Whole-body Response for Pedestrian Impact with a Generic Sedan Buck.

To serve as tools for assessing injury risk, the biofidelity of whole-body pedestrian impact dummies should be validated against reference data from full-scale pedestrian impact tests. To facilitate such evaluations, a simplified generic vehicle-buck has been recently developed that is designed to have characteristics representative of a generic small sedan. Three 40 km/h pedestrian-impact tests have been performed, wherein Post Mortem Human Surrogates (PMHS) were struck laterally in a mid-gait stance by the buck. Corridors for select trajectory measures derived from these tests have been published previously. The goal of this study is to act as a companion dataset to that study, describing the head velocities, body region accelerations (head, spine, pelvis, lower extremities), angular velocities, and buck interaction forces, and injuries observed during those tests. Scaled, transformed head accelerations exceeded 80 g prior to head contact with the windshield for two of the three tests. Head xaxis angular velocity exceeded 40 rad/s prior to head contact for all three tests. In all cases the peak resultant head velocity relative to the vehicle was greater than the initial impact speed of the vehicle. Corridors of resultant head velocity relative to the vehicle were also developed, bounded by the velocities observed in these tests combined with those predicted to occur if the PMHS necks were perfectly rigid. These results, along with the other kinematic and kinetic data presented, provide a resource for future pedestrian dummy development and evaluation.

Etiology and Biomechanics of Tarsometatarsal Injuries in Professional Football Players: A Video Analysis.

BACKGROUND: Tarsometatarsal (TMT) dislocations are uncommon yet debilitating athletic injuries, particularly in American football. To date, the mechanisms of athletic TMT dislocation have been described only anecdotally. This lack of information confounds the development of preventative countermeasures. PURPOSE: To use video analysis to provide direct, independent identification of the etiologic and mechanistic variables responsible for TMT dislocations in professional football players. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Sixteen professional National Football League players who sustained publicly reported TMT dislocations were identified. Publicly broadcast game footage of the plays in which injury occurred was reviewed by a panel of 5 biomechanists. Consensus was reached regarding the details surrounding injury, and a weighting was assigned to each detail based on the panel's confidence. RESULTS: Roughly 90% of injuries occurred while the injured player was engaged with or by another player, a detail that has heretofore been undocumented. Few injuries resulted from direct loading of either the foot or the ipsilateral limb; however, the injured foot was frequently subjected to axial loading from ground engagement with the foot in plantar flexion and the toes dorsiflexed. Injurious loading was often due to external rotation of the midfoot (86%). Fifteen of 16 injuries were season ending. CONCLUSION: TMT dislocations are frequently associated with engagement by or with a second player but infrequently caused by a direct blow to the foot. Axial loading of the foot, external rotation, and pronation/supination are the most common conditions during injurious loading.

Development of an injury risk function for first metatarsophalangeal joint sprains.

INTRODUCTION: Sprains of the first metatarsophalangeal (1MTP) joint, also known as turf toe, are debilitating athletic injuries. Because 85% of 1MTP sprains result from excessive hallux dorsiflexion, interventions that limit motion to subinjurious levels would greatly benefit athletes. Hallux dorsiflexion range of motion (hdROM) cannot be overly constrained, however, lest athletic performance be compromised. Therefore, the tolerance of the 1MTP joint to excessive dorsiflexion injury must be quantified before appropriate hdROM limitations may be developed. The purpose of this study was to develop a quantitative injury risk function for 1MTP sprains on the basis of hallux dorsiflexion angle. METHODS: Twenty cadaveric limbs were tested to both subinjurious and injurious levels of hallux dorsiflexion. Motion capture techniques were used to track six-degree-of-freedom motion of the first proximal phalanx, first metatarsal, and calcaneus. Specimens were examined by physicians posttest to diagnose injury occurrence and ensure clinical relevance of the injuries. RESULTS: A two-parameter Weibull hazard function analysis reveals that a 50% risk of injury occurs at 78° of dorsiflexion from anatomical zero. CONCLUSION: Methods presented here drove cadaveric 1MTP joints to various degrees of dorsiflexion, resulting in both noninjurious and injurious trials, which were formed into an injury risk function.

Foot kinematics and loading of professional athletes in American football-specific tasks.

The purpose of this study was to describe stance foot and ankle kinematics and the associated ground reaction forces at the upper end of human performance in professional football players during commonly performed football-specific tasks. Nine participants were recruited from the spring training squad of a professional football team. In a motion analysis laboratory setting, participants performed three activities used at the NFL Scouting Combine to assess player speed and agility: the 3-cone drill, the shuttle run, and the standing high jump. The talocrural and first metatarsophalangial joint dorsiflexion, subtalar joint inversion, and the ground reaction forces were determined for the load bearing portions of each activity. We documented load-bearing foot and ankle kinematics of elite football players performing competition-simulating activities, and confirmed our hypothesis that the talocrural, subtalar, and metatarsophalangeal joint ranges of motion for the activities studied approached or exceeded reported physiological limits.

A three-dimensional kinematic and kinetic comparison of overground and treadmill walking in healthy elderly subjects.

BACKGROUND: Instrumented treadmills offer a number of advantages for the biomechanical analysis of elderly gait, yet it is unclear how closely treadmill gait approximates overground gait. Although studies have indicated that the kinematics and kinetics of overground and treadmill gait are very similar in young adults, it still needs to be determined whether data collected in elderly adults during treadmill walking can be generalized to overground gait. The purpose of this study, therefore, was to compare the three-dimensional kinematics and kinetics of treadmill gait to overground gait in a group of healthy elderly subjects. METHODS: Three-dimensional kinematic and kinetic data for 18 healthy, nondisabled elderly subjects, age 65-81 years, were collected for speed-matched overground and treadmill walking conditions. FINDINGS: Overall, the kinematics and kinetics of gait during treadmill and overground walking in the elderly had very similar patterns. However, during treadmill walking elderly subjects showed greater cadence, smaller stride length and stride time as well as reductions in the majority of joint angles, moments and powers when compared to overground walking. INTERPRETATION: The large increase in cadence suggests that an effective method of acclimation to treadmill walking still needs to be determined. Because of the differences, we believe that in order for instrumented treadmills to become a suitable tool for research and training purposes in healthy elderly, subjects must be adequately acclimated to the treadmill.

Lower limb joint kinetics during moderately sloped running.

CONTEXT: Knowledge of the kinetic changes that occur during sloped running is important in understanding the adaptive gait-control mechanisms at work and can provide additional information about the poorly understood relationship between injury and changes in kinetic forces in the lower extremity. A study of these potential kinetic changes merits consideration, because training and return-to-activity programs are potentially modifiable factors for tissue stress and injury risk. OBJECTIVE: To contribute further to the understanding of hill running by quantifying the 3-dimensional alterations in joint kinetics during moderately sloped decline, level, and incline running in a group of healthy runners. DESIGN: Crossover study. SETTING: Three-dimensional motion analysis laboratory. PATIENTS OR OTHER PARTICIPANTS: Nineteen healthy young runners/joggers (age = 25.3 +/- 2.5 years). INTERVENTION(S): Participants ran at 3.13 m/s on a treadmill under the following 3 different running-surface slope conditions: 4 degrees decline, level, and 4 degrees incline. MAIN OUTCOME MEASURE(S): Lower extremity joint moments and powers and the 3 components of the ground reaction force. RESULTS: Moderate changes in running-surface slope had a minimal effect on ankle, knee, and hip joint kinetics when velocity was held constant. Only changes in knee power absorption (increased with decline-slope running) and hip power (increased generation on incline-slope running and increased absorption on decline-slope running in early stance) were noted. We observed an increase only in the impact peak of the vertical ground reaction force component during decline-slope running, whereas the nonvertical components displayed no differences. CONCLUSIONS: Running style modifications associated with running on moderate slopes did not manifest as changes in 3-dimensional joint moments or in the active peaks of the ground reaction force. Our data indicate that running on level and moderately inclined slopes appears to be a safe component of training regimens and return-to-run protocols after injury.

Changes in hip joint muscle-tendon lengths with mode of locomotion.

We have reported that peak hip extension is nearly identical in walking and running, suggesting that anatomical constraints, such as flexor muscle tightness may limit the range of hip extension. To obtain a more mechanistic insight into mobility at the hip and pelvis we examined the lengths of the muscle-tendons units crossing the hip joint. Data defining the three-dimensional kinematics of 26 healthy runners at self-selected walking and running speeds were obtained. These data were used to scale and drive musculoskeletal models using OpenSIM. Muscle-tendon unit (MTU) lengths were calculated for the trailing limb illiacus, rectus femoris, gluteus maximus, and biceps femoris long head and the advancing limb biceps femoris and gluteus maximus. The magnitude and timing of MTU length peaks were each compared between walking and running. The peak length of the right (trailing limb) illiacus MTU, a pure hip flexor, was nearly identical between walking and running, while the maximum length of the rectus femoris MTU, a hip flexor and knee extensor, increased during running. The maximum length of the left (leading limb) biceps femoris was also unchanged between walking and running. Further, the timing of peak illiacus MTU length and peak contralateral biceps femoris MTU length occurred essentially simultaneously during running, at a time during gait when the hamstrings are most vulnerable to stretch injury. This latter finding suggests exploring the role for hip flexor stretching in combination with hamstring stretching to treat and/or prevent running related hamstring injury.

Differences in static and dynamic measures in evaluation of talonavicular mobility in gait.

STUDY DESIGN: Controlled laboratory study using a cross-sectional design. OBJECTIVES: To compare the measurements of navicular drop during walking and running to those made clinically during a static position in a group of healthy young adults. BACKGROUND: The navicular drop test is a common clinical measure of foot structure and, more specifically, of talonavicular joint function. Previous work has focused on static measurement to establish the relationship between navicular drop and various overuse injuries. However, loads on foot structure are dramatically increased during gait. Examining navicular drop dynamically is more reflective of the functional demands of the foot when walking and running. METHODS: The navicular drop of 72 healthy runners was evaluated using 2 static methods. Results were used to classify individuals into groups and compared to dynamic measures of navicular drop made during walking and running. Three-dimensional motion capture and an instrumented treadmill were used to assess dynamic navicular mobility. A repeated-measures analysis of variance (ANOVA) was performed to examine differences between measurement conditions. Between-group differences were assessed with independent-samples t test (P<.05). RESULTS: Static measures of navicular drop were not found to be uniformly predictive of dynamic function during walking or running. Functional navicular drop measurements underestimated the dynamic measures in all foot types, while subtalar neutral drop overestimated dynamic measures for individuals with neutral and hypermobile foot types. No differences in navicular drop were found between foot types during walking, and small differences were found in running only between the hypomobile and hypermobile foot types. Maximum foot deformation during gait occurs at the time of maximum ground reaction force. Significant differences in navicular drop between foot type groups measured statically become muted when looking at group differences while walking and running. CONCLUSIONS: Differences in navicular mobility between foot type groups during walking and running indicate that factors other than static alignment affect dynamic foot mobility. Dynamic assessment of navicular mobility may be an effective tool to examine the interplay of how the extrinsic force demands of gait and intrinsic structure and neuromuscular control affect foot function in walking and running.

Changes in the coordination of hip and pelvis kinematics with mode of locomotion.

Limited hip extension mobility has been proposed as a possible cause of both increased anterior pelvic tilt and subsequent exaggerated lumbar lordosis during walking and running. The purpose of the present study was to examine the coordinated sagittal plane kinematic patterns of the hip and pelvis during walking and running in a substantial group of adult recreational runners. The kinematics of 73 healthy adult runners (age: 34+/-11years) were examined on an instrumented treadmill at self-selected walking and running speeds using a three-dimensional motion capture system. Although stride length increased considerably from walking to running, the range of hip extension utilized during running was not significantly greater than that during walking. Thigh extension and anterior pelvic tilt were significantly greater during running than walking. Also, a significant positive correlation was found between hip extension and anterior pelvic tilt during both walking and running, indicating that anterior pelvic tilt was greater in subjects that displayed reduced utilized peak hip extension. Thus, compensations for the increased stride length during running seem to occur at the pelvis, and presumably in the lumbar spine, rather than at the hip. Considering the association between anterior pelvic tilt and lumbar lordosis, the present findings may have clinical relevance regarding the prevention and treatment of hamstring injuries and of injuries to the lumbar spine.

Gait synchronized force modulation during the stance period of one limb achieved by an active partial body weight support system.

Our purpose was to demonstrate the ability of an actively controlled partial body weight support (PBWS) system to provide gait synchronized support during the stance period of a single lower extremity while examining the affect of such a support condition on gait asymmetry. Using an instrumented treadmill and a motion capture system, we compared gait parameters of twelve healthy elderly subjects (age 65-80 years) during unsupported walking to those while walking with 20% body weight support provided during only the stance period of the right limb. Specifically, we examined peak three-dimensional ground reaction force (GRF) data and the symmetry of lower extremity sagittal plane joint angles and of time and distance parameters. A reduction in all three GRF components was observed for the supported limb during modulated support. Reductions observed in the vertical GRF were comparable to the desired 20% support level. Additionally, GRF components examined for the unsupported limb during modulated support were consistently similar to those measured during unsupported walking. Modulated support caused statistically significant increases in asymmetry for knee flexion during stance (increased 5.9%), hip flexion during late swing (increased 9.1%), and the duration of single limb support (increased 2.8%). However, the observed increases were similar or considerably less than the natural variability in the asymmetry of these parameters during unsupported walking. The ability of the active PBWS device to provide unilateral support may offer new and possibly improved applications of PBWS rehabilitation for patients with unilateral walking deficits such as hemiparesis or orthopaedic injury.

A kinematics and kinetic comparison of overground and treadmill running.

PURPOSE: The purpose of this study was to compare the kinematic and kinetic parameters of treadmill running to those of overground running. METHODS: Twenty healthy young subjects ran overground at their self-selected moderate running speed. Motion capture and ground reaction force (GRF) data for three strides of each limb were recorded and the subjects' average running speed was evaluated. The subjects then ran on an instrumented treadmill set to their average overground running speed while motion capture and GRF data were recorded. The kinematics (body segment orientations and joint angles) and kinetics (net joint moments and joint powers) for treadmill (15 consecutive gait cycles) and overground running (three cycles each limb) were calculated and compared. RESULTS: The features of the kinematic and kinetic trajectories of treadmill gait were similar to those of overground gait. Statistically significant differences in knee kinematics,the peak values of GRF, joint moment, and joint power trajectories were identified. DISCUSSION: Parameters measured with an adequate instrumented treadmill are comparable to but not directly equivalent to those measured for overground running. With such an instrument, it is possible to study the mechanics of running under well-controlled and reproducible conditions. SIGNIFICANCE: Treadmill-based analysis of running mechanics can be generalized to overground running mechanics, provided the treadmill surface is sufficiently stiff and belt speed is adequately regulated.

The influence of arch supports on knee torques relevant to knee osteoarthritis.

PURPOSE: Changes in footwear and foot orthotic devices have been shown to significantly alter knee joint torques thought to be relevant to the progression if not the development of knee osteoarthritis (OA) in the medial tibiofemoral compartment. The purpose of this study was to determine if commonly prescribed arch support cushions promote a medial force bias during gait similar to medial-wedged orthotics, thereby increasing knee varus torque during both walking and running. METHODS: Twenty-two healthy, physically active young adults (age, 29.2 +/- 5.1 yr) were analyzed at their self-selected walking and running speeds in control shoes with and without arch support cushions. Three-dimensional motion capture data were collected in synchrony with ground reaction force (GRF) data collected from an instrumented treadmill. Peak external knee varus torque during walking and running were calculated through a full inverse dynamic model and compared. RESULTS: Peak knee varus torque was statistically significantly increased by 6% (0.01 +/- 0.02 N.m.(kg.m)(-1)) in late stance during walking and by 4% (0.03 +/- 0.03 N.m.(kg.m)(-1)) during running with the addition of arch support cushions. CONCLUSIONS: The addition of material under the medial aspect of the foot by way of a flexible arch support promotes a medial force bias during walking and running, significantly increasing knee varus torque. These findings suggest that discretion be employed with regard to the prescription of commonly available orthotic insoles like arch support cushions.

Physiological modulation of gait variables by an active partial body weight support system.

Partial body weight support (PBWS) systems used for rehabilitation status post-neurological and musculoskeletal pathologies and injuries are traditionally passive. Our purpose was to demonstrate the ability of an actively controlled PBWS system to provide a clinically relevant modulated support condition while investigating the impact of such a condition on the dynamics of gait. Using an instrumented treadmill and a motion capture system, we compared gait parameters of six healthy young adults (age 24-31 years) during unsupported walking to those under the assistance of two support conditions (a constant 20% body weight support, and a modulated support providing 20% body weight support during the loading response of each leg while allowing for an unsupported terminal stance). The modulated condition achieved support synchronized to gait cycle events with mean and maximum loading errors at the 20% body weight support level equal to 1.01 and 2.44 kg, respectively. Constant support significantly reduced sagittal plane hip angle range of motion and increased ankle platarflexion as compared to unsupported walking (p < 0.05). Also, a clear trend of decreased stride length was observed for constant support. No significant differences in these parameters were evident between the modulated support condition and unsupported walking. Ankle power generation and absorption both significantly decreased under constant support. The modulated support condition significantly increased ankle power absorption though showed no change in ankle power generation. The ability of the presented active PBWS device to provide individualized support schemes may offer new and possibly improved applications of PBWS rehabilitation.

A kinematic and kinetic comparison of overground and treadmill walking in healthy subjects.

INTRODUCTION: Gait evaluation protocols using instrumented treadmills will be increasingly used in the near future. For this reason, it must be shown that using instrumented treadmills will produce measures of the ground reaction force adequate for inverse dynamic analysis, and differences between treadmill and overground gait must be well characterized. METHODS: Overground walking kinetics were estimated with the subjects walking at their self-selected comfortable walking speed. For the treadmill gait trials, the subjects walked on two treadmills, such that heel-strike occurred on the forward treadmill and toe-off occurred on the trailing treadmill. The treadmill was set to the average overground walking speed. Overground and treadmill data were evaluated using Vicon Plug-in Gait. The differences between the maxima and minima of kinematic and kinetic parameters for overground and treadmill gait were evaluated. RESULTS: The kinematics of treadmill and overground gait were very similar. Twelve of 22 kinematic parameter maxima were statistically significantly different (p<0.05), but the magnitude of the difference was generally less than 2 degrees . All GRF maxima were found to be statistically significantly smaller for treadmill versus overground gait (p<0.05) as were 15 of 18 moment, and 3 of 6 power maxima. However, the magnitude of the differences was comparable to the variability in normal gait parameters. The sagittal plane ankle moments were not statistically different for treadmill and overground gait. DISCUSSION: We have shown that treadmill gait is qualitatively and quantitatively similar to overground gait. Differences in kinematic and kinetic parameters can be detected in matched comparisons, particularly in the case of kinetic parameters. However, the magnitudes of these differences are all within the range of repeatability of measured kinematic parameters. Thus, the mechanics of treadmill and overground gait are very similar. CLINICAL SIGNIFICANCE: Having demonstrated the essential equivalence of treadmill and overground gait, it is now possible for clinical movement analysis to take advantage of treadmill-based protocols.

Testing of a tri-instrumented-treadmill unit for kinetic analysis of locomotion tasks in static and dynamic loading conditions.

In this study, we present a multi-treadmill system instrumented with three force platforms capable of measuring vertical and shear ground reaction forces and moments during both walking and running. Linearity, belts speed variations, repeatability of the measures, cross-talk, natural frequency, instrumental noise, moving part induced noise and drift were investigated. The noise due to vibrations and to moving parts was also investigated having a subject walking and running on the treadmill. The linearity test results showed a high linearity of all three treadmill force platforms, and vertical force natural frequency values of 219, 308, 307Hz, obtained for the three force platforms, were considered appropriate for the investigation of walking and running. The instrumental noise did not appear to be a significant source of error. The characteristics of the noise due to vibrations and moving parts changed when in the presence of a subject walking and running on the treadmill. For walking trials, averaging of gait cycles led to a systematic improvement of the signal to noise ratio, particularly for the medio-lateral component of the force. For running trials, even though averaging was not as beneficial as for walking trials, the greater force amplitude led to a better signal to noise ratio value. This instrumented treadmill demonstrated acceptable accuracy and signal to noise ratios for all ground reaction force components such that it can be useful for a variety of research and clinical gait analysis applications.

Reduced hip extension in the elderly: dynamic or postural?

OBJECTIVE: To test the hypothesis that reduced hip extension and increased anterior pelvic tilt in the elderly are dynamic gait phenomena that do not occur during normal standing posture. DESIGN: Experimental. SETTING: Gait laboratory. PARTICIPANTS: Twenty-five older adult subjects (mean age +/- standard deviation, 71+/-5 y) and 25 young adult subjects (mean age, 26+/-5 y). INTERVENTION: Subjects were observed during standing and walking at self-determined comfortable, slow, and fast walking speeds. Positions and kinematics of the pelvis and lower extremities were measured using a 3-dimensional video-based motion analysis system. MAIN OUTCOME MEASURES: Peak hip extension and anterior pelvic tilt. RESULTS: There were no statistically significant differences between the older and young adult groups during standing with respect to either hip extension (3 degrees +/-5 degrees vs 1 degrees +/-6 degrees) or anterior pelvic tilt (11 degrees +/-5 degrees vs 10 degrees +/-5 degrees). On the other hand, at comfortable walking speeds, the older adult group had reduced peak hip extension (7 degrees +/-6 degrees vs 11 degrees +/-6 degrees , P<.05) and increased anterior pelvic tilt (15 degrees +/-5 degrees vs 11 degrees +/-5 degrees) compared with the young adult group. At fast walking speeds, peak hip extension was significantly reduced in the older adult group than in the young adult group (9 degrees +/-6 degrees vs 14 degrees +/-6 degrees , P<.05), but there was no significant difference at slow walking speeds (6 degrees +/-6 degrees vs 9 degrees +/-5 degrees ). CONCLUSIONS: Age-related changes in gait defined by reduced peak hip extension and increased pelvic tilt are dynamic rather than standing postural characteristics.

A clinical comparison of variable-damping and mechanically passive prosthetic knee devices.

OBJECTIVE: Although variable-damping knee prostheses offer some improvements over mechanically passive prostheses to transfemoral amputees, there is insufficient evidence that such prostheses provide advantages at self-selected walking speeds. In this investigation, we address this question by comparing two variable-damping knees, the hydraulic-based Otto Bock C-leg and the magnetorheological-based Ossur Rheo, with the mechanically passive, hydraulic-based Mauch SNS. DESIGN: For each prosthesis, metabolic data were collected on eight unilateral amputees walking at self-selected speeds across an indoor track. Furthermore, kinetic, kinematic, and electromyographic data were collected while walking at self-selected speeds across a 10-m walkway in a laboratory. RESULTS: When using the Rheo, metabolic rate decreases by 5% compared with the Mauch and by 3% compared with the C-leg. Furthermore, for the C-leg and Rheo knee devices, we observe biomechanical advantages over the mechanically passive Mauch. These advantages include an enhanced smoothness of gait, a decrease in hip work production, a lower peak hip flexion moment at terminal stance, and a reduction in peak hip power generation at toe-off. CONCLUSION: The results of this study indicate that variable-damping knee prostheses offer advantages over mechanically passive designs for unilateral transfemoral amputees walking at self-selected ambulatory speeds, and the results further suggest that a magnetorheological-based system may have advantages over hydraulic-based designs.

Moderate-heeled shoes and knee joint torques relevant to the development and progression of knee osteoarthritis.

OBJECTIVE: To determine if women's dress shoes with heels of just 1.5 in (3.8 cm) in height increases knee joint torques, which are thought to be relevant to the development and/or progression of knee osteoarthritis (OA) in both the medial and patellofemoral compartments. DESIGN: Randomized controlled trial. SETTING: A 3-dimensional motion analysis gait laboratory. PARTICIPANTS: Twenty-nine healthy young women (age, 26.7+/-5.0 y) and 20 healthy elderly adult women (age, 75.3+/-6.5 y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Peak external varus knee torque in early and late stance and prolongation of flexor knee torque in early stance. Three-dimensional data on lower-extremity torques and motion were collected during walking while (1) wearing shoes with 1.5-in high heels and (2) wearing control shoes without any additional heel. Data were plotted and qualitatively compared; major peak values and timing were statistically compared between the 2 conditions using paired t tests. RESULTS: Peak knee varus torque during late stance was statistically significantly greater with the heeled shoes than with the controls, with increases of 14% in the young women and 9% in the elderly women. With the heeled shoes, the early stance phase knee flexor torque was significantly prolonged, by 19% in the young women and by 14% in elderly women. Also, the peak flexor torque was 7% higher with the heeled shoe in the elderly women. CONCLUSIONS: Even shoes with moderately high heels (1.5 in) significantly increase knee torques thought to be relevant in the development and/or progression of knee OA. Women, particularly those who already have knee OA, should be advised against wearing these types of shoes.

Effects of treadmill walking speed on lateral gastrocnemius muscle firing.

OBJECTIVE: To study the electromyographic profile--including ON, OFF, and peak timing locations--of the lateral gastrocnemius muscle over a wide range of walking speeds (0.5-2.1 m/sec) in healthy young adults. DESIGN: We studied gastrocnemius muscle-firing patterns using an electromyographic surface electrode in 15 healthy subjects ambulating on a treadmill at their normal walking speed and at three paced walking speeds (0.5, 1.8, and 2.1 m/sec). Initial heel contact was determined from a force-sensitive switch secured to the skin over the calcaneous. RESULTS: For all speeds, the gastrocnemius firing pattern was characterized by a main peak, occurring 40-45% into the gait cycle, that increased in amplitude with walking speed. Speeds of > or =1.3 m/sec produced a common electromyographic timing profile, when the profile is expressed relative to the stride duration. However, at 0.5 m/sec (a speed typical of individuals with upper-motor neuron lesions), the onset of gastrocnemius firing was significantly delayed by 3-6% of the gait cycle and was prolonged by 8-11% of the gait cycle. CONCLUSION: Many patients with upper motor neuron lesions (e.g., stroke and traumatic brain injury) walk at speeds much slower than those commonly described in the literature for normal gait. At the slow walking speed of 0.5 m/sec, we have measured noticeable changes in the electromyographic timing profile of the gastrocnemius muscle. Given the importance of appropriate plantar flexor firing patterns to maximize walking efficiency, understanding the speed-related changes in gastrocnemius firing patterns may be essential to gait restoration.