Rate of Torque Development and Feedforward Control of the Hip and Knee Extensors: Gender Differences

Reliability of a method to assess corticomotor excitability of lower limb muscles using a normalized EMG motor thresholding procedure

Given the importance of determining intervention-induced neuroplastic changes with lower extremity functional tasks, a reliable transcranial magnetic stimulation (TMS) methodology for proximal lower extremity muscles is needed. A pre-set fixed voltage value is typically used as the criterion for identifying a motor evoked potential (MEP) during the motor thresholding procedure. However, the fixed voltage value becomes problematic when the procedure is applied to proximal lower extremity muscles where active contractions are required. We sought to establish the reliability of a method measuring corticomotor excitability of gluteus maximus and vastus lateralis using normalized electromyography (EMG) as the criterion for identifying MEPs during the motor thresholding procedure. The active motor threshold for each muscle was determined using the lowest stimulator intensity required to elicit 5 MEPs that exceeded 20% maximal voluntary isometric contraction from 10 stimulations. TMS data were obtained from 10 participants on 2 separate days and compared using random-effect intra-class correlation coefficients (ICCs). Slopes from two input-output curve fitting methods as well as the maximum MEP of gluteus maximus and vastus lateralis were found to exhibit good to excellent reliability (ICCs ranging from 0.75 to 0.99). The described TMS method using EMG-normalized criteria for motor thresholding produced reliable results utilizing a relatively low number of TMS pulses.

Kinetics of Depth Jumps Performed by Female and Male National Collegiate Athletics Association Basketball Athletes and Young Adults

The depth jump (DJ) is commonly used to evaluate athletic ability, and has further application in rehabilitation and injury prevention. There is limited research exploring sex-based differences in DJ ground reaction force (GRF) measures. This study aimed to evaluate for sex-based differences in DJ GRF measures and determine sample size thresholds for binary classification of sex. Forty-seven participants from mixed-sex samples of NCAA athletes and young adults performed DJs from various drop heights. Force platform dynamometry and 2-dimensional videography were used to estimate GRF measures. Three-way mixed analysis of variance was used to evaluate main effects and interactions. Receiver operating characteristic (ROC) curve analysis was used to evaluate the combined sensitivity and specificity of dependent measures to sex. Results revealed that reactive strength index scores and rebound jump heights were greater in males than females (p < 0.001). Additionally, young adult females showed greater peak force reduction than young adult males (p = 0.002). ROC curve analysis revealed mixed results that appeared to be influenced by population characteristics and drop height. In conclusion, sex-based differences in DJ performance were observed, and the results of this study provide direction for future DJ investigations.

Electromyographic differences of the gluteus maximus, gluteus medius, biceps femoris, and vastus lateralis between the barbell hip thrust and barbell glute bridge

Hip extensor muscles are critical to sport performance as events requiring sprinting and forceful landings are highly dependent on these muscles. Despite biomechanical differences between the barbell hip thrust (BHT) and the barbell glute bridge (BGB), both are biomechanically efficient ways to load this musculature for training purposes. Research investigating the differences in muscular activity between the BHT and BGB has yet been conducted. The aim of this study was to investigate, through surface electromyography, if one exercise is more optimal than the other in producing greater muscle activation for specific hip extensor muscles. Ten male participants completed a two-part study protocol. Results revealed the BHT elicited significantly greater muscle activity within the vastus lateralis for peak and mean outcomes; however, the BGB elicited significantly greater muscle activity in the upper and lower gluteus maximus for peak and mean outcomes and mean outcome in the gluteus medius. Current findings suggest, the BGB is, at minimum, a superior substitute for the BHT for eliciting a larger magnitude of activity in the gluteus maximus. Future studies between the two exercises are warranted to discern which produces greater hypertrophy and whether adaption of the BHT or BGB transfers more optimally to sport performance.

Hip Abductor Rate of Torque Development as Opposed to Isometric Strength Predicts Peak Knee Valgus During Landing: Implications for Anterior Cruciate Ligament Injury

Peak knee valgus has been shown to predict anterior cruciate ligament injury. The purpose of the current study was to compare peak rate of torque development (RTD) to peak isometric torque as a predictor of peak knee valgus during landing. Twenty-three healthy females participated. Hip abductor muscle performance was quantified using 2 types of isometric contractions: sustained and rapid. Peak isometric torque was calculated from the sustained isometric contraction. Peak RTD was calculated from the rapid isometric contraction (0-50 and 0-200 ms after force initiation). Kinematic data were collected during the deceleration phase of a double-leg drop jump task. Linear regression was used to assess the ability of hip abductor muscle performance variables to predict peak knee valgus. Increased peak RTD during the 0 to 50 milliseconds window after force initiation was found to significantly predict lower peak knee valgus (P = .011, R2 = .32). In contrast, neither peak RTD from 0 to 200 milliseconds after force initiation window (P = .45, R2 = .03) nor peak isometric torque (P = .49, R2 = .03) predicted peak knee valgus. The inability of the hip abductors to rapidly generate muscular force may be more indicative of "at-risk" movement behavior in females than measures of maximum strength.

Corticomotor excitability of gluteus maximus and hip extensor strength: The influence of sex

PURPOSE

To compare hip extensor strength and corticomotor excitability (CME) of gluteus maximus (GM) between males and females. A secondary purpose was to determine if CME of GM is predictive of hip extensor strength.

METHOD

Thirty-two healthy individuals participated (15 males and 17 females). CME of GM was assessed using the input-output curve (IOC) procedure acquired from transcranial magnetic stimulation (average slope). Hip extensor strength was measured by a dynamometer during a maximal voluntary isometric contraction. Independent t-tests were used to compare CME of GM and peak hip extensor torque between males and females. Linear regression analysis was used to determine whether peak hip extensor torque was predicted by CME of GM.

RESULT

Compared to males, females demonstrate lower peak hip extensor torque (4.42 ± 1.11 vs. 6.15 ± 1.72 Nm/kg/m2, p < 0.01) and lower CME of GM (1.36 ± 1.07 vs. 2.67 ± 1.30, p < 0.01). CME of GM was a significant predictor of peak hip extensor torque for males and females combined (r² = 0.36, p < 0.001).

CONCLUSION

Our findings support the premise that corticomotor excitability plays a role in the ability of a muscle to generate torque.

Improvements in Hip Extensor Rate of Torque Development Influence Hip and Knee Extensor Feed-Forward Control

Females have been reported to utilize a feedforward control strategy during landing in which they compensate for decreased rate of torque development (RTD) of the hip extensors through earlier pre-activation of the knee extensors. The purpose of this study was to determine the influence of a 4-week hip-focused training program on hip extensor RTD and feedforward control of the hip and knee extensors. Twenty-one females underwent hip extensor RTD evaluation and electromyographic assessment of the hip and knee extensors during a drop-jump task. Post-training, there was a significant improvement in hip extensor RTD (21.68 ± 5.44 to 23.33 ± 5.45 Nm/kg s, p = 0.009), and pre-activation of the hip extensors (87.1 ± 63.6 to 56.2 ± 60.9 ms, p < 0.001) and knee extensors (272.3 ± 113.8 to 124.0 ± 67.7 ms, p < 0.001) occurred closer to ground contact. A negative association was found between the change in hip extensor RTD and the change in knee extensor onset (r = -0.48, p = 0.03). We propose that the observed change in feedforward control is reflective of the decreased need for preparatory muscle activity owing to the improved capacity of the hip extensors to rapidly generate force.

Neuromuscular Strategies in Stretch-Shortening Exercises with Increasing Drop Heights: The Role of Muscle Coactivation in Leg Stiffness and Power Propulsion

When applying drop jump exercises, knowing the magnitude of the stimulus is fundamental to stabilize the leg joints and to generate movements with the highest power. The effects of different drop heights on leg muscles coactivation, leg stiffness and power propulsion were investigated in fifteen sport science students. Drop jumps from heights of 20, 30, 40, 50, and 60 cm in a random order were performed on a force platform. During each drop jump, the ground reaction force, knee angle displacement, and synchronized surface-electromyography root-mean-square (sEMG_RMS) activity (vastus lateralis, VL; vastus medialis, VM; rectus femoris, RF; biceps femoris, BF; tibialis anterior, TA and lateral gastrocnemius, LG) were recorded. The coactivation in the pre-contact phase, between VL and BF, VM and BF as well as RF and BF, was dependent on the drop height (p < 0.01; effect size (ES) ranged from 0.45 to 0.90). Leg stiffness was dependent on the drop height (p < 0.001; ES = 0.27-0.28) and was modulated by the coactivation of VM-BF (p = 0.034) and RF-BF (p = 0.046) during the braking phase. Power propulsion was also dependent on the drop height (p < 0.001; ES = 0.34); however, it was primarily modulated by the coactivation of LG-TA during the braking phase (p = 0.002). The coactivation of thigh muscles explains leg stiffness adjustments at different drop heights. On the contrary, the coactivation of shank muscles is mostly responsible for the power propulsion.

Corticomotor Excitability of Gluteus Maximus Is Associated with Hip Biomechanics During a Single-Leg Drop-Jump

The purpose of this study was to determine the association between corticomotor excitability (CME) of gluteus maximus (GM) and hip biomechanics during a single-leg drop-jump task. Thirty-two healthy individuals participated. The slope of the input-output curve (IOC) obtained from transcranial magnetic stimulation was used to assess CME of GM. The average hip extensor moment and peak hip flexion angle during the stance phase of the drop jump task was calculated. The slope of the IOC of GM was found to be a predictor of the average hip extensor moment (r² = 0.18, p = 0.016) and peak hip flexion angle (r² = 0.20, p = 0.01). Our results demonstrate that greater functional use of the hip was associated with enhanced descending neural drive of GM.