Peak Ankle Moments Research Articles

Prediction of the optimal ankle foot orthosis stiffness using peak ankle moment when walking on shoes-only in neuromuscular diseases

Prediction of the optimal ankle foot orthosis stiffness using peak ankle moment when walking on shoes-only in neuromuscular diseases

Influence of Internal and External Foot Rotation on Peak Knee Adduction Moments and Ankle Moments during Gait in Individuals with Knee Osteoarthritis: A Cross-Sectional Study.

The aim of the study was to verify the effects of foot progression angle (FPA) modification during walking on the internal moments of the ankle and knee joints in individuals with knee osteoarthritis (OA). Biomechanical changes such as increased knee adduction moment (KAM) during walking are known to be involved in the development and severity of knee OA. Although various FPA modifications during gait have been applied to reduce peak KAM, few studies have investigated the effects of applying toe-in or toe-out walking modifications for knee OA on peak KAM and three-dimensional (3D) moments of the ankle joint. Kinetic moment variables were acquired from 35 individuals with medial knee compartment OA. A 3D motion analysis system and two force platforms were used to acquire KAM and 3D moments of both ankle joints during gait. Visual3D was used to obtain final moment data for statistical processing. Repeated-measures analysis of variance with Bonferroni adjustment was used to compare kinetic and kinematic values for each FPA walking condition. There was a significant decrease (p < 0.01) in first peak KAM when walking with an internal rotation foot position compared to normal foot position walking. Also, there was a significant decrease (p < 0.01) in second peak KAM when walking with an external rotation foot position compared to normal foot position walking. Compared to a normal foot position, peak ankle inversion moment of the external rotation foot position walking showed a significant decrease (p < 0.05). There were no interactive effects between FPA condition and limb sides for any KAM values (p > 0.05). The results showed no significant increase in the ankle joint moment value during gait for FPA modification conditions. Thus, the clinical implications of this study suggest that modification of the FPA in patients with OA to reduce KAM does not negatively impact the 3D ankle moments.

Effect of age on ankle biomechanics and tibial compression during stair descent

BackgroundStress fracture is a concern among older adults, as age-related decrements in ankle neuromuscular function may impair their ability to attenuate tibial compressive forces experienced during daily locomotor tasks, such as stair descent. Yet, it is unknown if older adults exhibit greater tibial compression than their younger counterparts when descending stairs. Research questionDo older adults exhibit differences in ankle biomechanics that alter their tibial compression during stair descent compared to young adults, and is there a relation between tibial compression and specific changes in ankle biomechanics? MethodsThirteen young (18–25 years) and 13 older (> 65 years) adults had ankle joint biomechanics and tibial compression quantified during a stair descent. Discrete ankle biomechanics (peak joint angle and moment, and joint stiffness) and tibial compression (maximum and impulse) measures were submitted to an independent t-test, while ankle joint angle and moment, and tibial compression waveforms were submitted to an independent statistical parametric mapping t-test to determine group differences. Pearson correlation coefficients (r) determined the relation between discrete ankle biomechanics and tibial compression measures for all participants, and each group. ResultsOlder adults exhibited smaller maximum tibial compression (p = 0.004) from decreases in peak ankle joint angle and moment between 17 % and 34 % (p = 0.035), and 20–31 % of stance (p < 0.001) than young adults. Ankle biomechanics exhibited a negligible to weak correlation with tibial compression for all participants, with peak ankle joint moment and maximum tibial compression (r = -0.48 ± 0.32) relation the strongest. Older adults typically exhibited a stronger relation between ankle biomechanics and tibial compression (e.g., r = -0.48 ± 0.47 vs r = -0.27 ± 0.52 between peak ankle joint moment and maximum tibial compression). SignificanceOlder adults altered ankle biomechanics and decreased maximum tibial compression to safely execute the stair descent. Yet, specific alterations in ankle biomechanics could not be identified as a predictor of changes in tibial compression.

Influence of altered torsional stiffness through sole modification of air pressure shoes on lower extremity biomechanical behaviour during side-step cutting maneuvers.

Directional changes in cutting maneuvers are critical in sports, where shoe torsional stiffness (STS) is an important factor. Shoes are designed based on different constructions and movement patterns. Hence, it is unclear how adjustable spacers into the sole constructions of air pressure chambers (APC) affect the STS in side-step cutting. Therefore, this study investigated the effects of altered STS through adjustable sole spacers on ground reaction force (GRF) and ankle and knee joint moments in side-step cutting. Seventeen healthy recreational athletes performed side-step cutting with experimental conditions including (i) barefoot (BF), (ii) unaltered shoes (UAS): soles consisting of APC, and (iii) altered shoes (AS): modified UAS by inserting elastomeric spacers into cavities formed by APC. Mechanical and biomechanical variables were measured. Significant differences were revealed across shoe conditions for impact peak (p = 0.009) and impulse (p = 0.018) in vertical GRF, time to achieve peak braking (p = 0.004), and peak propulsion (p = 0.025) for anterior-posterior GRF in ANOVA test. No significant differences were observed in GRF peaks and impulses between UAS and AS except for a trend of differences in impact peak (p = 0.087) for vertical GRF. At the ankle and knee joint, peak ankle power absorption (p = 0.019), peak knee internal rotation moment (p = 0.042), peak knee extension moment (p = 0.001), peak knee flexion moment (0.000), peak knee power absorption (p = 0.047) showed significant difference across three shoe conditions. However, no significant differences between the UAS and AS were noticed for peak joint moments and power. Altered shoe torsional stiffness did not significantly affect the peak forces and peak ankle and knee joint moments or powers; hence sole adjustment did not influence the cutting performance. This study might be insightful in sports footwear design, and adjusting shoe torsional stiffness by sole modification might be advantageous for athletes playing sports with cutting maneuvers to reduce the risk of injuries by controlling the twisting force at the ankle that frequently happens during cutting maneuvers.

Lower limb squat biomechanics and select clinical measures in chronic ankle instability

BackgroundIndividuals with chronic ankle instability often present with clinical and biomechanical abnormalities, however squat biomechanics have not been investigated. The purpose of this study was to compare select clinical assessments and squat biomechanics between individuals with and without chronic ankle instability. MethodsFifteen individuals with chronic ankle instability and a matched control group were studied. A weight-bearing dorsiflexion lunge test, foot posture, and an in-line half-kneeling motor control test for core stability were assessed. Lower limb 3D bilateral and unilateral squat biomechanics were captured. Groups, limbs and squat tasks were compared using an alpha of 0.05. FindingsIndividuals with chronic ankle instability had less static weight-bearing dorsiflexion and failed the core stability test more frequently, but did not differ in foot morphology compared to the controls. When squatting, those with chronic ankle instability demonstrated reduced peak ankle dorsiflexion angles and moments in the involved limb (p < 0.04) during single limb squats and had interlimb differences in ankle dorsiflexion angle as well as hip and knee kinetics (p < 0.04) during double limb squats. In those with chronic ankle instability, there was less overall motion, but higher kinetic demands in single limb versus double leg squatting (p < 0.03). InterpretationIndividuals with chronic ankle instability had impaired weight-bearing dorsiflexion and showed impaired core stability more often, which accompanied altered squatting mechanics in both variations. Within the limbs with chronic ankle instability, single limb squats showed lesser kinematic demands but higher kinetic demands than double limb squatting.

Effects of ankle exoskeleton assistance and plantar pressure biofeedback on incline walking mechanics and muscle activity in cerebral palsy

Ankle dysfunction affects more than 50 % of people with cerebral palsy, resulting in atypical gait patterns that impede lifelong mobility. Incline walking requires increased lower limb effort and is a promising intervention that targets lower-limb extensor muscles. A concern when prescribing incline walking to people with gait deficits is that this exercise may be too challenging or reinforce unfavorable gait patterns. This study aims to investigate how ankle exoskeleton assistance and plantar pressure biofeedback would affect gait mechanics and muscle activity during incline walking in CP. We recruited twelve children and young adults with CP. Participants walked with ankle assistance alone, biofeedback alone, and the combination while we assessed ankle, knee, and hip mechanics, and plantar flexor and knee extensor activity. Compared to incline walking without assistance or biofeedback, ankle assistance alone reduced the peak biological ankle moment by 12 % (p < 0.001) and peak soleus activity by 8 % (p = 0.013); biofeedback alone increased the biological ankle moment (4 %, p = 0.037) and power (19 %, p = 0.012), and plantar flexor activities by 9 – 27 % (p ≤ 0.026); assistance-plus-biofeedback increased biological ankle and knee power by 34 % and 17 %, respectively (p ≤ 0.05). The results indicate that both ankle exoskeleton assistance and plantar pressure biofeedback can effectively modify lower limb mechanics and muscular effort during incline walking in CP. These techniques may help in establishing personalized gait training interventions by providing the ability to adjust intensity and biomechanical focus over time.

Mechanics of The Medial Gastrocnemius-Tendon Unit in Behaving more Efficiently in Habitual Non-Rearfoot Strikers than in Rearfoot Strikers during Running.

This study aims to quantify how habitual foot strike patterns would affect ankle kinetics and the behavior and mechanics of the medial gastrocnemius-tendon unit (MTU) during running. A total of 14 runners with non-rearfoot strike patterns (NRFS) and 15 runners with rearfoot strike patterns (RFS) ran on an instrumented treadmill at a speed of 9 km/h. An ultrasound system and a motion capture system were synchronously triggered to collect the ultrasound images of the medial gastrocnemius (MG) and marker positions along with ground reaction forces (GRF) during running. Ankle kinetics (moment and power) and MG/MTU behavior and mechanical properties (MG shortening length, velocity, force, power, MTU shortening/lengthening length, velocity, and power) were calculated. Independent t-tests were performed to compare the two groups of runners. Pearson correlation was conducted to detect the relationship between foot strike angle and the MTU behavior and mechanics. Compared with RFS runners, NRFS runners had 1) lower foot strike angles and greater peak ankle moments; 2) lower shortening/change length and contraction velocity and greater MG peak force; 3) greater MTU lengthening, MTU shortening length and MTU lengthening velocity and power; 4) the foot strike angle was positively related to the change of fascicle length, fascicle contraction length, and MTU shortening length during the stance phase. The foot strike angle was negatively related to the MG force and MTU lengthening power. The MG in NRFS runners appears to contract with greater force in relatively isometric behavior and at a slower shortening velocity. Moreover, the lengthening length, the lengthening velocity of MTU, and the MG force were greater in habitual NRFS runners, leading to a stronger stretch reflex response potentially.

Females with hip-related pain demonstrate reduced kinetics at the hip and ankle during terminal stance of gait

BackgroundIndividuals with hip-related pain (HRP) commonly report pain with walking and demonstrate altered movement patterns compared to healthy controls (HCs). Individuals with HRP may attempt to reduce pain during walking by decreasing kinetics and joint forces at the hip through increased use of the ankle during pushoff. Research questionDo individuals with HRP have increased kinetics at the ankle and decreased kinetics at the hip during pushoff in gait compared to HCs, and do kinetic patterns differ between males and females with HRP? MethodsThis retrospective observational study included 42 individuals with HRP and 20 HCs. Participants completed overground gait trials at their self-selected speed while kinematics and kinetics were recorded through a motion capture system and force plates. Peak internal hip and ankle moments and hip flexion and ankle plantarflexion angular impulse during terminal stance were used in general estimating equations for comparison of group by limb interactions for males and females separately, as well as a comparison of males and females within the HRP group. ResultsFemales with HRP demonstrated reduced hip flexion impulse on their involved limb (.070 Nm*s/kg*m) compared to female HCs (.083Nm*s/kg*m; p = .032), as well as reduced peak ankle plantarflexion moment (−.94Nm/kg*m) compared to their contralateral limb (−.99Nm/kg*m) and the involved limb of HRP males (−1.00Nm/kg*m) (p ≤ .007). There were no between-limb or between-group differences in hip or ankle peak moments or impulses in males. SignificanceFemales with HRP show decreased kinetics at both the hip and ankle; these patterns were not identified in males. Future investigations should examine whether increasing ankle kinetics during pushoff reduces pain at the hip, as this may be a valuable clinical treatment strategy.

Timing of propulsion-related biomechanical variables is impaired in individuals with post-stroke hemiparesis

BackgroundIn individuals with post-stroke hemiparesis, reduced paretic leg propulsion, measured through anterior ground reaction forces (AGRF), is a common and functionally-relevant gait impairment. Deficits in other biomechanical variables such as plantarflexor moment, ankle power, and ankle excursion contribute to reduced propulsion. While reduction in the magnitude of propulsion post-stroke is well studied, here, our objective was to compare the timing of propulsion-related biomechanical variables. Research questionAre there differences in the timing of propulsion and propulsion-related biomechanical variables between able-bodied individuals, the paretic leg, and non-paretic leg of post-stroke individuals? MethodsNine able-bodied and 13 post-stroke individuals completed a gait analysis session comprising treadmill walking trials at each participant’s self-selected speed. Two planned independent sample t-tests were conducted to detect differences in the timing of dependent variables between the paretic versus non-paretic leg post-stroke and paretic leg versus the dominant leg of able-bodied individuals. ResultsPost-stroke individuals demonstrated significantly earlier timing of peak AGRF of their paretic leg versus their non-paretic leg and able-bodied individuals. Post-stroke participants displayed earlier timing of peak power of their paretic leg versus their non-paretic leg and able-bodied individuals, and earlier timing of peak ankle moment of the paretic leg versus able-bodied. No significant differences were detected in the timing of peak ankle angle. SignificanceThe earlier onset of peak AGRF, peak ankle power, and peak ankle moment may be an important, under-studied biomechanical factor underlying stroke gait impairments, and a potential therapeutic target for stroke gait retraining. Future investigations can explore the use of interventions such as gait biofeedback to normalize the timing of these peaks, thereby improving propulsion and walking function post-stroke.

The Effects of Tai Chi Chuan Exercise Training on the Lower Extremities of Middle-Aged and Elderly

Background: It is known that lower-limb muscle strength is easily maintained in elderly people who practice Tai Chi, although it is necessary to maintain lower-limb muscle strength even as age increases in order to prevent falls. However, the effect of long-term Tai Chi practice and age on lower-limb ability is unclear in middle-aged and elderly people. This research was designed to compare lower-extremity parameters during a countermovement jump between middle-aged and elderly individuals who frequently practice Tai Chi Chuan and individuals in the general population who constituted the healthy group. Methods: There were four groups, and each group included 12 participants. Ten Vicon motion system infrared cameras and two Kistler force plates were used. The data were standardized and analysed using independent-measure two-way ANOVA. Results: The statistical results showed that there was no interaction between the age factor and exercise type factor. The statistics of age factor also showed that age may decrease the jump height (36.36%), peak knee power (24.74%) and peak ankle power (21%) during the take-off phase. In the exercise type factor, long-term Tai Chi training significantly increased the jump height (60%), peak knee moment (19.80%), peak ankle moment (8.06%), peak hip power (29.80%), peak knee power (31.23%) and peak ankle power (16.88%) during the take-off phase. Conclusion: This study shows that long-term Tai Chi training can slow ageing-related functional decline. According to the results of this study, middle-aged and elderly people are encouraged to regularly perform Tai Chi exercises to increase the strength of various muscle groups in the lower limbs and slow the lower-limb muscle changes caused by ageing.

Surgical treatment of chronic Achilles tendon rupture results in improved gait biomechanics

BackgroundChronic Achilles tendon rupture is associated with persistent weakness at push-off with the affected foot and poor balance, resulting in significant alterations to normal gait. Surgical repair is the most common treatment for improving gait in patients with a Chronic Achilles tendon rupture, but, to date, the outcomes have not been quantified in the literature.MethodsA total of 23 patients with a Chronic Achilles tendon rupture (mean age 61 ± 15 years) underwent three-dimensional gait analysis according to a standardized protocol using an optical tracking system. Data of spatiotemporal, kinematic and kinetic variables were collected preoperatively and one year postoperatively. In addition, the postoperative gait biomechanics were compared with the gait biomechanics of a control group consisting of 70 healthy individuals (mean age 49 ± 20 years). The prospectively collected data were analyzed by an independent t test.ResultsPostoperatively, increments were found in gait speed (mean difference − 0.12 m/s), stride length (− 0.12 m), peak ankle moment (− 0.64 Nm/kg), peak ankle power (− 1.38 W/kg), peak knee power (− 0.36 m) and reduced step width (0.01 m), compared with preoperative gait biomechanics (p < 0.014). Compared with the control group, patients with a Chronic Achilles tendon rupture exhibited slower postoperative gait speed (mean difference 0.24 m/s), wider step width (− 0.02 m), shorter stride length (0.16 m), longer relative stance phase (− 2.15%), lower peak knee flexion (17.03 degrees), greater peak knee extension (2.58 degrees), lower peak ankle moment (0.35 Nm/kg), peak ankle power (1.22 W/kg) and peak knee power (1.62 W/kg), (p < 0.010).ConclusionSurgical intervention and postoperative rehabilitation can be an effective treatment for alterations in gait after a Chronic rupture of the Achilles tendon. However, at one year postoperatively, patients still exhibit impairments in spatiotemporal variables and knee and ankle power compared with healthy controls.

Sensitivity of a Subject-specific Ankle Sprain Simulation to Extrinsic Versus Intrinsic Biomechanical Factors.

Ankle sprains are the most common musculoskeletal injury in sport and military activity, despite existing prophylactic strategies. The purpose of this report was to develop a probabilistic simulation of lateral ankle sprains during single-limb drop landing, towards accelerating innovation in ankle sprain prevention. A deterministic, subject-specific musculoskeletal model was extended with automation and probabilistic distributions on sprain-related biomechanical factors. Probabilistic simulations were generated using traditional Monte Carlo techniques and the advanced mean value method, a more computationally-efficient approach. Predicted distributions of peak ankle joint rotations, velocities, and moments borne by supporting passive structures agreed favorably with the deterministic model and with reports of real sprain biomechanics. Parameter sensitivities identified that predictions were most strongly influenced by drop height, subtalar joint posture at contact, invertor/evertor co-activation, and passive ankle stiffness. The advanced mean value method predicted confidence bounds comparable to a 1000-trial Monte Carlo simulation, and required only 14 model evaluations and 4-min processing time. The extended probabilistic simulation may be useful to virtually test new prophylactic strategies for ankle sprains, and is made available for open-source use (https://simtk.org/projects/sprain-sim).

Within-Session Reliability and Minimum Detectable Differences for Discrete Lower-Extremity Angles and Moments During Walking.

Differences in walking biomechanics between groups or conditions should be greater than the measurement error to be considered meaningful. Reliability and minimum detectable differences (MDDs) have not been determined for lower-extremity angles and moments during walking within a session, as needed for interpreting differences in cross-sectional studies. Thus, the purpose of this study was to determine within-session reliability and MDDs for peak ankle, knee, and hip angles and moments during walking. Three-dimensional gait analysis was used to record walking at 1.25m/s (±5%) in 18 men, 18-50years of age. Peak angles and moments were calculated for 2 sets of 3 trials. Intraclass correlation coefficients (3, 3) were used to determine within-session reliability. In addition, MDDs were calculated. Within-session reliability was good to excellent for all variables. The MDDs ranged from 0.9° to 3.6° for joint angles and 0.06 to 0.15N·m/kg for joint moments. Within-session reliability for peak ankle, knee, and hip angles and moments was better than the between-session reliability reported previously. Overall, our MDDs were similar or smaller than those previously reported for between-session reliability. The authors recommend using these MDDs to aid in the interpretation of cross-sectional comparisons of lower-extremity biomechanics during walking in healthy men.

Single- Versus Dual-Task Functional Movement Paradigms: A Biomechanical Analysis.

Laboratory-based movement assessments are commonly performed without cognitive stimuli (ie,single-task) despite the simultaneous cognitive processing and movement (ie,dual task) demands required during sport. Cognitive loading may critically alter human movement and be an important consideration for truly assessing functional movement and understanding injury risk in the laboratory, but limited investigations exist. To comprehensively examine and compare kinematics and kinetics between single- and dual-task functional movement among healthy participants while controlling for sex. Cross-sectional study. Laboratory. Patients (or Other Participants): Forty-one healthy, physically active participants (49% female; 22.5 ± 2.1y; 172.5 ± 11.9cm; 71.0 ± 13.7kg) enrolled in and completed the study. All participants completed the functional movement protocol under single- and dual-task (subtracting by 6s or 7s) conditions in a randomized order. Participants jumped forward from a 30-cm tall box and performed (1)maximum vertical jump landings and (2)dominant and (3)nondominant leg, single-leg 45° cuts after landing. The authors used mixed-model analysis of variances (α = .05) to compare peak hip, knee, and ankle joint angles (degrees) and moments (N·m/BW) in the sagittal and frontal planes, and peak vertical ground reaction force (N/BW) and vertical impulse (Ns/BW) between cognitive conditions and sex. Dual-task resulted in greater peak vertical ground reaction force compared with single-task during jump landing (mean difference = 0.06N/BW; 95% confidence interval [CI], 0.01 to 0.12; P = .025) but less force during dominant leg cutting (mean difference = -0.08N/BW; 95% CI, -0.14 to -0.02; P = .015). Less hip-flexion torque occurred during dual task than single task (mean difference = -0.09N/BW; 95% CI, -0.17 to -0.02). No other outcomes were different between single and dual task (P ≥ .053). Slight, but potentially important, kinematic and kinetic differences were observed between single- and dual-task that may have implications for functional movement assessments and injury risk research. More research examining how various cognitive and movement tasks interact to alter functional movement among pathological populations is warranted before clinical implementation.

Does Ankle Exoskeleton Assistance Impair Stability During Walking in Individuals with Cerebral Palsy?

Lower-limb exoskeletons have the potential to improve mobility in individuals with movement disabilities, such as cerebral palsy (CP). The goal of this study was to assess the impact of plantar-flexor assistance from an untethered ankle exoskeleton on dynamic stability during unperturbed and perturbed walking in individuals with CP. Seven participants with CP (Gross Motor Function Classification System levels I-III, ages 6-31years) completed a treadmill walking protocol under their normal walking condition and while wearing an ankle exoskeleton that provided adaptive plantar-flexor assistance. Pseudo-randomized treadmill perturbations were delivered during stance phase by accelerating one side of a split-belt treadmill. Treadmill perturbations resulted in a significant decrease in anteroposterior minimum margin-of-stability (-32.1%, p < 0.001), and a significant increase in contralateral limb step length (8.1%, p = 0.005), integrated soleus activity during unassisted walking (23.4%, p = 0.02), and peak biological ankle moment (9.6%, p = 0.03) during stance phase. Plantar-flexor assistance did not significantly alter margin-of-stability, step length, soleus activity, or ankle moments during both unperturbed and perturbed walking. These results indicate that adaptive plantar-flexor assistance from an untethered ankle exoskeleton does not significantly alter dynamic stability maintenance during unperturbed and perturbed walking for individuals with CP, supporting future research in real-world environments.

Acute Effects of Handheld Loading on Standing Broad Jump in Youth Athletes.

The study aimed to investigate the acute effects of handheld loading on standing broad jump (SBJ) performance and biomechanics. Fifteen youth male athletes (mean age: 14.7 ± 0.9 years; body mass: 59.3 ± 8.0 kg; height: 1.73 ± 0.07 m) volunteered to participate in the study. Participants were assigned to perform SBJ with and without 4 kg dumbbells in a random order. Kinematic and kinetic data were collected using 10 infrared high-speed motion-capture cameras at a 250 Hz sampling rate and two force platforms at a 1000 Hz sampling rate. A paired t-test was applied to all variables to determine the significance between loading and unloading SBJs. Horizontal distance (p < 0.001), take-off distance (p = 0.001), landing distance (p < 0.001), horizontal velocity of center of mass (CoM; p < 0.001), push time (p < 0.001), vertical impulse (p = 0.003), and peak horizontal and vertical ground reaction force (GRF; p < 0.001, p = 0.017) were significantly greater in loading SBJ than in unloading SBJ. The take-off vertical velocity of CoM (p = 0.001), take-off angle (p < 0.001), peak knee and hip velocity (p < 0.001, p = 0.007), peak ankle and hip moment (p = 0.006, p = 0.011), and peak hip power (p = 0.014) were significantly greater in unloading SBJ than in loading SBJ. Conclusions: Acute enhancement in SBJ performance was observed with handheld loading. The present findings contribute to the understanding of biomechanical differences in SBJ performance with handheld loading and are highly applicable to strength and conditioning training for athletes.

Differences in stride length and lower limb moments of recreational runners during over-ground running while barefoot, in minimalist and in maximalist running shoes

The aim of this study was to compare stride length, and peak knee and ankle moments during over-ground running performed barefoot, in minimalist and in maximalist shoes. Fifteen (10 male, 5 female) recreational endurance runners who habitually wore conventional-cushioned shoes participated. Stride length, as well as knee and ankle moments, were recorded during running on an indoor runway at a self-selected comfortable speed while barefoot, in minimalist and in maximalist shoes. Each condition was performed on a different day and the order of conditions was randomised and counterbalanced. Differences in stride length, and peak knee and ankle moments between conditions were examined with ANCOVA with speed as the covariate. After adjusting for speed, there was a significant increase in stride length from barefoot (1.85 ± 0.01 m) to minimalist (1.91 ± 0.01 m) to maximalist shoes (1.95 ± 0.01 m). Peak knee flexion moment also increased significantly from barefoot (2.51 ± 0.06 Nm⋅kg−1) to minimalist (2.67 ± 0.06 Nm⋅kg−1) to maximalist shoes (2.81 ± 0.06 Nm⋅kg−1). Results then showed peak dorsiflexion moment was lower in the maximalist condition (2.34 ± 0.04 Nm⋅kg−1) than both the barefoot (2.57 ± 0.04 Nm⋅kg−1) and minimalist condition (2.66 ± 0.03 Nm⋅kg−1). Results suggest that stride length and peak knee flexion moment increase from barefoot to minimalist to maximalist shoes, and ankle moment significantly changes as a function of footwear. This indicates that footwear can influence self-selected stride length and peak lower limb loads that are a risk factor for running-related knee injury.

Lower extremity stiffness in habitual forefoot strikers during running on different overground surfaces

Sports surface is one of the known external factors affecting running performance and injury. To date, we have found no study that examined the lower extremity stiffness in habitual forefoot strikers running on different overground surfaces. Therefore, the objective of this study was to investigate lower extremity stiffness and relevant kinematic adjustments in habitual forefoot strikers while running on different surfaces. Thirty-one male habitual forefoot strikers were recruited in this study. Runners were instructed to run at a speed of 3.3 m/s (±5%) on three surfaces, named synthetic rubber, concrete, and artificial grass. No significant differences were found in leg stiffness, vertical stiffness, and joint stiffness in the sagittal plane during running on the three surfaces ( p > 0.05). Running on artificial grass exerted a greater displacement in knee joint angle than running on synthetic rubber ( p = 0.002, 95% CI = 1.52-7.35 degrees) and concrete ( p = 0.006, 95% CI = 1.04-7.25 degrees). In the sagittal plane, peak knee moment was lower on concrete than on artificial grass ( p = 0.003, 95% CI = 0.11-0.58 Nm/kg), whereas peak ankle moment was lower on synthetic rubber than on concrete ( p < 0.001, 95% CI = 0.03-0.07 Nm/kg) and on artificial grass ( p < 0.001, 95% CI = 0.02-0.06 Nm/kg). Among the three surfaces, the maximal ground reaction forces on concrete were the lowest ( p < 0.05). This study indicated that running surfaces cannot influence lower extremity stiffness in habitual forefoot strikers at current running speed. Kinematic adjustments of knee and ankle, as well as ground reaction forces, may contribute to maintaining similar lower extremity stiffness.

Lower-limb joint kinetics in jump rope skills performed by competitive athletes

ABSTRACT The purpose of this study was to characterise lower-limb joint kinetics during consecutive double unders and speed step sprints performed by competitive jump rope athletes, and to compare these measurements to running. Sixteen adolescent competitive jump rope athletes performed consecutive double under, speed step, and running trials while motion capture and ground reaction force data were collected. Lower-limb joint moments, power, and work were calculated using an inverse dynamics approach and discrete measurements were compared between skills. Peak ground reaction forces were similar between movements; however, knee and hip joint kinetics were distributed differently between double unders and speed step. In general, double unders were characterised by an increased reliance on knee joint kinetics, while speed step was characterised by an increased reliance on hip joint kinetics. Peak ankle moments were 9–20% greater in speed step when compared to double unders and running (p ≤ 0.050), and peak negative ankle power was 39–114% greater in double unders and speed step when compared to running (p ≤ 0.002). These findings may have important implications for injury risk and load management in jump rope athletes or other individuals that incorporate jump rope into their training programs.

Effects of Horizontal Impeding Force Gait Training on Older Adult Push-Off Intensity.

Aging and many gait pathologies are often characterized by deficits in push-off intensity (i.e., propulsive ground reaction forces and peak ankle moment and power output) during walking. Unfortunately, conventional interventions such as progressive resistance training, designed to enhance calf muscle mechanical output, generally fail to translate strength gains to functional improvements in habitual push-off intensity. Horizontal impeding forces applied to the body's center of mass systematically augment the mechanical output required from muscle-tendon units spanning the ankle during the push-off phase of walking, which could convey long-term benefits via training. Therefore, the purpose of this study was to investigate the preliminary efficacy of a 6-wk horizontal impeding force training paradigm on improving habitual push-off intensity in 11 healthy but not physically active older adults (age = 76 ± 4 yr, 6 females and 5 males). We found that older adults significantly (P < 0.05) increased measures of isometric strength by 18%, maximum walking speed by 10%, and 6-min walk test distance by 9% as a result of horizontal impeding force training. As a more clinically significant contribution of this work, we found that those subjects also increased habitual peak ankle moment and peak ankle power during push off after training by a significant 10% and 15%, respectively (P ≤ 0.036). We conclude that the use of horizontal impeding forces in older adults improves their maximum muscular and walking capacities while encouraging access to newfound strength gains, thereby improving habitual push-off intensity during walking.