Plantar Flexor Muscle Activity and Fascicle Behavior in Gastrocnemius Medialis During Running in Highly Cushioned Shoes With Carbon-Fiber Plates.

The purposes of this study were to clarify the electromyography (EMG) of plantar flexors and to analyze the fascicle and tendon behaviors of the gastrocnemius medialis (GM) during running in the carbon-fiber plate embedded in thicker midsole racing shoes, such as the Nike ZoomX Vaporfly (VF) and traditional racing shoes (TRAD). We compared the fascicle and series elastic element behavior of the GM and EMG of the lower limb muscles during running (14 km/h, 45 s) in athletes wearing VF or TRAD. GM EMGs in the push-off phase were approximately 50% lower in athletes wearing VF than in TRAD. Although the series elastic element behavior and/or mean fascicle-shortening velocity during the entire stance phase were not significantly different between VF and TRAD, a significant difference was found in both the mean EMG and integral EMG of the GM during the push-off phase. EMG of the gastrocnemius lateralis (GL) during the first half of the push-off phase was significantly different between VF and TRAD. Present results suggest that VF facilitates running propulsion, resulting in a decrease in GM and GL EMGs at a given running velocity during the push-off phase, leading to a reduction in metabolic cost.

Martial arts training is related to implicit intermanual transfer of visuomotor adaptation.

Recent work identified an explicit and implicit transfer of sensorimotor adaptation with one limb to the other, untrained limb. Here, we pursue the idea that different individual factors contribute differently to the amount of explicit and implicit intermanual transfer. In particular, we tested a group of judo athletes who show enhanced right-hemispheric involvement in motor control and a group of equally trained athletes. After adaptation to a 60° visual rotation, we estimated awareness of the perturbation and transfer to the untrained, non-dominant left hand in two experiments. We measured the total amount of intermanual transfer (explicit plus implicit) by telling the participants to repeat what was learned during adaptation, and the amount of implicit transfer by instructing the participants to refrain from using what was learned and to perform movements as during baseline instead. We found no difference between the total intermanual transfer of judokas and running experts, with mean absolute transfer values of 42.4° and 47.0°. Implicit intermanual transfer was very limited, but larger in judokas than in general sports athletes, with mean values of 5.2° and 1.6°. A multiple linear regression analysis further revealed that total intermanual transfer, which mainly represents the explicit transfer, is related to awareness of the perturbation, while implicit intermanual transfer can be predicted by judo training, amount of total training, speed of adaptation, and handedness scores. The findings suggest that neuronal mechanisms such as hemispheric interactions and functional specialization underlying intermanual transfer of motor learning may be applied according to individual predisposition.

Comparison of the Position-Matching and Position-Reproducing Tasks to Detect Deficits in Knee Position Sense After Reconstruction of the Anterior Cruciate Ligament.

CONTEXT: Deficits in knee position sense following reconstruction of the anterior cruciate ligament (ACL) can delay an athlete's return to sport participation and increase the risk of reinjury. Deficits in position sense postreconstruction have been evaluated using either a position-reproducing or position-matching task. OBJECTIVE: The aim of our study was to combine both to determine which assessment would be more effective to identify deficits in knee position sense. DESIGN: Longitudinal laboratory-based study. PARTICIPANTS: Eleven athletes (6 men and 5 women; mean age, 20.5 [1.2] y), who had undergone ACL reconstruction with an ipsilateral hamstring autograft, and 12 age-matched controls. INTERVENTIONS: Position sense was evaluated at 6 and 12 months postreconstruction and once for the control group. In addition, peak isokinetic knee extension and flexion strength, at 60°/s and 180°/s, was assessed for the ACL reconstruction group to evaluate possible influences of muscle strength on knee joint position sense. MAIN OUTCOME MEASURES: The variables include the angular differences between the reference limb and indicator limb, and peak torque values of isokinetic knee extension and flexion. RESULTS: Significant matching differences were identified at 6 months postsurgery on the position-matching task, but not at 12 months postsurgery. No significant between-group and within-subject differences were identified on the position-reproducing task. No significant matching errors were identified for the control group. There was no correlation between errors in position sense and maximum isokinetic strength. CONCLUSION: The position-matching task is more sensitive than the position-reproducing task to identify deficits in knee position sense over the first year following ACL reconstruction surgery.

Effect of salient points in movements on the constraints in bimanual coordination.

The relative-salience hypothesis has been proposed as a possible explanation for the stability of bimanual coordination. This explanation proceeds from a psychological viewpoint and is based on the following tenets: (1) cyclic joint motions involving two movements are conceived of as a unified event, (2) if a "single" point in each movement is seen as the most salient, the salient points of the two movements prefer to go together, and (3) in other cases, a unified event will be constrained by movement direction. In this investigation, we examined whether the relative-salience hypothesis could predict the type of constraint (i.e., action coupling vs movement direction) for various bimanual coordination movements. Participants performed six different joint movements in synchrony with metronome beats. Both index finger flexion/extension and forearm pronation/supination had a "single" salient point (JMsingleSP), the others had "two" salient points (JMtwoSP). Then, we applied the relative-salience hypothesis to four bimanual coordinations. The coupling of simultaneous forearm pronation was more stable than alternate pronation. Similarly, the coupling of finger flexion and forearm pronation was more stable than that of finger flexion and forearm supination. For the coordination of radial flexion/ulnar flexion and index finger flexion/extension as well as forearm pronation/supination and radial flexion/ulnar flexion, symmetric movements were more stable than asymmetric movements. The results indicated that the stability of bimanual coordination was predominantly constrained by coupling of salient points when using two JMsingleSP and it was predominantly constrained by movement direction when coordinating JMsingleSP and JMtwoSP. Thus, the relative-salience hypothesis was supported.

Performance control in one consecutive motor task sequence - Αpproaching central neuronal motor behaviour preceding isometric contraction onsets and relaxation offsets at lower distinct torques.

OBJECTIVE: Motor-related cortical potentials (MRCP) often compared separated muscle activations; however, MRCP preceding combined contraction onsets and relaxation offsets of one consecutive motor task sequence remain to be elucidated. METHODS: Twelve healthy males (27.92±4.33 years, 181.83±7.15 cm, 84.58±7.15 kg) performed 40 submaximal isometric right-limb wrist flexions (i.e. motor task sequences). Each motor task sequence combined timed contractions to and relaxations from distinct torque levels, i.e. 20% and 40% of maximum voluntary contractions (MVC). Synchronized continuous EEG (32 Ag/AgCl-electrodes mounted over motor-related areas) and EMG (i.e. flexor carpi radialis, FCR) recordings served to detect torque level-on/offsets for MRCP analyses. RESULTS: Motor task sequences were accurately maintained with participants' mean values of FCR muscle activity revealing no signs of fatigue (p⟩0.05). Main findings (i.e. readiness potential) were larger amplitudes over frontal electrode sites (p⟨0.05) preceding contractions compared to relaxations, whereas amplitudes were larger (i.e. peak) over centro-parietal electrode sites (p⟨0.05) preceding 40% compared to 20% MVC. CONCLUSION: When performed in one consecutive motor task sequence, controlling the production as well as the releasing of force may require similar proprioceptive and visuo-motor processing preceding the same force level (i.e. 20% or 40%); however, this is irrespective of the muscle activation type (i.e. contraction or relaxation).

Neural basis for the relationship between frequency of going outdoors and depressive mood in older adults.

OBJECTIVE: Low frequency of going outdoors (e.g. being homebound) is associated with depressive mood; however, the underlying neural mechanism of this association is unclear. We therefore investigated the neural substrate involved in the relationship between frequency of going outdoors and depressive mood using positron emission tomography (PET), focusing on the frontal lobe and the limbic system. METHODS: One hundred fifty-eight community-dwelling older adults aged 65-85 years underwent PET with 18 F-fluorodeoxyglucose to evaluate regional cerebral metabolic rates of glucose normalized in reference to cerebellar glucose metabolic value (normalized-rCMRglc) in six regions of interest. We also assessed depressive mood, frequency of going outdoors, and potential covariates. Depressive mood was assessed using the Geriatric Depression Scale (GDS). RESULTS: The proportion of participants who reported low frequency of going outdoors (LG, every 2-3 days or less) was 36.1%. The LG group showed significantly higher GDS scores than those who reported high (once a day or more) frequency of going outdoors. A multiple linear regression analysis adjusted for potential covariates showed higher GDS scores were associated with lower normalized-rCMRglc in the ventrolateral prefrontal and orbitofrontal cortices. Adjusting for frequency of going outdoors, the association between GDS score and normalized-rCMRglc in the orbitofrontal cortex was attenuated. CONCLUSIONS: Our results suggest that the orbitofrontal cortex may mediate the relationship between low frequency of going outdoors and depressive mood among community-dwelling older adults. These findings may help disentangle the role of going outdoors in regulating brain function to improve and/or maintain mental health among community-dwelling older adults. Copyright © 2016 John Wiley & Sons, Ltd.

Relation Between Lift Force and Ball Spin for Different Baseball Pitches.

Although the lift force (F(L)) on a spinning baseball has been analyzed in previous studies, no study has analyzed such forces over a wide variety of spins. The purpose of this study was to describe the relationship between F(L) and spin for different types of pitches thrown by collegiate pitchers. Four high-speed video cameras were used to record flight trajectory and spin for 7 types of pitches. A total of 75 pitches were analyzed. The linear kinematics of the ball was determined at 0.008-s intervals during the flight, and the resultant fluid force acting on the ball was calculated with an inverse dynamics approach. The initial angular velocity of the ball was determined using a custom-made apparatus. Equations were derived to estimate the F(L) using the effective spin parameter (ESp), which is a spin parameter calculated using a component of angular velocity of the ball with the exception of the gyro-component. The results indicate that F(L) could be accurately explained from ESp and also that seam orientation (4-seam or 2-seam) did not produce a uniform effect on estimating F(L) from ESp.

Mode-dependent control of human walking and running as revealed by split-belt locomotor adaptation.

Here, we investigate the association of neural control between walking and running, and in particular, how these two gait modes at different velocities are controlled by the central nervous system. The subjects were fully adapted by acquiring modified motor patterns to either walk or run on a split-belt treadmill driven in split mode (asymmetry in the velocities of two belts at 1.0 and 2.0 m s(-1)). Subsequently, we tested how the adaptation affected walking and running at three different velocities in the tied mode (equal belt velocities). At 0.75 m s(-1), we found a preference to walk, at 1.50 m s(-1), there was a preference to both walk and run, and at a velocity of 2.25 m s(-1) there was a preference to run. Both walking and running on the split belt resulted in the emergence of a significant aftereffect (asymmetrical movement) at all of the velocities tested when walking after adapting to walk and running after adapting to run. However, for contrasting modes (i.e. running after adapting to walk and walking after adapting to run), such aftereffects were far less evident at all velocities; thus showing only limited transfer across gait modes. The results demonstrate a clear mode dependency in the neural control of human walking and running. In addition, only for walking, was there a degree of velocity dependency.

Estimation of the core temperature control during ambient temperature changes and the influence of circadian rhythm and metabolic conditions in mice.

It has been speculated that the control of core temperature is modulated by physiological demands. We could not prove the modulation because we did not have a good method to evaluate the control. In the present study, the control of core temperature in mice was assessed by exposing them to various ambient temperatures (Ta), and the influence of circadian rhythm and feeding condition was evaluated. Male ICR mice (n=20) were placed in a box where Ta was increased or decreased from 27°C to 40°C or to -4°C (0.15°C/min) at 0800 and 2000 (daytime and nighttime, respectively). Intra-abdominal temperature (Tcore) was monitored by telemetry. The relationship between Tcore and Ta was assessed. The range of Ta where Tcore was relatively stable (range of normothermia, RNT) and Tcore corresponding to the RNT median (regulated Tcore) were estimated by model analysis. In fed mice, the regression slope within the RNT was smaller in the nighttime than in the daytime (0.02 and 0.06, respectively), and the regulated Tcore was higher in the nighttime than in the daytime (37.5°C and 36.0°C, respectively). In the fasted mice, the slope remained unchanged, and the regulated Tcore decreased in the nighttime (0.05 and 35.9°C, respectively), while the slopes in the daytime became greater (0.13). Without the estimating individual thermoregulatory response such as metabolic heat production and skin vasodilation, the analysis of the Ta-Tcore relationship could describe the character of the core temperature control. The present results show that the character of the system changes depending on time of day and feeding conditions.

Interaction between simultaneous contraction and relaxation in different limbs.

We investigated the interaction between relaxation and contraction for remote, ipsilateral muscles of the hand and foot (wrist extensor/ankle dorsiflexor). Subjects sat in an armchair and were able to freely move their right hand and foot. They performed eight tasks: (1) wrist extension from a flexed (relaxed) position, (2) ankle dorsiflexion from a plantarflexed (relaxed) position, (3) wrist relaxation from an extended position, (4) ankle relaxation from a moderately dorsiflexed position. The remaining tasks involved (5) simultaneous performance of tasks 1 and 2, (6) 3 and 4, (7) 1 and 4, and (8) 2 and 3. Subjects performed each task as fast as possible after hearing a start signal. They were instructed not to activate antagonistic muscles in the tasks involving relaxation. When contraction of the wrist flexor/ankle dorsiflexor was concurrent with relaxation of the ipsilateral limb (ankle dorsiflexor/wrist extensor), the reaction time of contraction as observed in electromyography (EMG) activities in the wrist extensor/ankle dorsiflexor became longer and the EMG activities became smaller. Our findings suggest that muscle relaxation in one limb interferes with smooth movement of muscle contraction in the ipsilateral limb.

Reciprocal inhibition of the thigh muscles in humans: A study using transcutaneous spinal cord stimulation.

Evaluating reciprocal inhibition of the thigh muscles is important to investigate the neural circuits of locomotor behaviors. However, measurements of reciprocal inhibition of thigh muscles using spinal reflex, such as H-reflex, have never been systematically established owing to methodological limitations. The present study aimed to clarify the existence of reciprocal inhibition in the thigh muscles using transcutaneous spinal cord stimulation (tSCS). Twenty able-bodied male individuals were enrolled. We evoked spinal reflex from the biceps femoris muscle (BF) by tSCS on the lumber posterior root. We examined whether the tSCS-evoked BF reflex was reciprocally inhibited by the following conditionings: (1) single-pulse electrical stimulation on the femoral nerve innervating the rectus femoris muscle (RF) at various inter-stimulus intervals in the resting condition; (2) voluntary contraction of the RF; and (3) vibration stimulus on the RF. The BF reflex was significantly inhibited when the conditioning electrical stimulation was delivered at 10 and 20 ms prior to tSCS, during voluntary contraction of the RF, and during vibration on the RF. These data suggested a piece of evidence of the existence of reciprocal inhibition from the RF to the BF muscle in humans and highlighted the utility of methods for evaluating reciprocal inhibition of the thigh muscles using tSCS.

Modulation of corticospinal excitability dependent upon imagined force level.

Motor imagery is defined as the mental execution of a movement without any muscle activity. In the present study, corticospinal excitability was assessed by motor evoked potentials (MEPs) when the subjects imagined isometric elbow flexion at various force levels. Electromyography was recorded from the right brachioradialis, the biceps brachii and the triceps brachii muscles. First, the maximum voluntary contraction (MVC) of elbow flexion was recorded in each subject. Subjects practiced performing 10, 30 and 60 % MVC using visual feedback. After the practice, MEPs were recorded during the imagery of elbow flexion with the forces of 10, 30 and 60 % MVC without any feedback. After the MEPs recording, we assigned subjects to reproduce the actual elbow flexion force at 10, 30 and 60 % MVC. The MEPs amplitudes in the brachioradialis and biceps brachii in the 60 % MVC condition were significantly greater than those in the 10 % MVC condition (p < 0.05). These findings suggest that the enhancement of corticospinal excitability during motor imagery is associated with an increase in imagined force level.

Relative importance of different surface regions for thermal comfort in humans.

In a previous study, we investigated the contribution of the surface of the face, chest, abdomen, and thigh to thermal comfort by applying local temperature stimulation during whole-body exposure to mild heat or cold. In hot conditions, humans prefer a cool face, and in cold they prefer a warm abdomen. In this study, we extended investigation of regional differences in thermal comfort to the neck, hand, soles, abdomen (Experiment 1), the upper and lower back, upper arm, and abdomen (Experiment 2). The methodology was similar to that used in the previous study. To compare the results of each experiment, we utilized the abdomen as the reference area in these experiments. Thermal comfort feelings were not particularly strong for the limbs and extremities, in spite of the fact that changes in skin temperature induced by local temperature stimulation of the limbs and extremities were always larger than changes that were induced in the more proximal body parts. For the trunk areas, a significant difference in thermal comfort was not observed among the abdomen, and upper and lower back. An exception involved local cooling during whole-body mild cold exposure, wherein the most dominant preference was for a warmer temperature of the abdomen. As for the neck and abdomen, clear differences were observed during local cooling, while no significant difference was observed during local warming. We combined the results for the current and the previous study, and characterized regional differences in thermal comfort and thermal preference for the whole-body surface.

Electromyographic analysis of lower limbs during baseball batting.

We investigated the muscle activation pattern of lower limbs in baseball batting by recording surface electromyography (sEMG) from 8 muscles, the left and right rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and medial gastrocnemius (MG) muscles. The muscle activities were compared between 10 skilled baseball players and 10 unskilled novices. The batting motion was divided into 7 phases: waiting, shifting body weight, stepping, landing, swing, impact, and follow through. The timing for these phases was analyzed by using a high-speed video camera. The onset latencies of sEMG were significantly earlier in baseball players at the left-RF (p < 0.01), right-BF (p < 0.05), and left-BF (p < 0.01). The peak amplitudes of sEMG activity were greater in skilled players at the right-RF (p < 0.01), right-BF (p < 0.01), left-BF (p < 0.01), left-TA (p < 0.01), right-MG (p < 0.01), and left-MG (p < 0.05). The timing for shifting, stepping, and landing was also significantly earlier in skilled players (p < 0.05, p < 0.01, and p < 0.05, respectively). Our findings suggest that preparations for the swing are made earlier in skilled baseball players who recruit their lower muscles for the swing more effectively than novices.

Relationship between performance variables and baseball ability in youth baseball players.

The present study investigated the relationship of performance variables and anthropometric measurements on baseball ability in 164 youth baseball players (age: 6.4-15.7 years). To evaluate their baseball performance, ball speeds in pitching and batting were recorded and kinetic energies of the pitched and hit balls were calculated. To record anthropometric and physical fitness characteristics, height and weight were measured and a battery of physical fitness tests covering standing long jump, side steps, sit-ups, 10-m sprint, trunk flexion, back strength, and grip strengths of both hands were conducted. The results of a multiple regression analysis revealed several significant predictors: age, body mass index (BMI), standing long jump, 10-m sprint, and grip strength for pitched ball kinetic energy and age, BMI, standing long jump, and back strength for hit ball kinetic energy. This study provides scientific evidence that relates certain specific physical performance tests and body characteristics with high achievement in the actual performance of pitching and batting. Youth players, their parents, coaches, and trainers would benefit by addressing these characteristics when planning training programs to improve the baseball performance of youth players.

Effect of hopping frequency on bilateral differences in leg stiffness.

Understanding the degree of leg stiffness during human movement would provide important information that may be used for injury prevention. In the current study, we investigated bilateral differences in leg stiffness during one-legged hopping. Ten male participants performed one-legged hopping in place, matching metronome beats at 1.5, 2.2, and 3.0 Hz. Based on a spring-mass model, we calculated leg stiffness, which is defined as the ratio of maximal ground reaction force to maximum center of mass displacement at the middle of the stance phase, measured from vertical ground reaction force. In all hopping frequency settings, there was no significant difference in leg stiffness between legs. Although not statistically significant, asymmetry was the greatest at 1.5 Hz, followed by 2.2 and 3.0 Hz for all dependent variables. Furthermore, the number of subjects with an asymmetry greater than the 10% criterion was larger at 1.5 Hz than those at 2.2 and 3.0 Hz. These results will assist in the formulation of treatment-specific training regimes and rehabilitation programs for lower extremity injuries.

The effect of fastball backspin rate on baseball hitting accuracy.

The effectiveness of fastballs of equivalent speed can differ; for example, one element of this difference could be due to the effect of rate and orientation of ball spin on launched ball trajectory. In the present experiment, baseball batters' accuracy in hitting fastballs with different backspin rates at a constant ball velocity of 36 m/s was examined. Thirteen skilled baseball players (professionals, semiprofessionals, and college varsity players) participated in the study. The movements of bat and ball were recorded using two synchronized high-speed video cameras. The Pearson product-moment correlation coefficient (r) was calculated and used to analyze the relationship between ball backspin rate and the vertical distance between ball center and sweet spot at the moment of ball-bat impact. Ball backspin rate was positively correlated with increases in the distance from the optimal contact point of the swung bat (sweet spot) to the actual point of contact (r = .38, P < .001). Batters were most effective at the usual backspin rate for the ball velocity used. The decrease in accuracy of the batter's swing that was observed when the fastball's backspin deviated from the usual rate likely occurred because experienced batters predict ball trajectory from perceived ball speed.

Disturbance in hitting accuracy by professional and collegiate baseball players due to intentional change of target position.

The present study investigated bat control of skilled baseball batters during tee batting, faced with an intentional change in target position. Twelve, skilled, male baseball players (M age = 24 yr., SD = 4) participated in the study. Participants were instructed to hit a baseball off a tee 0.8 m from the ground (Hitting condition), and also to deliberately swing just above the ball (Air Swing condition). The task for the participants was to perform, in alternate order, 15 swings at a real baseball on a stationary tee and 15 swings at an imaginary ball that was said to be on top of the real baseball. The participants were instructed to hit the ball toward center field just as they would hit in a game. While most participants could hit the real ball in the sweet area of the bat, only one participant did so in the Air Swing condition. Average distances from the center of the sweet area to ball center at the moment of ball-bat contact in the Air Swing condition (85 mm) were significantly greater than the distance in the Hitting condition (38 mm). The larger error in hitting an imaginary ball in the sweet area could be due to perceptual changes following the batter's altered focus, expectation of a lack of contact, and/or lack of feedback from the swing. It was suggested that baseball batters should be aware of the possible error in hitting accurately when they intentionally shifted the target.

Constraints on hand-foot coordination associated with phase dependent modulation of corticospinal excitability during motor imagery.

Interlimb coordination involving cyclical movements of hand and foot in the sagittal plane is more difficult when the limbs move in opposite directions compared with the same direction (directional constraint). Here we first investigated whether the directional constraint on hand-foot coordination exists in motor imagery (imagined motion). Participants performed 10 cyclic coordinated movements of right wrist flexion-extension and right ankle dorsiflexion-plantarflexion as quickly and precisely as possible, in the following three conditions; (1) actual movements of the two limbs, (2) imaginary movements of the two limbs, and (3) actual movement of one limb combined with imaginary movement of the other limb. Each condition was performed under two directions; the same and the opposite direction. Task execution duration was measured as the time between the first and second press of a button by the participants. The opposite directional movement took a significantly longer time than did the same directional movement, irrespective of the condition type. This suggests that directional constraint of hand-foot coordination occurs even in motor imagery without actual motor commands or kinesthetic signals. We secondarily examined whether the corticospinal excitability of wrist muscles is modulated in synchronization with an imaginary foot movement to estimate the neural basis of directional constraint on imaginary hand-foot coordination. The corticospinal excitability of the forearm extensor in resting position increased during dorsiflexion and decreased during plantarflexion similarly in both actual and imaginary foot movements. This corticospinal modulation depending on imaginary movement phase likely produces the directional constraint on the imaginary hand-foot coordination.

Interlimb and Intralimb Coordination of Rectus Femoris and Biceps Femoris Muscles at Different Running Speeds.

PURPOSE: The purpose of this study was to investigate the relationship between spatiotemporal variables and the muscle activity of the rectus femoris (RF) and biceps femoris (BF) in both legs at various running speeds. METHODS: Eighteen well-trained male athletes (age: 20.7 ± 1.8 yr) were asked to run for 50 m with 7 different "subjective efforts (SE)" (20%, 40%, 60%, 80%, 90%, 95%, and 100% SE). SE scaled relative to the maximal effort running (100%). The spatiotemporal variables (running speed, step frequency, step length) were measured over the distance from 30 to 50 m. The RF and BF muscle activities were obtained from both legs with wireless electromyography (EMG) sensors. We calculated RF and BF onset/offset timings in both legs (e.g., ipsilateral leg RF is "iRF," contralateral leg BF is "cBF"), which were expressed as % of a running cycle. Based on those timings, we obtained the EMG timing variables (%), as Switch1 (iBF offset to iRF onset), Switch2 (iRF offset to iBF onset), Scissors1 (cBF onset to iRF onset), and Scissors2 (iRF offset to cBF offset). RESULTS: running speed was well correlated with the SE, and higher running speed (>9 m·s -1 ) was achieved with higher step frequency (>4.0 Hz). Relative timings of RF and BF onset/offset (%) appeared earlier and later, respectively, with an increase in running speed. The absolute duration of RF activation (s) was elongated with the decrease in absolute running cycle time (increase in running speed). Both Switch and Scissors showed significant negative correlations with running speed and step frequency. CONCLUSIONS: The RF and BF excitation in both legs, as evidenced by changes in both Switch and Scissors, is coordinated for controlling running speed, as well as step frequency.