High‐density electromyography activity in various hamstring exercises

Proximal‐distal differences in muscle activity are rarely considered when defining the activity level of hamstring muscles. The aim of this study was to determine the inter‐muscular and proximal‐distal electromyography (EMG) activity patterns of hamstring muscles during common hamstring exercises. Nineteen amateur athletes without a history of hamstring injury performed 9 exercises, while EMG activity was recorded along the biceps femoris long head (BFlh) and semitendinosus (ST) muscles using 15‐channel high‐density electromyography (HD‐EMG) electrodes. EMG activity levels normalized to those of a maximal voluntary isometric contraction (%MVIC) were determined for the eccentric and concentric phase of each exercise and compared between different muscles and regions (proximal, middle, distal) within each muscle. Straight‐knee bridge, upright hip extension, and leg curls exhibited the highest hamstrings activity in both the eccentric (40%‐54%MVIC) and concentric phases (69%‐85%MVIC). Hip extension was the only BF‐dominant exercise (Cohen's d = 0.28 (eccentric) and 0.33 (concentric)). Within ST, lower distal than middle/proximal activity was found in the bent‐knee bridge and leg curl exercises (d range = 0.53‐1.20), which was not evident in other exercises. BFlh also displayed large regional differences across exercises (d range = 0.00‐1.28). This study demonstrates that inter‐muscular and proximal‐distal activity patterns are exercise‐dependent, and in some exercises are affected by the contraction mode. Knowledge of activity levels and relative activity of hamstring muscles in different exercises may assist exercise selection in hamstring injury management.     

Muscle activation during lower body resistance training

This study evaluated the biceps femoris (BF), rectus femoris (RF), and vastus lateralis (VL) activation and activation ratios of a variety of resistance training exercises characterized by knee extension, and determined if subject strength or gender affects these variables. The exercises evaluated included the leg extension, squat, deadlift, lunge, and step up. Subjects included 20 athletes and recreationally active college students. Electromyography (EMG) of the muscles expressed as a percentage of maximum voluntary isometric contraction (MVIC), as well as the BF to RF and BF to VL EMG ratio, were determined for each exercise. There was no significant interaction between gender and exercise type for the RMS EMG of the BF (p = 0.67), RF (p = 0.53), or VL (p = 0.06). Main effects were found for the RMS EMG of the BF (p = 0.00), RF (p = 0.00), and VL (p = 0.00), as well as the RMS EMG of the BF to RF activation ratio (p = 0.00) and BF to VL activation ratios (p = 0.003), between exercises. Peak RMS EMG was also assessed. Post hoc analysis identified specific differences in muscle activation and ratios between exercises. Clinicians should consider the magnitude of muscle activation and activation ratios when prescribing hamstring and quadriceps exercises.     

Medial hamstring muscle activation patterns are affected 1–6 years after ACL reconstruction using hamstring autograft

Purpose

Although changes in hamstring muscle morphology after anterior cruciate ligament reconstruction (ACLR) using a semitendinosus autograft hamstrings-gracilis (HG) of the ipsilateral limb are recognized, alterations in muscle activation patterns have not been extensively studied. The purpose of this controlled laboratory trial was therefore to monitor muscle activation levels of the medial (MH) and lateral (LH) hamstring muscles in athletes who had undergone ACLR using a HG autograft and to contrast these to activation levels demonstrated by healthy controls.

Methods

Surface electromyography (EMG) was sampled from bilateral hamstring muscles of 18 athletes 1–6 years after ACLR and 18 matched controls (CTRL) during the performance of two dissimilar exercises, both involving eccentric knee flexor activity. Peak normalized muscle activation levels were identified for MH and LH of both limbs during the performance of the Nordic Hamstring (NH) exercise and TRX^® hamstring curl (TRX) exercise.

Results

A statistically significant limb by exercise interaction was found for peak activation levels of LH, due to significant interlimb differences in activation during the performance of the TRX exercise compared to more symmetrical activation during the NH (p < 0.001). A three-way interaction was found for peak activation levels of MH, due to group differences in peak muscle activation between limbs and exercise type (p = 0.025). Whereas CTRL group participants consistently favoured one limb over the other during the performance of both exercises, ACLR participants demonstrated dissimilar peak MH activation patterns between limbs during the performance of the NH exercise compared to the TRX.

Conclusions

In light of these results and considering the surgical procedure, patients who undergo ACLR using a HG autograft from the ipsilateral limb may benefit from post-operative rehabilitation that involves muscle activation and strengthening specifically targeting the MH component.     

Region‐dependent hamstrings activity in Nordic hamstring exercise and stiff‐leg deadlift defined with high‐density electromyography

Recent studies suggest region‐specific metabolic activity in hamstring muscles during injury prevention exercises, but the neural representation of this phenomenon is unknown. The aim of this study was to examine whether regional differences are evident in the activity of biceps femoris long head (BFlh) and semitendinosus (ST) muscles during two common injury prevention exercises. Twelve male participants without a history of hamstring injury performed the Nordic hamstring exercise (NHE) and stiff‐leg deadlift (SDL) while BFlh and ST activities were recorded with high‐density electromyography (HD‐EMG). Normalized activity was calculated from the distal, middle, and proximal regions in the eccentric phase of each exercise. In NHE, ST overall activity was substantially higher than in BFlh (d  =  1.06 ± 0.45), compared to trivial differences between muscles in SDL (d  =  0.19 ± 0.34). Regional differences were found in NHE for both muscles, with different proximal‐distal patterns: The distal region showed the lowest activity level in ST (regional differences, d range = 0.55‐1.41) but the highest activity level in BFlh (regional differences, d range = 0.38‐1.25). In SDL, regional differences were smaller in both muscles (d range = 0.29‐0.67 and 0.16‐0.63 in ST and BFlh, respectively) than in NHE. The use of HD‐EMG in hamstrings revealed heterogeneous hamstrings activity during typical injury prevention exercises. High‐density EMG might be useful in future studies to provide a comprehensive overview of hamstring muscle activity in other exercises and high‐injury risk tasks.     

Trunk muscle activity during spine stabilization exercises performed in a pool

ObjectivesTo compare trunk muscle activity levels among a variety of therapeutic aquatic exercises designed for patients with low back pain.Study designQuantitative observational laboratory study.SettingSports medicine clinic housed in a University.ParticipantsEleven physically active males aged 25.7 ± 5.53 years.Main outcome measuresSurface electromyographic (EMG) data from muscles rectus abdominis (RA), external oblique (EO), lower abdominals (LA), multifidus (MT), and erector spinae (ES) were recorded and then normalized to a maximal voluntary contraction.ResultsEMG values during abdominal bracing and Swiss ball exercises for muscles RA, EO, LA, and ES were significantly greater than most other exercises tested that included pelvic tilt, marching, hip abduction, and alternating arm exercises (P = .04–.001). EMG values of muscle LA were also greater for the abdominal hollowing exercise, whereas muscle MT displayed the greatest EMG values during the hip abduction exercise when compared to most other exercises tested (P = .02–.001).ConclusionsThe aquatic exercises that maximize trunk muscle activity in the healthy males studied are abdominal bracing and Swiss ball exercises. Some muscles were selectively activated during abdominal hollowing (LA) and hip abduction (MT) exercises when compared to most other exercises.     

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

ObjectivesThe 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.DesignObservational study.SettingUniversity laboratory.Participants32 healthy university students (male/female: 14/18) volunteers.Main outcome measuresSubjects 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.ResultsIncreased 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.ConclusionsThe 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.     

肌电生物反馈训练对膝关节损伤后某些肌肉功能的影响

对40名男性受试者为时7周的训练表明,对膝关节损伤后进行康复训练,在肌力增长上,肌电生物反馈训练优于非肌电反馈训练(P<0.05)。     

Comparison of gluteus maximus and hamstring electromyographic activity and lumbopelvic motion during three different prone hip extension exercises in healthy volunteers

ObjectiveTo compare the surface electromyography (EMG) amplitude of the hip joint, including the gluteus maximus (GM), biceps femoris (BF), and semitendinosus (ST) muscles generated by three different exercises: prone hip extension (PHE), prone table hip extension (PTHE), and prone table hip extension with 90° knee flexion (PTHEK), with compensatory pelvic motions.DesignRepeated-measure within-subject intervention.ParticipantsSixteen-healthy males (mean age = 23.4 ± 2.2 years).Main outcome measuresEMG was used to collect EMG signals from the GM, erector spinae (ES), BF, and ST muscles. Furthermore an electromagnetic tracking motion analysis was also performed to measure the compensations.ResultsEMG amplitude differed significantly among the three conditions (PHE vs. PTHE vs. PTHEK) (p < 0.05). The mean GM muscle activity increased significantly during the PTHEK (70.93% and 13.75% increases in %MVIC compared with the PHE and PTHE, respectively) (p < 0.01). However, there was no significant difference in the kinematic data for rotation or anterior tilting angle of the pelvis among the three conditions (p > 0.05).ConclusionsThese results suggest that the PTHEK can be recommended as an effective method to strengthen the GM muscle without increased BF or ES muscle activities and without compensatory pelvic motions.     

Does fatigue induced by repeated dynamic efforts affect hamstring muscle function?

PURPOSE: The purpose of this study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running. METHODS: Twelve subjects performed three maximal 40-m sprints during which time high-speed film of the subjects' sprint action and EMG of five lower extremity muscles were recorded (nonfatigued condition, NFC). Subjects then performed specific and general hamstring fatigue tasks followed by three final 40-m sprints (fatigued condition, FC) during which time high-speed film and EMG of the same muscles were again recorded. RESULTS: Statistical analysis of the kinematic data indicated the following significant (P < 0.05) changes in the subjects' running action from the NFC to the FC: decreased hip and knee flexion at maximum knee extension in the swing phase of the sprint cycle, decreased leg angular velocity immediately before foot-ground contact (FGC), and decreased angular displacement of the trunk, thigh, and leg segments during the late swing phase. Statistical analysis of the EMG data indicated a significant increase in the duration of hamstring activity and earlier cessation of rectus femoris activity during the swing phase of the sprint stride. CONCLUSIONS: It was concluded that these changes in the kinematic and EMG parameters of sprint running primarily served as protective mechanisms to reduce stress placed on the hamstring muscles at critical phases of the stride cycle.     

Quadriceps EMG/force relationship in knee extension and leg press

PURPOSE: This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg press (LP) exercises. METHODS: Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF). RESULTS: There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads. CONCLUSIONS: The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.     

Muscle recruitment during plyometric exercises in overhead athletes with and without shoulder pain

ObjectivesTo investigate if there is a difference in muscle activity patterns during high load plyometric shoulder exercises between overhead athletes with and without shoulder pain.DesignControlled laboratory EMG study.SettingUniversity EMG Laboratory.ParticipantsSixty overhead athletes, 30 with shoulder pain and 30 healthy controls were included.Main outcome measuresThe EMG activity of Upper Trapezius (UT), Middle Trapezius (MT), Lower Trapezius (LT), Serratus Anterior (SA), Latissimus Dorsi (LD) and Pectoralis Major (PM) on the tested side and bilateral on Abdominal Obliques Externus (OE) muscles was registered with wireless surface EMG during 3 rotational plyometric shoulder exercises in 3 positions, prone, sidelying and standing.ResultsA significant higher muscle activity was found in the shoulder pain group for MT together with an overall significant higher activity in the thoraco-humeral and abdominal muscles compared to healthy controls.ConclusionsWhen rehabilitating the overhead athlete with shoulder pain, shoulder muscles together with both thoraco-humeral and abdominal muscles need to be engaged.     

The effects of ACL injury on lower extremity activation during closed kinetic chain exercise

AIM: Injury to the anterior cruciate ligament (ACL) has been suggested to alter the neuromuscular mechanism in the lower extremity. However, conclusive evidence regarding this occurrence has yet to be established during closed kinetic chain exercise. The purpose of this study was to assess differences in muscle activation during slideboard exercise between non-injured, ACL deficient, and ACL reconstructed individuals. METHODS: Experimental design: comparative study. Setting: research laboratory. Participants: subjects for this study included 10 healthy, non-injured (NI) individuals, 7 uni-lateral ACL deficient (ACLD) individuals, and 6 uni-lateral ACL reconstructed (ACLR) individuals. Interventions: EMG activity was measured from the vastus medialis (VM), vastus lateralis (VL), medial hamstring (MH), lateral hamstring (LH), tibialis anterior (TA), and medial gastrocnemius (MG) muscles during slideboard performance. Measures: EMG for each muscle during each of 6 phases of 1 average slideboard cycle was expressed as a percentage of EMG during a maximal voluntary contraction. RESULTS: The results demonstrated that during slideboard phase I the VM, VL, and TA muscles generated the greatest amount of activity as compared to the other muscles. Vastus medialis muscle activation was found to be significantly higher than the other muscles in the involved/dominant limb, as compared to the non-involved/non-dominant limb during slideboard phase II. During slideboard phases III-VI, tibialis anterior muscle activation was found to be consistently higher than the other muscles, while hamstring muscle activity was consistently the lowest. CONCLUSION: It is concluded that adaptive changes following ACL injury during a dynamic, closed kinetic chain activity such as the slideboard exercise, may be a restoration of a bi-lateral balance in muscle activation.     

Muscle activation patterns in the Nordic hamstring exercise: Impact of prior strain injury

This study aimed to determine: (a) the spatial patterns of hamstring activation during the Nordic hamstring exercise (NHE); (b) whether previously injured hamstrings display activation deficits during the NHE; and (c) whether previously injured hamstrings exhibit altered cross‐sectional area (CSA). Ten healthy, recreationally active men with a history of unilateral hamstring strain injury underwent functional magnetic resonance imaging of their thighs before and after six sets of 10 repetitions of the NHE. Transverse (T2) relaxation times of all hamstring muscles [biceps femoris long head (BFlh); biceps femoris short head (BFsh); semitendinosus (ST); semimembranosus (SM)] were measured at rest and immediately after the NHE and CSA was measured at rest. For the uninjured limb, the ST's percentage increase in T2 with exercise was 16.8%, 15.8%, and 20.2% greater than the increases exhibited by the BFlh, BFsh, and SM, respectively (P < 0.002 for all). Previously injured hamstring muscles (n = 10) displayed significantly smaller increases in T2 post‐exercise than the homonymous muscles in the uninjured contralateral limb (mean difference ?7.2%, P = 0.001). No muscles displayed significant between‐limb differences in CSA. During the NHE, the ST is preferentially activated and previously injured hamstring muscles display chronic activation deficits compared with uninjured contralateral muscles.     

EMG activation of abdominal muscles in the crunch exercise performed with different external loads

ObjectiveThe aim of this study was to describe by means of surface electromyography the activation of the rectus abdominis, obliquus externus and rectus femoris muscles during the “crunch” abdominal exercise performed with loads.MethodsThirteen subjects performed crunch exercises with loads representing 80, 60, 40 and 20% of the 1-RM (100%) in a random order with the subjects drawing lots, and with a 5 min rest between sets. Surface bipolar EMG electrodes were used. The root mean square of the EMG was calculated for the first repetition of each load. Differences between conditions were tested using a one way ANOVA for repeated measures. Post-hoc Bonferroni tests was used to detect significant differences between specific loads (p < 0.05).ResultsAn average of the percentage values of all studied abdominal muscles was used as a representative value of abdominal synergy (Ab Syn). In general it can be concluded that the abdominal muscles were significantly more recruited in the 100% load condition. Abdominal activation significantly differed between the various loads; however, in general adjacent loads (20 vs. 40% – 1-RM) did not differ.ConclusionsThese results suggest that for young, healthy and physically active adults when the objective is progression in the training process of abdominal force, the option ought to be for changes of load superior to 20% of the 1-RM.     

The uptake of the Nordic hamstring exercise programme as an injury prevention strategy in professional cricket in the United Kingdom and barriers to implementation

ObjectivesTo report hamstring prevention strategies of professional male cricket clubs in the United Kingdom, identify the application of the Nordic hamstring programme (NHP) and gain knowledge of medical teams’ reasons for the NHP’s inclusion or exclusion.DesignCross-sectional questionnaire.SettingOnline survey.Participants15 (75%) of professional cricket clubs in the United Kingdom.Main outcome measuresSurvey based on the RE-AIM framework.ResultsTwelve clubs reported having a formal hamstring injury prevention programme. The Nordic hamstring exercise and eccentric exercises (100%) were the most used interventions. Three clubs implemented the NHP, with one classed as fully compliant. Respondents partially agreed, on a 5 point Likert scale, that the Nordic hamstring exercise was effective at reducing injuries at their club (Mean 3.73 ± SD 0.70) and across professional cricket (3.87 ± 0.64). Barriers to implementation across cricket included players not positively perceiving the programme (60%) with a cultural change required (60%) for its adoption.ConclusionsThe Nordic hamstring exercise is positively received by medical personnel in professional cricket in conjunction with other prevention strategies. Three clubs have utilised the NHP in the last three seasons with one club considered fully compliant. A cultural shift from players and coaches may be required for successful NHP implementation.     

Trunk kinematics and muscle activation patterns during stand-to-sit movement and the relationship with postural stability in aging

BackgroundStand-to-sit (StandTS) movement is an important functional activity that can be challenging for older adults due to age-related changes in neuromotor control. Although trunk flexion, eccentric contraction of the rectus femoris (RF), and coordination of RF and biceps femoris (BF) muscles are important to the StandTS task, the effects of aging on these and related outcomes are not well studied.Research questionWhat are the age-related differences in trunk flexion, lower extremity muscle activation patterns, and postural stability during a StandTS task and what is the relationship between these variables?MethodsTen younger and ten older healthy adults performed three StandTS trials at self-selected speeds. Outcomes included peak amplitude, peak timing, burst duration, and onset latency of electromyography (EMG) activity of the RF and BF muscles, trunk flexion angle and angular velocity, whole body center of mass (CoM) displacement, center of pressure (CoP) velocity, and ground reaction force (GRF).ResultsThere were no age-related differences in weight-bearing symmetry, StandTS and trunk flexion angular velocity, or BF activity. In both groups, EMG peak timing of RF was preceded by BF. Compared to younger adults, older adults demonstrated shorter RF EMG burst duration, reduced trunk flexion, and reduced stability as indicated by the longer duration in which CoM was maintained beyond the posterior limit of base of support (BoS), greater mean anterior-posterior CoP velocity and larger standard deviation of CoM vertical acceleration during StandTS with smaller vertical GRF immediately prior to StandTS termination. Trunk flexion angle and RF EMG burst duration correlated with stability as measured by the duration in which the CoM stayed within the BoS.SignificanceDecreased trunk flexion and impaired eccentric control of the RF are associated with StandTS instability in aging and suggest the importance of including StandTS training as a part of a comprehensive balance intervention.     

Hamstring injury prevention in soccer: Before or after training?

We examined the effects of a 12‐week program of Nordic hamstring exercises (NHE ), administered before or after football training, upon eccentric hamstring strength, muscle activity, and architectural adaptations. Amateur soccer players were randomized into three groups. The control group (CON ; n=11) undertook core stability exercises, whereas a periodized NHE program was delivered either before (NHE_BEF ; n=10) or after (NHE_AFT ; n=14) biweekly training sessions. Outcome measures included peak torque and concomitant normalized peak surface electromyography signals (sEMG ) of the biceps femoris (BF ) and medial hamstring (MH ) muscles during knee flexor maximal eccentric contractions, performed at 30°·s⁻¹. Ultrasonography was used to determine BF muscle thickness, muscle fiber pennation angle, and fascicle length. Performing the NHE derived likely moderate peak torque increases in both NHE_BEF (+11.9%; 90% confidence interval: 3.6%‐20.9%) and NHE_AFT (+11.6%; 2.6%‐21.5%) vs CON . Maximum sEMG increases were moderately greater in the BF of both NHE training groups vs CON . There were likely moderate increases in BF muscle thickness (+0.17 cm; 0.05‐0.29 cm) and likely small pennation angle increases (+1.03°; −0.08° to 2.14°) in NHE_AFT vs CON and NHE_BEF . BF fascicle length increases were likely greater in NHE_BEF (+1.58 cm; 0.48‐2.68 cm; small effect) vs CON and NHE_AFT . A 12‐week eccentric hamstring strengthening program increased strength and sEMG to a similar magnitude irrespective of its scheduling relative to the football training session. However, architectural adaptations to support the strength gains differed according to the timing of the injury prevention program.     

30秒全力蹬踏自行车运动中下肢肌肉协同活动特征研究

目的:观察30秒全力蹬踏自行车运动中下肢肌肉表面肌电信号随运动时间变化的特征,揭示该运动过程中下肢主要用力肌肉的协同活动规律。方法:10名场地自行车运动员(男7名,女3名,年龄21.5±4.7岁)在Wattbike功率自行车上进行30秒全力蹬踏自行车运动,记录输出功率、蹬踏频率和下肢股直肌、股肌(股内侧肌、股外侧肌)、腘绳肌(股二头肌、半腱肌)、胫骨前肌、腓肠肌外侧头、比目鱼肌的表面肌电信号,并采用高速摄像机记录运动影像。基于运动影像确定蹬踏周期起止点。基于表面肌电信号获取各测试肌肉的肌电中值频率、活动水平、激活时间和三组肌肉的协同收缩比率(CAI胫骨前肌/比目鱼肌、CAI股肌/腓肠肌、CAI股肌/腘绳肌)。结果:在运动结束即刻,蹬踏频率和输出功率分别相对于最大值下降了21.51%±5.40%和56.17%±9.91%。股直肌、股肌、腓肠肌肌电幅值、激活时间和肌电中值频率随运动持续时间的增加表现出单调递减(P<0.05)。肌肉协同收缩比率CAI胫骨前肌/比目鱼肌随运动持续时间的增加单调递增,而协同收缩比率CAI股肌/腓肠肌表现出单调递减趋势(P<0.05)。结论:在30秒全力蹬踏自行车运动中,股直肌、股肌、胫骨前肌、腓肠肌都出现较深的肌肉疲劳。在此过程中,下肢肌肉的协同活动呈现非同步性的变化,引起股肌-腓肠肌动力传递效率下降和踝关节拮抗肌共收缩比率增加。     

Surface electromyography of the forearm musculature during an overhead throwing rehabilitation progression program

ObjectiveThe flexor carpi ulnaris (FCU) and flexor digitorum superficialis (FDS) provide dynamic stabilization to the medial elbow. It remains unclear how these muscles function during progressive throwing exercises. Our objective was to compare FCU and FDS surface electromyography (sEMG) during a throwing progression.DesignCrossover.SettingLaboratory.ParticipantsSixteen healthy males.Main outcome measuresParticipants completed a plyometric throw (PLYO), long-toss 50% (LT₅₀), long-toss 75% (LT₇₅), and pitch (PITCH). sEMG was synchronized with three-dimensional kinematics to assess the acceleration phase of each exercise. Peak sEMG amplitude (%MVIC) and percentage change between progressive exercises was measured. Continuous sEMG data were assessed to determine when peak activation occurred during acceleration.ResultsFCU activity was greater during PITCH than LT₅₀, and during LT₇₅ than LT₅₀. Percentage change was greater from LT₅₀-to-LT₇₅ than PLYO-to-LT₅₀ for both muscles. PLYO and PITCH increased most during late acceleration, whereas LT₅₀ and LT₇₅ increased most during mid-acceleration.ConclusionsFCU activity did not increase in a stepwise manner, and FDS remained unchanged. Each muscle demonstrated a disproportionate increase in activation during the second exercise progression (LT₅₀-to-LT₇₅) compared to the first (PLYO-to-LT₅₀), suggesting that additional exercises may be required to achieve a stepwise progression relative to forearm muscle activation.