Subsequent Swing Research Articles

Are the ground reaction forces altered by the curve and with the increasing sprinting velocity?

In 200- and 400-m races, 58% of the total distance to cover is in the curve. In the curve, the sprinting performance is decreased in comparison to the straight. However, the reasons for this decreased performance is not well understood. Thus, the aim of this study was to identify the kinetic parameters underpinning the sprinting performance in the curve in comparison to the straight. Nineteen experienced-to-elite curve specialists performed five sprints in the straight and in the curve (radius 41.58 m): 10, 15, 20, 30, and 40 m. The left and the right vertical, anterior-posterior, medial-lateral, and resultant ground reaction forces (respectively , , , and ), the associated impulses (respectively , , , and ) and thestance times of each side were averaged over each distance. In the curve, the time to cover the 40-m sprint was longer than in the straight (5.52 ± 0.25 vs. 5.47 ± 0.23 s, respectively). Additionally, the left and the right and were lower than in the straight while the left and the right increased, meaning that the was more medial. The left was also lower than in the straight while the left stance times increased to keep the left similar to the straight to maintain the subsequent swing time. Overall, the sprinting performance was reduced in the curve due to a reduction in the left and the right and , that were likely attributed to the concomitant increased to adopt a curvilinear motion.

A study on the thermodynamic characteristics of a mechanical A/C swing angle milling head

Several studies have evaluated the thermal error modeling and structural characteristics of the swing angle milling head; however, few studies have reported the thermodynamic characteristics of the swing angle milling head. Therefore, based on the thermodynamic theory, the thermodynamic characteristics of the mechanical A/C swing angle milling head of the five axis CNC gantry milling machine are evaluated, and the relevant heating calculation results are obtained. The temperature field distribution and thermodynamic characteristics of the swing angle milling head were simulated and analyzed by using ANSYS Workbench finite element software. In addition, the accuracy and rationality of the finite element simulation results of this study are verified based on the experimental conclusions of other relevant scholars that the maximum temperature of the gear is also mainly distributed near the pitch line of the tooth surface. The research results indicate that the maximum heat generation area inside the swing angle milling head is mainly concentrated on the pitch line of the bevel gear tooth surface of the main spindle execution component, with a maximum temperature of 43.559°C. The maximum thermal deformation is located at the tip of the swing angle milling head, with a maximum thermal deformation of 1.8353 × 10−5 m, this study can provide important theoretical reference and data support for the structural optimization and thermal deformation control of subsequent swing angle milling heads.

Neuromuscular adjustments to unweighted running: the increase in hamstring activity is sensitive to trait anxiety.

Introduction: Originally developed for astronauts, lower body positive pressure treadmills (LBPPTs) are increasingly being used in sports and clinical settings because they allow for unweighted running. However, the neuromuscular adjustments to unweighted running remain understudied. They would be limited for certain lower limb muscles and interindividually variable. This study investigated whether this might be related to familiarization and/or trait anxiety. Methods: Forty healthy male runners were divided into two equal groups with contrasting levels of trait anxiety (high, ANX+, n = 20 vs. low, ANX-, n = 20). They completed two 9-min runs on a LBPPT. Each included three consecutive 3-min conditions performed at 100%, 60% (unweighted running), and 100% body weight. Normal ground reaction force and electromyographic activity of 11 ipsilateral lower limb muscles were analyzed for the last 30s of each condition in both runs. Results: Unweighted running showed muscle- and stretch-shortening cycle phase-dependent neuromuscular adjustments that were repeatable across both runs. Importantly, hamstring (BF, biceps femoris; STSM, semitendinosus/semimembranosus) muscle activity increased during the braking (BF: +44 ± 18%, p < 0.001) and push-off (BF: +49 ± 12% and STSM: +123 ± 14%, p < 0.001 for both) phases, and even more so for ANX+ than for ANX-. During the braking phase, only ANX+ showed significant increases in BF (+41 ± 15%, p < 0.001) and STSM (+53 ± 27%, p < 0.001) activities. During the push-off phase, ANX+ showed a more than twofold increase in STSM activity compared to ANX- (+119 ± 10% vs. +48 ± 27, p < 0.001 for both). Conclusion: The increase in hamstring activity during the braking and push-off phases may have accelerated the subsequent swing of the free-leg, likely counteracting the unweighting-induced slowing of stride frequency. This was even more pronounced in ANX+ than in ANX-, in an increased attempt not to deviate from their preferred running pattern. These results highlight the importance of individualizing LBPPT training and rehabilitation protocols, with particular attention to individuals with weak or injured hamstrings.

Response of the Thoroughbred Forelimb to Perturbations Caused by a Change in Ground Surface

Thoroughbred racehorses are often affected by musculoskeletal injuries, leading to involuntary rest, early retirement or death. Hardness and consistency of the track surface have been implicated as major risk factors for limb injury. The purpose was to test the utility of a preliminary AnyBody musculoskeletal model of the equine forelimb for its responses on two perturbing surfaces. A musculoskeletal model was developed using CT, muscle, tendon and ligament properties, and kinematic data were applied from ridden trials using five Thoroughbred horses. Horses were ridden at trot and canter on a baseline sand surface, and through two perturbation pits containing a harder and a softer surface for one stance phase. In response to the hard perturbation, the proximal limb was more compliant at trot and canter, as measured by increased shoulder flexion in the perturbed stance phase and increased elbow and carpal flexion in the subsequent swing phase. The suspensory ligaments and muscle-tendon units were less strained while lacertus fibrosus was more strained. In response to the soft perturbation, the coffin joint was more flexed and the elbow was more extended in the acute stance phase at trot, resulting in increased strain to the DDF, extensor branches and lacertus fibrosus. At canter, the coffin was more flexed, the fetlock less hyperextended and so the suspensory structures were less strained in the perturbed stance phase, but more strained in the second stance phase. Changes in ground surface affect both the perturbed stance phase, and the following stance phase.

Young adults perceive small disturbances to their walking balance even when distracted

BackgroundThe ability to perceive disturbances to ongoing locomotion (e.g., slips and trips) may play an important role in walking balance control. However, how well young adults can perceive such disturbances is unknown. Research questionThe purpose of this study was to identify the perception threshold in young adults to subtle slip-like locomotor disturbances. MethodsSubjects (n = 12) walked on a split-belt treadmill performing a perturbation discrimination task at their preferred walking speed while randomly experiencing locomotor balance disturbances every 8–12 strides. Balance disturbances were imposed through a short-duration decrease in velocity of a single treadmill belt triggered at heel-strike. The treadmill belt returned to the subject’s preferred walking speed during the subsequent swing phase. Locomotor disturbances were given with eight different velocity changes ranging from 0 to 0.4 m/s and were randomized and repeated 5 times. Subjects were prompted to respond when asked if they perceived each disturbance. Using a psychophysical approach, we determined the perception thresholds of slip-like locomotor disturbances (i.e., just noticeable difference). The perturbation discrimination task was repeated with subjects performing a secondary cognitive distraction (counting backward by threes). ResultsSubjects perceived small locomotor disturbances during both normal walking (dominant: 0.07 ± 0.03 m/s, non-dominant: 0.08 ± 0.03 m/s) and while performing the secondary cognitive task (dominant: 0.08 ± 0.01 m/s, non-dominant: 0.09 ± 0.02 m/s). There was no significant difference between legs (p = 0.466), with the addition of the cognitive task (p = 0.08), or interaction between leg and task (p = 0.994). SignificanceThe ability to perceive subtle slip-like locomotor disturbances was maintained even when performing a cognitively distracting task, suggesting that young adults can perceive very small locomotor disturbances.

Preoperative and Postoperative Walking Gait in Women With Acetabular Labral Tears and Femoroacetabular Impingement Syndrome.

Symptomatic femoroacetabular impingement syndrome (FAIS) is a painful condition that leads to decreased function. How walking gait changes over time within the first year after surgery for FAIS and how these changes present in women are currently unknown. To determine biomechanical gait differences between women with FAIS or labral tears and control individuals preoperatively and at 3 and 6 months postoperatively. Case-control study. Laboratory. A total of 18 female participants comprising 9 women in the FAIS group (age = 31.44 ± 7.47 years, height = 1.73 ± 0.08 m, mass = 73.61 ± 14.44 kg) and 9 women in the control group (age = 31.44 ± 6.65 years, height = 1.69 ± 0.06 m, mass = 60.93 ± 5.58 kg). Between-groups comparisons of the Hip Outcome Score Activities of Daily Living subscale (HOSADL) and gait biomechanics were conducted preoperatively and at the 3- and 6-month postoperative sessions. Statistical parametric mapping was performed on normalized time-series data. Preoperatively, the FAIS group had poor HOSADL scores (FAIS group = 64.1 ± 15.4 versus control group = 100.0 ± 0, P < .001), walked 15% slower, and exhibited several gait differences compared with the control group. Three months postoperatively, the FAIS group displayed greater vertical ground reaction force (P = .01), ankle-dorsiflexion angle (P = .02), and external dorsiflexion moment (P = .01) in midstance, as well as a greater knee-flexion angle through the second half of stance (P < .001). The FAIS group also demonstrated less hip-extension angle (P = .02) and hip-abduction angle (P = .01) through the second half of stance, which transitioned into less hip extension (P = .040) and hip abduction (P = .03) during the subsequent swing phase. The FAIS group improved their HOSADL to 87.6 ± 7.6 by 6 months postoperatively and had a greater dorsiflexion moment (P = .003) and ankle external rotation during stance (P = .03). In addition, the FAIS group showed a greater external hip external-rotation moment in late stance (P < .001). The biomechanical differences between groups were most evident at 3 months postoperatively, suggesting that women with FAIS had more postoperative gait compensations in the short term after surgery. By 6 months postoperatively, patient-reported outcomes had markedly improved, and the FAIS group displayed few gait differences compared with the control group.

Evaluating the Effects of Underloaded and Overloaded Warm-ups on Subsequent Swing Velocity.

Miller, RM, Heishman, AD, Freitas, EDS, and Bemben, MG. Evaluating the effects of underloaded and overloaded warm-ups on subsequent swing velocity. J Strength Cond Res 34(4): 1071-1077, 2020-Several attempts to identify the optimal on-deck procedure to enhance swing velocity in baseball have been made. However, inconsistent findings continue to constitute much of the body of literature. In addition, the emergence of athlete monitoring in sport has led to the exploration of more sport-specific tasks to potentially identify athlete fatigue and readiness to perform. Therefore, the purpose of this investigation was to examine 3 different bat weight warm-up protocols on subsequent swing velocity and to examine the reliability of swing velocity measurements to allude to its potential a sport-specific athlete monitoring metric. Thirty-two recreational male baseball players 20.3 ± 2.0 years, 179.6 ± 7.1 cm and 89.6 ± 11.1 kg completed the study. Subjects completed 3 testing visits that included warming up with a control bat ([CB] 32 in., 29 oz), plastic bat ([PB] 31 in., 6.4 oz), or heavy bat ([HB] 32 in., 57 oz). Testing visits began with 3 CB swing trials followed by 3 intervention bat trials, then concluded with 3 additional CB swings. Swing velocity was assessed using visual 3D technology. Analyses of variance indicate that after the PB (26.6 ± 2.0 m·s) and CB interventions (26.2 ± 1.7 m·s) significantly faster (p < 0.001) swing velocities were generated when compared with the traditional HB intervention (24.1 ± 2.2 m·s). When assessed for reliability, the average ICC was 0.681 and Cronbach's alpha was 0.95, indicating exceptional reliability. Congruent to previous research, these data bolster the notion that warming up with a HB can hinder swing velocity. However, in contrast to previous research these data suggest that using a PB can increase swing velocity significantly. Furthermore, visual 3D can be designated as an exceptionally reliable device to measure swing velocity.

Assessing the Relative Contributions of Active Ankle and Knee Assistance to the Walking Mechanics of Transfemoral Amputees Using a Powered Prosthesis.

Powered knee-ankle prostheses are capable of providing net-positive mechanical energy to amputees. Yet, there are limitless ways to deliver this energy throughout the gait cycle. It remains largely unknown how different combinations of active knee and ankle assistance affect the walking mechanics of transfemoral amputees. This study assessed the relative contributions of stance phase knee swing initiation, increasing ankle stiffness and powered plantarflexion as three unilateral transfemoral amputees walked overground at their self-selected walking speed. Five combinations of knee and ankle conditions were evaluated regarding the kinematics and kinetics of the amputated and intact legs using repeated measures analyses of variance. We found eliminating active knee swing initiation or powered plantarflexion was linked to increased compensations of the ipsilateral hip joint during the subsequent swing phase. The elimination of knee swing initiation or powered plantarflexion also led to reduced braking ground reaction forces of the amputated and intact legs, and influenced both sagittal and frontal plane loading of the intact knee joint. Gradually increasing prosthetic ankle stiffness influenced the shape of the prosthetic ankle plantarflexion moment, more closely mirroring the intact ankle moment. Increasing ankle stiffness also corresponded to increased prosthetic ankle power generation (despite a similar maximum stiffness value across conditions) and increased braking ground reaction forces of the amputated leg. These findings further our understanding of how to deliver assistance with powered knee-ankle prostheses and the compensations that occur when specific aspects of assistance are added/removed.

Modification of hemiplegic compensatory gait pattern by symmetry-based motion controller of HAL.

As one of several characteristics of hemiplegic patients after stroke, compensatory gait caused by affected limb is often seen. The purpose of this research is to apply a symmetry-based controller of a wearable type lower limb robot, Hybrid Assistive Limb (HAL) to hemiplegic patients with compensatory gait, and to investigate improvement of gait symmetry. The controller is designed respectively for swing phase and support phase according to characteristics of hemiplegic gait pattern. The controller during swing phase stores the motion of the unaffected limb and then provides motion support on the affected limb during the subsequent swing using the stored pattern to realize symmetric gait based on spontaneous limb swing. Moreover, the controller during support phase provides motion to extend hip and knee joints to support wearer's body. Clinical tests were conducted in order to assess the modification of gait symmetry. Our case study involved participation of one chronic stroke patient who performs abnormally-compensatory gait for both of the affected and unaffected limbs. As a result, the patient's gait symmetry was improved by providing motion support during the swing phase on the affected side and motion constraint during the support phase on the unaffected side. The study showed promising basis for the effectiveness of the controller for the future clinical study.

Development of an assist controller with robot suit HAL for hemiplegic patients using motion data on the unaffected side.

Among several characteristics seen in gait of hemiplegic patients after stroke, symmetry is known to be an indicator of the degree of impairment of walking ability. This paper proposes a control method for a wearable type lower limb motion assist robot to realize spontaneous symmetric gait for these individuals. This control method stores the motion of the unaffected limb during swing and then provides motion support on the affected limb during the subsequent swing using the stored pattern to realize symmetric gait based on spontaneous limb swing. This method is implemented on the robot suit HAL (Hybrid Assistive Limbs). Clinical tests were conducted in order to assess the feasibility of the control method. Our case study involved participation of one chronic stroke patient who was not able to flex his right knee. As a result, the walking support for hemiplegic leg provided by the HAL improved the subject's gait symmetry. The feasibility study showed promising basis for the future clinical study.

Comparison of muscle activity patterns of transfemoral amputees and control subjects during walking

BackgroundOnly few studies have looked at electromyography (EMG) during prosthetic gait. Differences in EMG between normal and prosthetic gait for stance and swing phase were never separately analyzed. These differences can give valuable information if and how muscle activity changes in prosthetic gait.MethodsIn this study EMG activity during gait of the upper leg muscles of six transfemoral amputees, measured inside their own socket, was compared to that of five controls. On and off timings for stance and swing phase were determined together with the level of co-activity and inter-subject variability.Results and conclusionsGait phase changes in amputees mainly consisted of an increased double support phase preceding the prosthetic stance phase. For the subsequent (pre) swing phase the main differences were found in muscle activity patterns of the prosthetic limb, more muscles were active during this phase and/or with prolonged duration. The overall inter-subject variability was larger in amputees compared to controls.

Electrostatic Droplet Ejection Using Planar Needle Inkjet Head

For the purpose of investigating the electrostatic droplet ejection event, a planar needle inkjet head with a projected cone-shaped needle (3-D head) was prepared to observe the phenomenon of droplet ejection. As the initial approach to developing a liquid ejection monitoring method, electric current was also measured. The ejection was found to take place as a series of single events that are composed of fine droplet ejections forming the Taylor cone and the subsequent swing back of the liquid front owing to the relationship between surface tension and electrostatic force. The critical factors for ejecting fine droplets in the case of using the inkjet head having a protruding needle were back pressure from the reservoir and the wetting control of the structures. The fast Fourier transform of electric current revealed the appearance of periodic signals during ejection, which may be used in developing a technique of sensing droplet ejection.

A study on a brachiation controller for a multi-locomotion robot — realization of smooth, continuous brachiation

In this paper, we present a control method to realize smooth continuous brachiation. The target brachiation is basically divided into two actions: a swing action and a locomotion action. In order to realize the continuous brachiation effectively and smoothly, it is necessary to start the swing action as soon as the robot grasps the front target bar at the end of the locomotion action. The collision, which occurs at the moment the robot grips the target bar, affects the pendulum motion of the robot. The action of bending the elbow joint of the swinging arm is proposed in order to solve this gripping problem. The elbow-bending action enables the robot to decrease the impact forces and use the excess mechanical energy after the end of the locomotion phase. Thus, there is no loss of energy and waste of time during the subsequent swing phase. Experimental results show that the robot can successfully achieve smooth, continuous brachiation.

Understanding brachiation: insight from a collisional perspective.

Gibbons are able to brachiate effectively through the forest canopy with a suspended swinging motion via contact with handholds. The swing phase is unlikely to be a cause of significant energy loss as pendulums are able to oscillate with only gradual mechanical energy dissipation. We consider the energetics associated with the transition of either a swing (during continuous-contact brachiation) or a ballistic flight (ricochetal brachiation) to a subsequent swing. In both styles of brachiation, kinematic data suggest that a gibbon overshoots the path that would allow a smooth transition into the swing phase. The sudden change in velocity due to such an overshoot is associated with a collision. Assuming neither the handhold nor the gibbon stores elastic strain energy, the energetic consequences of such overshoots can be calculated. We suggest two reasons for overshooting smooth transition trajectories: in the case of continuous contact brachiation, excess mechanical energy can be maintained with a high amplitude swing, and an overshoot during ricochetal brachiation produces a safety margin. The degree of energy loss with the transition to the swing phase is dependent both on the alignment of the pre- and post-transition paths, and on the kinetic energy at that instant. Active mechanisms reduce the effects of overshoots in both brachiation gaits. During continuous-contact brachiation, the path of the centre of mass can be controlled actively by flexion both of the trailing arm and the legs. During ricochetal brachiation, the length between the hand and the centre of mass (determining the subsequent swing path) can be controlled throughout the flight phase with leg flexion/extension. In addition, the elongated arms characteristic of gibbons improves the geometry of a collision for a given overshoot, and so may be viewed as a morphological adaptation reducing the energetic losses caused by overshooting for safety.

After-effects of using a weighted bat on subsequent swing velocity and batters' perceptions of swing velocity and heaviness.

In baseball and softball, warm-up swings with a weighted bat have been believed to increase swing velocity when an ordinary bat is used in the subsequent competitive situation. The purpose of this study was to investigate the after-effects of using a weighted bat on subsequent swing velocity and batters' perceptions of swing velocity and heaviness. Eight men in varsity softball and baseball hit a ball suspended from the ceiling 45 times (3 sets of 15 trials). For each set, the initial 5 trials were done using an ordinary 920-g wooden bat (Control condition), and the following 5 trials by a bat with an 800-g bat ring (Weighted condition), and the final 5 trials again by the ordinary bat (post-Weighted condition). Analysis of variance showed a significant decrease of 3.3% in the measured linear velocity of the bat prior to impact with the ball for the first swing of the post-Weighted condition compared with the Control condition. From the second swing the velocity returned to the level of the Control condition. Subjective judgment of the heaviness and velocity of swings for the Weighted and post-Weighted conditions by each participant showed that the ordinary bat felt lighter and swing speed felt faster for the post-Weighted condition. The advantage of the warm-up with a weighted bat was thus psychological and not biomechanical.

AFTER-EFFECTS OF USING A WEIGHTED BAT ON SUBSEQUENT SWING VELOCITY AND BATTERS' PERCEPTIONS OF SWING VELOCITY AND HEAVINESS

In baseball and Softball, warm-up swings with a weighted bat have been believed to increase swing velocity when an ordinary bat is used in the subsequent competitive situation. The purpose of this study was to investigate the aftereffects of using a weighted bat on subsequent swing velocity and batters' perceptions of swing velocity and heaviness. Eight men in varsity Softball and baseball hit a ball suspended from the ceiling 45 times (3 sets of 15 trials). For each set, the initial 5 trials were done using an ordinary 920-g wooden bat (Control condition), and the following 5 trials by a bat with an 800-g bat ring (Weighted condition), and the final 5 trials again by the ordinary bat (post-Weighted condition). Analysis of variance showed a significant decrease of 3.3% in the measured linear velocity of the bat prior to impact with the ball for the first swing of the post-Weighted condition compared with the Control condition. From the second swing the velocity returned to the level of the Control condition. Subjective judgment of the heaviness and velocity of swings for the Weighted and post-Weighted conditions by each participant showed that the ordinary bat felt lighter and swing speed felt faster for the post-Weighted condition. The advantage of the warm-up with a weighted bat was thus psychological and not biomechanical.

Muscular responses and movement strategies during stumbling over obstacles.

Although many studies have investigated reflexes after stimulation of either cutaneous or proprioceptive afferents, much less is known about responses after more natural perturbations, such as stumbling over an obstacle. In particular, the phase dependency of these responses and their relation to the stumbling behavior has received little attention. Hence response strategies during stumbling reactions after perturbations at different times in the swing phase of gait were studied. While subjects walked on a treadmill, a rigid obstacle unexpectedly obstructed the forward sway of the foot. All subjects showed an "elevating strategy" after early swing perturbations and a "lowering strategy" after late swing perturbations. During the elevating strategy, the foot was directly lifted over the obstacle through extra knee flexion assisted by ipsilateral biceps femoris (iBF) responses and ankle dorsiflexion assisted by tibialis anterior (iTA) responses. Later, large rectus femoris (iRF) activations induced knee extension to place the foot on the treadmill. During the lowering strategy, the foot was quickly placed on the treadmill and was lifted over the obstacle in the subsequent swing. Foot placement was actively controlled by iRF and iBF responses related to knee extension and deceleration of the forward sway. Activations of iTA mostly preceded the main ipsilateral soleus (iSO) responses. For both strategies, four response peaks could be distinguished with latencies of approximately 40 ms (RP1), approximately 75 ms (RP2), approximately 110 ms (RP3), and approximately 160 ms (RP4). The amplitudes of these response peaks depended on the phase in the step cycle. The phase-dependent modulation of the responses could not be accounted for by differences in stimulation or in background activity and therefore is assumed to be premotoneuronal in origin. In mid swing, both the elevating and lowering strategy could occur. For this phase, the responses of the two strategies could be compared in the absence of phase-dependent response modulation. Both strategies had the same initial electromyographic responses till approximately 100 ms (RP1-RP2) after perturbation. The earliest response (RP1) is assumed to be a short-latency stretch reflex evoked by the considerable impact of the collision, whereas the second (RP2) has features reminiscent of cutaneous and proprioceptive responses. Both these responses did not determine the behavioral response strategy. The functionally important response strategies depended on later responses (RP3-RP4). These data suggest that during stumbling reactions, as a first line of defense, the CNS releases a relatively aspecific response, which is followed by an appropriate behavioral response to avoid the obstacle.

New fast valving scheme using parallel valves for transient stability improvement

A new fast valving scheme of steam turbines using two parallel valves for improving the transient stability of a power system is proposed. The influence of the actuation time parameters of a conventional fast valving scheme using a single valve is first studied in detail to justify the need for a parallel valve scheme. A systematic procedure for selecting suitable valve actuation times, the sequence and the conditions to be monitored for implementing a coordinated parallel valve actuation scheme is presented. The proposed scheme is applied to a typical nuclear power plant connected to an infinite busbar system. A four stroke valve operation mode of the scheme is found to improve the second and subsequent swing stability significantly. A multiple stroke operation mode of the scheme for improving the rotor angle damping over a longer period of transient is also presented.

Adaptive control for backward quadrupedal walking. III. Stumbling corrective reactions and cutaneous reflex sensitivity

1. Four cats were trained to walk backward (BWD) and forward (FWD) on a motorized treadmill. Mechanical (taps) or electrical (pulses) stimuli were applied to the dorsal or ventral aspect of the hind paw during swing or stance. Hindlimb kinematic data, obtained by digitizing 16-mm high-speed film, were synchronized with computer-analyzed electromyograms (EMG) recorded from anterior biceps femoris (ABF), vastus lateralis (VL), lateral gastrocnemius (LG), tibialis anterior (TA), and semitendinosus (ST). Responses to taps and pulses, as well as the modulation in cutaneous reflex sensitivity to pulses, were described for both walking directions and stimulus locations. 2. After dorsal taps that obstructed FWD swing, the hindlimb initially drew back away from the obstacle with knee flexion and ST activation, ankle extension with TA suppression and LG activation, and hip extension with ABF facilitation. Next, the limb was raised over the obstacle with resumed TA activity and enhanced knee and ankle flexion, and then compensatory knee and ankle extension positioned the limb for the ensuing stance phase. 3. For ventral taps that obstructed BWD swing, the initial response also tended to draw the limb away from the obstacle with hip and ankle flexion and TA facilitation and reduced knee flexion with weak VL facilitation and suppression of ST activity. Next, ST activity resumed as knee and ankle flexion raised the limb over the obstacle, and then compensatory extension completed the swing phase for BWD walking. Thus the initial kinematic and EMG responses to obstacles were opposite for BWD versus FWD swing, and these responses were consistent with active avoidance of the obstacles. Responses during BWD walking were subtle, however, compared with those for FWD. 4. After nonobstructing taps (ventral FWD, dorsal BWD), ST and TA activation and knee and ankle flexion were coincident, demonstrating that the aforementioned differences in responses to obstructing obstacles were not simply location dependent. Regardless of the direction of walking or the location of stimulation, taps applied during stance had little immediate kinematic effect, but the subsequent swing phase was usually exaggerated, as if the response was programmed to avoid any lingering obstacle. 5. Electrical pulses did not elicit the full-blown responses typically evoked by taps. The sequencing in activation of ST and TA characteristic after laps was absent after pulses, and there were rarely dramatic kinematic responses to pulses like those easily elicited by taps. There were, in fact, few differences in responses to electrical stimulation for BWD versus FWD walking.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterizing bone strain distributions in vivo using three triple rosette strain gages

Three triple-element rosette strain gages were attached to the equine third metacarpal midshaft to record site-specific strains engendered by locomotion. The distribution of strains acting upon the midshaft cross section were characterized using a combined beam theory and finite element model analysis that did not presume the manner by which the bone was inertially loaded. A medium-speed trot (3.6 m s−1) was chosen as a representative speed and gait, with normal and shear strains, and strain energy density (SED) distributions determined throughout the stance and subsequent swing phase. Importantly, the sites of maximum compression (−2400 μϵ), tension (810 μϵ), shear (1500 μϵ), and SED (54 kPa) were not located at any of the gage attachment sites, emphasizing that a minimum of three rosette gages are necessary to resolve the peaks and locations of functionally induced normal and shear strains. Considering the nonuniform strain distributions across the cortex, we conclude that the third metacarpal is subject to a complex loading milieu comprised of bending, axial compression, end shear, and torsion. As this complex manner of loading was consistent through the entire stance phase, it would appear that, at least during the trot, specific sites within the same cross section are subject to vastly different magnitudes of strain stimulus.