fatigued and fatigued states for top-spin (p = 0.030) and flat serves (p = 0.018). A significant increase in extensor carpi ulnaris (ECU) and extensor carpi radialis (ECR) muscle activity during extension (p < 0.010) was observed, with that of the ECU being an ulnar deviation. Both the ECU and ECR might contribute to wrist joint and racket handle stability for the coming acceleration and impact while fatigue occurs. Fatigue might substantially influence non-experts' dominant forearms because of the significantly different elbow joint angles and dominant arm syndromes they displayed as compared with the experts.

Forearm muscle activation, ulnar nerve at the elbow and forearm fatigue in overhand sports

This study examined the morphologic changes of the ulnar nerve in different elbow positions by ultrasonography and the effects of fatigue on forearm muscle control during overhand movements. We enrolled 12 tennis players who performed flat serves and 15 baseball pitchers who performed fastball pitching. The motion capture was conducted with 14 reflective markers attached on anatomic landmarks of the participant for tennis serve and baseball pitching data collection. The distance from the nerve to the medial condyle between the tennis players and baseball pitchers showed significant differences (p = 0.006) as the elbow flexed to 90°. The differences are due to the baseball player's repetitive pitching motion while such motion does not apply to tennis player. Activity of the extensor carpi radialis (ECR) during the cocking phase in the tennis serves showed significant differences (p = 0.022) between the nonfatigued and fatigued states; the maximal value was observed in the fatigued state. The significant increase in the ECR activity in the fatigued state might be responsible for grasp-and-release activities and maintaining the wrist joint stability when performing overhand movements. Forearm fatigue influenced their overhand motion ability in accurate ball control, although it did not decrease the ball speed.

Differences within Elite Female Tennis Players during an Incremental Field Test

PURPOSE

To compare technical and physiological responses between junior and professional female players during an incremental field test to exhaustion specific to tennis.

METHODS

Twenty-seven female players (n = 14 and 13 for juniors and professionals, respectively) completed an incremental field test to exhaustion specific to tennis, which consisted of hitting alternatively forehand and backhand strokes at increasing ball frequency (ball machine) every minute. Ball accuracy and ball velocity were determined by radar and video analysis for each stroke, in addition to cardiorespiratory responses (portable gas analyzer).

RESULTS

The stage corresponding to the second ventilatory threshold (+20.0%, P = 0.027), time to exhaustion (+18.9%, P = 0.002) and maximum oxygen uptake (+12.4%, P = 0.007) were higher in professionals than in juniors. The relative percentage of maximal HR was lower at both the first (-4.7%, P = 0.014) and the second (-1.3%, P = 0.018) ventilatory thresholds in professionals. Backhand ball velocity was the only technical parameter that displayed larger (+7.1%, P = 0.016) values in professionals.

CONCLUSIONS

Compared with juniors, female professional tennis players possess higher exercise capacity, maximal and submaximal aerobic attributes along with faster backhand stroke velocities during an incremental field test specific to tennis.

Effect of Heart rate on Basketball Three-Point Shot Accuracy

The three-point shot (3S) is a fundamental basketball skill used frequently during a game, and is often a main determinant of the final result. The aim of the study was to investigate the effect of different metabolic conditions, in terms of heart rates, on 3S accuracy (3S%) in 24 male (Under 17) basketball players (age 16.3 ± 0.6 yrs). 3S performance was specifically investigated at different heart rates. All sessions consisted of 10 consecutive 3Ss from five different significant field spots just beyond the FIBA three-point line, i.e., about 7 m from the basket (two counter-clockwise “laps”) at different heart rates: rest (0HR), after warm-up (50%HRMAX [50HR]), and heart rate corresponding to 80% of its maximum value (80%HRMAX [80HR]). We found that 50HR does not significantly decrease 3S% (−15%, P = 0.255), while 80HR significantly does when compared to 0HR (−28%, P = 0.007). Given that 50HR does not decrease 3S% compared to 0HR, we believe that no preliminary warm-up is needed before entering a game in order to specifically achieve a high 3S%. Furthermore, 3S training should be performed in conditions of moderate-to-high fatigued state so that a high 3S% can be maintained during game-play.

Nonequivalent modulation of corticospinal excitability by positive and negative outcomes

OBJECTIVE

The difference between positive and negative outcomes is important in trial-and-error decision-making processes and affects corticospinal excitability. This study investigated corticospinal excitability during the performance of trial-and-error decision-making tasks with varying competing behavioral outcomes.

METHODS

Each trial began with one of five colored circles presented as a cue. Each color represented a different reward probability, ranging from 10% to 90%. The subjects were instructed to decide whether to perform wrist flexion in response to the cue. Two seconds after the presentation of the cue, a reward stimulus (picture of a coin) or penalty stimulus (mauve circle) was randomly presented to the subject. If the picture of a coin appeared, the subjects received the coin after the experiment if they had performed wrist flexion, but not if they had not performed wrist flexion. If a mauve circle appeared, a coin was deducted from the total reward if the subjects had performed wrist flexion, but not if they had not performed wrist flexion. One second after the reward or penalty stimulus, transcranial magnetic stimulation was delivered to the primary motor cortex at the midpoint between the centers of gravity of the flexor carpi radialis (agonist) and extensor carpi radialis (antagonist) muscles.

RESULTS

Cumulative wrist flexions were positively correlated with reward probabilities. Motor evoked potential (MEP) amplitudes in agonist muscles were significantly higher when wrist flexion incurred a penalty than when it incurred a reward, but there was no difference in the MEP amplitudes of antagonist muscles.

CONCLUSION

Positive and negative behavioral outcomes differentially altered behavior and corticospinal excitability, and unexpected penalties had a stronger effect on corticospinal excitability for agonist muscles.

Technical Alterations during an Incremental Field Test in Elite Male Tennis Players

PURPOSE

We investigated technical and physiological responses along with their relationships during an incremental field test to exhaustion specific to tennis (TEST) in elite players.

METHODS

Twenty male elite tennis players completed TEST, which consisted of hitting alternatively forehand and backhand strokes at increasing ball frequency (ball machine) every minute. Ball accuracy (BA), ball velocity (BV), and tennis performance (TP) index (TP = BA × BV) were determined by radar and video analysis for each stroke, in addition to cardiorespiratory responses and blood lactate concentrations.

RESULTS

At low intensities (less than 80% of maximal oxygen uptake [V˙O2max]), technical performance was steady. From 80% to 100% of V˙O2max, significant and steady decreases in BV (-9.0% and -13.3%; P = 0.02 and P = 0.002), BA (-19.4% and -18.4%; both P < 0.001), and TP (-27.4% and -29.15%; both P = 0.002) occurred for forehands and backhands, respectively. Changes in TP and blood lactate concentration from 60% to 100% of V˙O2max were inversely correlated (r = -0.51, P = 0.008). BV was 5.2% higher (P = 0.042) for forehand versus backhand, and there was no difference between strokes for both BA (P = 0.930) and TP (P = 0.536).

CONCLUSION

Technical alterations (i.e., decrease in BV, BA, and TP) in elite players undergoing TEST only occurred at high intensity (>80% of V˙O2max), presumably because of the use of compensatory strategies to overcome fatigue. Above this intensity, all technical indices decreased steadily until exhaustion, independently of the stroke nature.

Fadiga dos músculos extensores do punho diminui a força de preensão palmar

RESUMO O objetivo deste estudo foi avaliar os efeitos de um protocolo de fadiga dos músculos extensores de punho na força de preensão e da pinça lateral através da dinamometria e eletromiografia de superfície (EMG). Foram selecionados 40 indivíduos do sexo masculino, divididos em dois grupos: preensão ou pinça lateral. O protocolo de fadiga foi baseado no teste de 1 Repetição Máxima (1-RM), seguido da realização do movimento de extensão de punho repetidas vezes com carga de 75% da 1-RM. Os voluntários realizaram as tarefas de preensão ou pinça lateral associadas à dinamometria. A EMG foi realizada para ambos os grupos, analisando o comportamento, segundo o protocolo, pela frequência mediana (FM) do extensor radial do carpo (ERC), do extensor ulnar do carpo (EUC) e do flexor superficial dos dedos (FD). A dinamometria de preensão ou pinça lateral e a EMG foram realizadas antes e após o protocolo de fadiga para ambos os grupos. O protocolo de fadiga foi eficaz na diminuição da força de preensão palmar (43,5±3,85 kgf inicial e 36,50±5,1 kgf final) e da pinça lateral (10,26±1,01 kgf inicial e 8,54±0,86 kgf final), bem como na diminuição da FM, sugerindo uma condição de fadiga do EUC no grupo preensão. Os achados do presente estudo possibilitam relacionar a fadiga dos extensores de punho à diminuição de força em atividades funcionais, como a preensão, o que pode implicar em disfunções musculoesqueléticas do membro superior.

The Dutch Technical-Tactical Tennis Test (D4T) for Talent Identification and Development: Psychometric Characteristics

This study examined the test-retest reliability, validity and feasibility of the newly developed Dutch Technical-Tactical Tennis Test (D4T). This new test is relevant for talent identification and development in tennis. Thirty-two youth male tennis players (age 13.4 ± 0.5) were classified as elite (n = 15) or sub-elite (n = 17) according to their position on the national youth ranking list under 15 years (cut-off rank 50) in the Netherlands. Games, rallies and different tactical situations (i.e. offensive, neutral and defensive) were simulated with a ball machine. Players had to return 72 balls to predetermined target areas. Stroke quality was recorded based on ball velocity and accuracy (VA-index), as well as percentage errors. Test-retest reliability was assessed by comparing differences between the first and second test-session (n = 10). An intraclass-correlation coefficient of .78 for the VA-index was found (p < .05), indicating excellent test-retest reliability. Independent t-tests revealed that elite players outscored sub-elite players for the VA-index, ball velocity, accuracy and percentage errors (p < .05), supporting good validity. Furthermore, a high correlation was found between the VA-index and individual positions on the youth ranking list (p = -.75; p < .001). The assessment of feasibility indicated that the D4T was applicable for instructors and coaches. In conclusion, the D4T was shown to be a reliable, valid and feasible test to measure technical-tactical characteristics of tennis performance in youth players.

Effects of Fatigue on Throwing Performance in Experienced Team Handball Players

The purpose of this study was to investigate the effect of central and peripheral physiological fatigue on throwing accuracy and ball release velocity in team handball. Twenty male subjects (age 24.7 ± 3.9 yrs, body mass 88.5 ± 5.0 kg, body height 1.86 ± 0.05 m, training experience 12.7 ± 3.8 yrs) from one handball team participated in this study. The participants completed four sets of eight laps of a circuit that consisted of specific team handball drills/exercises, with decreasing recovery times between the laps in each set in order to induce physiological fatigue. Duration of the recovery intervals determined the description of the effort made in each set: "light" (80 s recovery between laps), "moderate" (40 s), "hard" (20 s) and "very hard" (10 s). A heart rate, concentration of lactate in blood and the rate of perceived exertion (RPE) were recorded. Ball velocity and accuracy were measured after each set and they both decreased during a fatigue protocol. However, accuracy only decreased significantly in the end of the protocol, while ball release was already affected after the first round of the protocol. The results substantiate the initial hypothesis and confirm that both throwing accuracy and ball release velocity decrease significantly as physiological fatigue increases. These variables began to decrease when the fatigue quantification values were high or very high. The findings can be used by coaches to develop training programs to teach players how to identify fatigue thresholds and combat the effects of fatigue through decision-making skills at critical game moments.

Effects of a Three-Set Tennis Match on Knee Kinematics and Leg Muscle Activation during the Tennis Serve

The purpose of this study was to determine the effect of a three-set tennis match on knee kinematics and leg muscle activation during the tennis serve in a real-time environment. Motion capture data and wireless electromyography of hamstrings and quadriceps muscles were collected from the back leg during the serve. A reduction of maximum knee flexion angle and a decrease of electromyography amplitudes in leg muscles were observed during the match. However, the knee angular velocity and the electromyography frequency of leg muscles remain unchanged throughout the match. The intermuscular compensation strategy to counteract fatigue might explain that the knee angular velocity was maintained despite reductions in knee flexion angle and electromyography activity of leg muscles.

Glenohumeral contact force during flat and topspin tennis forehand drives

The primary role of the shoulder joint in tennis forehand drive is at the expense of the loadings undergone by this joint. Nevertheless, few studies investigated glenohumeral (GH) contact forces during forehand drives. The aim of this study was to investigate GH compressive and shearing forces during the flat and topspin forehand drives in advanced tennis players. 3D kinematics of flat and topspin forehand drives of 11 advanced tennis players were recorded. The Delft Shoulder and Elbow musculoskeletal model was implemented to assess the magnitude and orientation of GH contact forces during the forehand drives. The results showed no differences in magnitude and orientation of GH contact forces between the flat and topspin forehand drives. The estimated maximal GH contact force during the forward swing phase was 3573 ± 1383 N, which was on average 1.25 times greater than during the follow-through phase, and 5.8 times greater than during the backswing phase. Regardless the phase of the forehand drive, GH contact forces pointed towards the anterior-superior part of the glenoid therefore standing for shearing forces. Knowledge of GH contact forces during real sport tasks performed at high velocity may improve the understanding of various sport-specific adaptations and causative factors for shoulder problems.

Influence of a Prolonged Tennis Match Play on Serve Biomechanics

The aim of this study was to quantify kinematic, kinetic and performance changes that occur in the serve throughout a prolonged tennis match play. Serves of eight male advanced tennis players were recorded with a motion capture system before, at mid-match, and after a 3-hour tennis match. Before and after each match, electromyographic data of 8 upper limb muscles obtained during isometric maximal voluntary contraction were compared to determine the presence of muscular fatigue. Vertical ground reaction forces, rating of perceived exertion, ball speed, and ball impact height were measured. Kinematic and upper limb kinetic variables were computed. The results show decrease in mean power frequency values for several upper limb muscles that is an indicator of local muscular fatigue. Decreases in serve ball speed, ball impact height, maximal angular velocities and an increase in rating of perceived exertion were also observed between the beginning and the end of the match. With fatigue, the majority of the upper limb joint kinetics decreases at the end of the match. No change in timing of maximal angular velocities was observed between the beginning and the end of the match. A prolonged tennis match play may induce fatigue in upper limb muscles, which decrease performance and cause changes in serve maximal angular velocities and joint kinetics. The consistency in timing of maximal angular velocities suggests that advanced tennis players are able to maintain the temporal pattern of their serve technique, in spite of the muscular fatigue development.

The neuromuscular fatigue induced by repeated scrums generates instability that can be limited by appropriate recovery

The aim of this study was to evaluate the influence of the fatigue on the machine scrum pushing sagittal forces during repeated scrums and to determine the origin of the knee extensor fatigue. Twelve elite U23 rugby union front row players performed six 6-s scrums every 30 s against a dynamic scrum machine with passive or active recovery. The peak, average, and the standard deviation of the force were measured. A neuromuscular testing procedure of the knee extensors was carried out before and immediately after the repeated scrum protocol including maximal voluntary force, evoked force, and voluntary activation. The average and peak forces did not decrease after six scrums with passive recovery. The standard deviation of the force increased by 70.2 ± 42.7% (P < 0.001). Maximal voluntary/evoked force and voluntary activation decreased (respectively 25.1 ± 7.0%, 14.6 ± 5.5%, and 24 ± 9.9%; P < 0.001). The standard deviation of the force did not increase with active recovery and was associated with lower decrease of maximal voluntary/evoked force and voluntary activation (respectively 12.8 ± 7.9%, 4.9 ± 6.5%, and 7.6 ± 4.1%; all P < 0.01). As a conclusion repeated scrummaging induced an increased machine scrum pushing instability associated with central and peripheral fatigue of the knee extensors. Active recovery seems to limit all these manifestations of fatigue.

Playing vs. nonplaying aerobic training in tennis: physiological and performance outcomes

This study compared the effects of playing and nonplaying high intensity intermittent training (HIIT) on physiological demands and tennis stroke performance in young tennis players. Eleven competitive male players (13.4 ± 1.3 years) completed both a playing and nonplaying HIIT session of equal distance, in random order. During each HIIT session, heart rate (HR), blood lactate, and ratings of perceived exertion (RPE) were monitored. Before and after each HIIT session, the velocity and accuracy of the serve, and forehand and backhand strokes were evaluated. The results demonstrated that both HIIT sessions achieved an average HR greater than 90% HRmax. The physiological demands (average HR) were greater during the playing session compared to the nonplaying session, despite similar lactate concentrations and a lower RPE. The results also indicate a reduction in shot velocity after both HIIT sessions; however, the playing HIIT session had a more deleterious effect on stroke accuracy. These findings suggest that 1) both HIIT sessions may be sufficient to develop maximal aerobic power, 2) playing HIIT sessions provide a greater physiological demand with a lower RPE, and 3) playing HIIT has a greater deleterious effect on stroke performance, and in particular on the accuracy component of the ground stroke performance, and should be incorporated appropriately into a periodization program in young male tennis players.

Metabolic optimisation of the basketball free throw

The free throw (FT) is a fundamental basketball skill used frequently during a match. Most of actual play occurs at about 85% of maximum heart rate (HR). Metabolic intensity, through fatigue, may influence a technically skilled move as the FT is. Twenty-eight under 17 basketball players were studied while shooting FTs on a regular indoor basketball court. We investigated FT accuracy in young male basketball players shooting at three different HRs: at rest, at 50% and at 80% of maximum experimentally obtained HR value. We found no significant FT percentage difference between rest and 50% of the maximum HR (FT percentage about 80%; P > 0.05). Differently, at 80% of the maximum HR the FT percentage decreased significantly by more than 20% (P < 0.001) down to about 60%. No preliminary warm-up is needed before entering game for the FT accuracy. Furthermore, we speculate that time-consuming, cooling-off routines usually performed by shooters before each FT may be functional to improve its accuracy.

Effects of sports drinks on the maintenance of physical performance during 3 tennis matches: a randomized controlled study

Background

Tennis tournaments often involve playing several consecutive matches interspersed with short periods of recovery.

Objective

The objective of this study was firstly to assess the impact of several successive tennis matches on the physical performance of competitive players and secondly to evaluate the potential of sports drinks to minimize the fatigue induced by repeated matches.

Methods

This was a crossover, randomized controlled study. Eight male regionally-ranked tennis players participated in this study. Players underwent a series of physical tests to assess their strength, speed, power and endurance following the completion of three tennis matches each of two hours duration played over three consecutive half-days (1.5 day period for each condition). In the first condition the players consumed a sports drink before, during and after each match; in the second, they drank an identical volume of placebo water. The results obtained were compared with the third ‘rest’ condition in which the subjects did not play any tennis. Main outcomes measured were maximal isometric strength and fatigability of knee and elbow extensors, 20-m sprint speed, jumping height, specific repeated sprint ability test and hand grip strength.

Results

The physical test results for the lower limbs showed no significant differences between the three conditions. Conversely, on the upper limbs the EMG data showed greater fatigue of the triceps brachii in the placebo condition compared to the rest condition, while the ingestion of sports drinks attenuated this fatigue.

Conclusions

This study has demonstrated for the first time that, when tennis players are adequately hydrated and ingest balanced meals between matches, then no large drop in physical performance is observed even during consecutive competitive matches.

Trial registration

ClinicalTrials.gov: NCT01353872.

Motor cortex-evoked activity in reciprocal muscles is modulated by reward probability

Horizontal intracortical projections for agonist and antagonist muscles exist in the primary motor cortex (M1), and reward may induce a reinforcement of transmission efficiency of intracortical circuits. We investigated reward-induced change in M1 excitability for agonist and antagonist muscles. Participants were 8 healthy volunteers. Probabilistic reward tasks comprised 3 conditions of 30 trials each: 30 trials contained 10% reward, 30 trials contained 50% reward, and 30 trials contained 90% reward. Each trial began with a cue (red fixation cross), followed by blue circle for 1 s. The subjects were instructed to perform wrist flexion and press a button with the dorsal aspect of middle finger phalanx as quickly as possible in response to disappearance of the blue circle without looking at their hand or the button. Two seconds after the button press, reward/non-reward stimulus was randomly presented for 2-s duration. The reward stimulus was a picture of Japanese 10-yen coin, and each subject received monetary reward at the end of experiment. Subjects were not informed of the reward probabilities. We delivered transcranial magnetic stimulation of the left M1 at the midpoint between center of gravities of agonist flexor carpi radialis (FCR) and antagonist extensor carpi radialis (ECR) muscles at 2 s after the red fixation cross and 1 s after the reward/non-reward stimuli. Relative motor evoked potential (MEP) amplitudes at 2 s after the red fixation cross were significantly higher for 10% reward probability than for 90% reward probability, whereas relative MEP amplitudes at 1 s after reward/non-reward stimuli were significantly higher for 90% reward probability than for 10% and 50% reward probabilities. These results implied that reward could affect the horizontal intracortical projections in M1 for agonist and antagonist muscles, and M1 excitability including the reward-related circuit before and after reward stimulus could be differently altered by reward probability.