Ankle kinematics,center of pressure progression,and lower extremity muscle activity during a side-cutting task in participants with and without chronic ankle instability

This study assessed ankle kinematics, surface electromyography, and center-of-pressure (COP) progression relative to the medial border of the foot during a side-cutting task in individuals with and without chronic ankle instability (CAI). Thirty participants (CAI = 15; Controls = 15) performed a side-cutting task on a force platform while 3-dimentional ankle kinematics, COP position, and surface electromyography from the tibialis anterior, medial gastrocnemius, fibularis longus, fibularis brevis, vastus medialis, and semitendinosus were recorded on the testing leg. Ankle kinematics, root-mean-square muscle activity and COP position relative to the medial boarder of the foot were compared between CAI and healthy controls (p < 0.05). Significantly greater ankle internal rotation from 35–54% of the stance phase (p = 0.032) was found for the CAI group compared to controls. Furthermore, significantly greater tibialis anterior muscle activity from 86–94% of the stance phase (p = 0.022) and a more medial COP position from 81–100% (p < 0.05) and of the stance phase was also observed in the CAI group. Less lateral COP progression and increased tibialis anterior activation in the CAI group could reflect a protective movement strategy during anticipated side-cutting to avoid recurrent injury. However, greater ankle internal rotation during mid-stance highlights a potential ‘giving way’ mechanism in individuals with CAI.     

Cryotherapy and ankle bracing effects on peroneus longus response during sudden inversion

Cryotherapy and ankle bracing are often used in conjunction as a treatment for ankle injury. No studies have evaluated the combined effect of these treatments on reflex responses during inversion perturbation. This study examined the combined influence of ankle bracing and joint cooling on peroneus longus (PL) muscle response during ankle inversion. A 2 × 2 RM factorial design guided this study; the independent variables were: ankle brace condition (lace-up brace, control), and treatment (ice, control), and the dependent variables studied were PL stretch reflex latency (ms), and PL stretch reflex amplitude (% of max). Twenty-four healthy participants completed 5 trials of a sudden inversion perturbation to the ankle/foot complex under each ankle brace and cryotherapy treatment condition. No two-way interaction was observed between ankle brace and treatment conditions on PL latency (P = 0.283) and amplitude (P = 0.884). The ankle brace condition did not differ from control on PL latency and amplitude. Cooling the ankle joint did not alter PL latency or amplitude compared to the no-ice treatment. Ankle bracing combined with joint cooling does not have a deleterious effect on dynamic ankle joint stabilization during an inversion perturbation in normal subjects.     

A laboratory captured ‘giving way’ episode during a single-leg landing task in an individual with unilateral chronic ankle instability

An episode of ‘giving way’ at the ankle is described as excessive inversion of the rearfoot that does not result in an acute ankle sprain and is a unique feature associated with chronic ankle instability (CAI). Limited data currently exists describing the preparatory movement patterns and those that occur during an episode of ‘giving way. Therefore, this case report describes the movement patterns and the forces generated during an unintentional ‘giving way’ captured while an individual with unilateral CAI was performing a single-leg landing task in a research laboratory. The participant completed five single-leg landing trials for both limbs. 3D lower extremity kinematics and kinetics for the sagittal and frontal plane were extracted from 200 ms before and after initial contact (IC). Relative to the affected and un-affected single-leg landing trials, the ‘giving way’ episode was characterized by an increase in plantarflexion and hip extension moments before and after IC. The plantarflexion deviation dissipated (50 ms post-IC) and was followed by excessive ankle inversion. The ankle began to plantarflex again (150 ms post-IC) and the knee extended (50 ms post-IC) and adducted (100 ms post-IC). As a result, the ankle inversion angle plateaued at 150 ms post-IC. Furthermore, large sagittal plane internal joint moments were observed. In the frontal plane, the ‘giving way’ trial generated a large inversion joint moment which was counteracted by a large internal eversion joint moment. The observed plantarflexion and knee extension and adduction after initial contact likely contributed to preventing the ankle from continuing to invert and avoid an ankle sprain.     

Neural excitability of lower extremity musculature in individuals with and without chronic ankle instability: A systematic review and meta-analysis

This systematic review and meta-analysis examined differences in lower extremity neural excitability between ankles with and without chronic ankle instability (CAI). We searched the literature for studies that compared corticomotor or spinal reflexive excitability between a CAI group and controls or copers, or between limbs of a CAI group. Random effects meta-analyses calculated pooled effect sizes for each outcome. Nineteen studies were included. Meta-analyses of motor thresholds of the fibularis longus (Z = 1.17, P = 0.24) and soleus (Z = 0.47, P = 0.64) exhibited no differences between ankles with and without CAI. Pooled data indicate that ankles with CAI had reduced soleus spinal reflexive excitability (Z = 2.18, P = 0.03) and significantly less modulation of the soleus (Z = 6.96, P < 0.01) and fibularis longus (Z = 4.75, P < 0.01) spinal reflexive excitability when transitioning to more challenging stances. Pre-synaptic inhibition was facilitated in ankles with CAI (Z = 4.05, P < 0.01), but no difference in recurrent inhibition existed (Z = 1.50, P = 0.13). Soleus spinal reflexive activity is reduced in those with CAI. Reduced ability of ankles with CAI to modulate soleus and fibularis longus reflexive activity may contribute to impaired balance.     

The effects of joint hypermobility syndrome on the kinematics and kinetics of the vertical jump test

PurposeBiomechanical impairments are not apparent during walking in people with Joint Hypermobility Syndrome (JHS). This research explored biomechanical alterations during a higher intensity task, vertical jumping.Materials and methodsThis cross-sectional study compared a JHS group (n = 29) to a healthy control group (n = 30). Joint kinematics and kinetics were recorded using a Qualisys motion capture system synchronized with a Kistler platform. Independent sample t-tests and standardised mean differences (SMD) were used for statistical analysis.ResultsNo significant statistical or clinical differences were found between groups in joint kinematics and jump height (p ≥ 0.01). Sagittal hip and knee peak power generation were statistically lower in the JHS group during the compression phase (p ≤ 0.01), but not clinically relevant (SMD < 0.5). Clinically relevant reductions were found in the JHS group knee and ankle peak moments during the compression phase, and hip and knee peak power generation during the push phase (SMD ≥ 0.5), although these were not statistically significant (p ≥ 0.01).ConclusionThe JHS group achieved a similar jump height but with some biomechanical alterations. Further understanding of the joint biomechanical behavior could help to optimize management strategies for JHS, potentially focusing on neuromuscular control and strength/power training.     

Loading and knee flexion after stroke: Less does not equal more

It is believed that force feedback can modulate lower extremity extensor activity during gait. The purpose of this research was to determine the role of limb loading on knee extensor excitability during the late stance/early swing phase of gait in persons post-stroke. Ten subjects with chronic hemiparesis post-stroke participated in (1) seated isolated quadriceps reflex testing with ankle loads of 0–0.4N m/kg and (2) gait analysis on a treadmill with 0%, 20% or 40% body weight support. Muscle reflex responses were recorded from vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) during seated testing. Knee kinematics and quadriceps activity during late stance/early swing phase of gait were compared across loading conditions. Although isolated loading of the ankle plantarflexors at 0.2 N m/kg reduced VM prolonged response (p = 0.04), loading did not alter any other measure of quadriceps excitability (all p > 0.08). During gait, the use of BWS did not influence knee kinematics (p = 0.18) or muscle activity (all p > 0.17) during late stance/early swing phase. This information suggests that load sensed at the ankle has minimal effect on the ipsilateral quadriceps of individuals post-stroke during late stance. It appears that adjusting limb loading during rehabilitation may not be an effective tool to address stiff-knee gait following stroke.     

Differences in motor unit behavior during isometric contractions in patients with diabetic peripheral neuropathy at various disease severities

The aim of this study was to determine whether HD-sEMG is sensitive to detecting changes in motor unit behavior amongst healthy adults and type 2 diabetes mellitus (T2DM) patients presenting diabetic peripheral neuropathy (DPN) at different levels. Healthy control subjects (CON, n = 8) and T2DM patients presenting no DPN symptoms (ABS, n = 8), moderate DPN (MOD, n = 18), and severe DPN (SEV, n = 12) performed isometric ankle dorsiflexion at 30 % maximum voluntary contraction while high-density surface EMG (HD-sEMG) was recorded from the tibialis anterior muscle. HD-sEMG signals were decomposed, providing estimates of discharge rate, motor unit conduction velocity (MUCV), and motor unit territory area (MUTA). As a result, the ABS group presented reduced MUCV compared to CON. The groups with diabetes presented significantly larger MUTA compared to the CON group (p < 0.01), and the SEV group presented a significantly lower discharge rate compared to CON and ABS (p < 0.01). In addition, the SEV group presented significantly higher CoV_force compared to CON and MOD. These results support the use of HD-SEMG as a method to detect peripheral and central changes related to DPN.     

Joint kinetic response during unexpectedly reduced plantar flexor torque provided by a robotic ankle exoskeleton during walking

During human walking, plantar flexor activation in late stance helps to generate a stable and economical gait pattern. Because plantar flexor activation is highly mediated by proprioceptive feedback, the nervous system must modulate reflex pathways to meet the mechanical requirements of gait. The purpose of this study was to quantify ankle joint mechanical output of the plantar flexor stretch reflex response during a novel unexpected gait perturbation. We used a robotic ankle exoskeleton to mechanically amplify the ankle torque output resulting from soleus muscle activation. We recorded lower-body kinematics, ground reaction forces, and electromyography during steady-state walking and during randomly perturbed steps when the exoskeleton assistance was unexpectedly turned off. We also measured soleus Hoffmann- (H-) reflexes at late stance during the two conditions. Subjects reacted to the unexpectedly decreased exoskeleton assistance by greatly increasing soleus muscle activity about 60 ms after ankle angle deviated from the control condition (p<0.001). There were large differences in ankle kinematic and electromyography patterns for the perturbed and control steps, but the total ankle moment was almost identical for the two conditions (p=0.13). The ratio of soleus H-reflex amplitude to background electromyography was not significantly different between the two conditions (p=0.4). This is the first study to show that the nervous system chooses reflex responses during human walking such that invariant ankle joint moment patterns are maintained during perturbations. Our findings are particularly useful for the development of neuromusculoskeletal computer simulations of human walking that need to adjust reflex gains appropriately for biomechanical analyses.     

Kinematics and muscle activity when running in partial minimalist,traditional, and maximalist shoes

While several studies have examined kinematic and kinetic differences between maximalist (MAX), traditional (TRAD), or partial minimalist (PMIN) shoes, to date it is unknown how MAX shoes influence muscle activity. This study compared lower extremity kinematics and muscle activity when running in PMIN, TRAD, and MAX shoes. Thirteen participants ran in each shoe while whole body kinematics were recorded using motion capture and electromyography was recorded from seven leg muscles. Differences in kinematics and root mean square amplitudes (RMS) were compared between shoe conditions. There were small differences in sagittal and frontal plane ankle kinematics between shoe conditions, with the MAX shoes resulting in less dorsiflexion at foot strike (p = .002) and less peak dorsiflexion (p < .001), and the PMIN shoes resulting in greater peak eversion (p = .012). Gluteus medius (p.006) and peroneus longus (p = .007) RMS amplitudes were greater in the MAX shoe then the TRAD or PMIN shoes while tibialis anterior RMS amplitudes were higher in the PMIN shoes (p = .005) than either the TRAD or MAX shoes. Consistent with previous findings, these results suggest there are small differences in kinematics when running in these three shoe types. This may partly be explained by the changes in muscle activity, which may be a response in order to maintain a preferred or habitual movement path. Implications for these difference in muscle activity in terms of fatigue or injury remain to be determined.     

The effect of leg dominance and landing height on ACL loading among female athletes

Female athletes are more prone to anterior cruciate ligament (ACL) injury. A neuromuscular imbalance called leg dominance may provide a biomechanical explanation. Therefore, the purpose of this study was to compare the side-to-side lower limb differences in movement patterns, muscle forces and ACL forces during a single-leg drop-landing task from two different heights. We hypothesized that there will be significant differences in lower limb movement patterns (kinematics), muscle forces and ACL loading between the dominant and non-dominant limbs. Further, we hypothesized that significant differences between limbs will be present when participants land from a greater drop-landing height. Eight recreational female participants performed dominant and non-dominant single-leg drop landings from 30 to 60 cm. OpenSim software was used to develop participant-specific musculoskeletal models and to calculate muscle forces. We also predicted ACL loading using our previously established method. There were no significant differences between dominant and non-dominant leg landing except in ankle dorsiflexion and GMED muscle forces at peak GRF. Landing from a greater height resulted in significant differences among most kinetics and kinematics variables and ACL forces. Minimal differences in lower-limb muscle forces and ACL loading between the dominant and non-dominant legs during single-leg landing may suggest similar risk of injury across limbs in this cohort. Further research is required to confirm whether limb dominance may play an important role in the higher incidence of ACL injury in female athletes with larger and sport-specific cohorts.     

Utilization of poultry litter pellets in meat goat diets

Forty-eight crossbred meat goats were used to determine if poultry litter pellets could be used as a protein source in the diets of growing meat goats. Goats were fed one of three 19–21% CP diets containing 0 (CON; n = 18), 20% (20PL; n = 12) or 40% poultry litter pellets (40PL; n = 18). In Experiment 1, 38 animals (n = 13 CON; n = 12 20PL; n = 13 40PL) were used. Goats were allowed a 23-day adjustment period and body weight (BW) and feed intake were measured every 7 days for 42 days. In Experiment 2, 10 males fed CON or 40PL (n = 5 per diet) were used in two metabolism trials at 93.7 ± 0.9 (Trial 1) and 121.7 ± 0.9 d of age (Trial 2). Goats were placed in metabolism crates and after a 3-day adjustment period, feed intake and fecal and urine output were measured and sampled daily for 7 days to determine diet digestibility. In Experiment 1, ADG (79 ± 8 g) and feed efficiency (130 ± 12 g per kg) were not influenced by diet. In Experiment 2, for both trials, organic matter and CP digestibility were similar between diets (80 ± 1 and 70 ± 3% for Trial 1, respectively and 63 ± 2 and 75 ± 7% for Trial 2, respectively). Dry matter digestibility was greater (P < 0.05) for CON (81 ± 1 and 82 ± 1% for Trials 1 and 2, respectively) when compared to 40PL (77 ± 1 and 75 ± 1% for Trials 1 and 2, respectively). The ADF (41 ± 4% for CON and 67 ± 4% for 40PL) and NDF (48 ± 4% for CON and 71 ± 4% for 40PL) were greater (P < 0.01) for 40PL compared to CON diet in Trial 1 only. Digestibility (GE) was higher (P < 0.05) for 40PL (83 ± 0.3%) compared to CON (82 ± 0.3%) in Trial 2 only. The poultry litter pellets may be used effectively as a short-term feedstuff for meat goats.     

Differences in proprioception,muscle force control and comfort between conventional and new-generation knee and ankle orthoses

The aim of this study was to compare muscle force control and proprioception between conventional and new-generation experimental orthoses. Sixteen healthy subjects participated in a single-blind controlled trial in which two different types of orthosis were applied to the dominant knee or ankle, while the following variables were evaluated: muscle force control (accuracy), joint position sense, kinesthesia, static balance as well as subjective outcomes. The use of experimental orthoses resulted in better force accuracy during isometric knee extensions compared to conventional orthoses (P = 0.005). Moreover, the use of experimental orthoses resulted in better force accuracy during concentric (P = 0.010) and eccentric (P = 0.014) ankle plantar flexions and better knee joint kinesthesia in the flexed position (P = 0.004) compared to conventional orthoses. Subjective comfort (P < 0.001) and preference scores were higher with experimental orthoses compared to conventional ones. In conclusion, orthosis type affected static and dynamic muscle force control, kinesthesia, and perceived comfort in healthy subjects. New-generation experimental knee and ankle orthoses may thus be recommended for prophylactic joint bracing during physical activity and to improve the compliance for orthosis use, particularly in patients who require long-term bracing.     

Reduced plantar-flexors extensibility but improved selective motor control associated with age in young children with unilateral cerebral palsy and equinovalgus gait

BackgroundChildren with spastic cerebral palsy gradually lose muscle extensibility but the interplay between the muscular and neurological components of the condition is unclear especially in the pathophysiology of equinovalgus gait.AimThis study aimed to quantify the muscular and neurological disorders in young children with unilateral cerebral palsy, and to investigate the role of the peroneus longus (PL) in equinovalgus gait.Design, setting and population: This was an observational study with prospective assessments of 31 children (median age: 2.9 years, range: 2–6) from outpatient clinic in a tertiary teaching hospital.MethodsClinical measures of plantar flexor extensibility (X_V1), stretch response (X_V3), and active ankle dorsiflexion angle (X_A) were obtained as well as walking velocity and electromyography of tibialis anterior (TA), gastrocnemius medialis (GM) and PL during walking.ResultsWe found reduced extensibility of the triceps surae on the paretic side (effect size r = 0.73, p < 0.001 for soleus and r = 0.68, p < 0.001 for gastrocnemius) and a correlation between reduced triceps surae extensibility and earlier stretch response (ρ = 0.5, p = 0.004). During the swing phase, there was major co-contraction between TA and GM/PL, and significantly larger activation of PL compared to GM (r = 0.46, p = 0.011). Both GM and PL activation decreased with age.ConclusionsOur results suggest gradual deterioration of the muscular disorder and a link between the muscular and neurological disorders, although plantar flexor co-contraction improved with age. The PL was more activated than the GM and may be considered an intervention target to treat equinovalgus gait.     

Effects of repeated ankle plantar-flexions on H-reflex and body sway during standing

The study investigated relations between effects of repeated ankle plantar-flexion movements exercise on the soleus Hoffmann (H) reflex and on postural body sway when maintaining upright stance. Ten young volunteers performed five sets of ankle plantar-flexions of both lower limbs. Assessment of the feet centre-of-pressure (COP) displacement and H-reflex tests were carried out in quiet stance before, during and after the exercise. H-max and M-max responses were obtained in 8 subjects and reported as the peak-to-peak amplitudes of the right soleus muscle electromyographic waves. Mean dispersion of COP along the antero-posterior direction increased significantly during the exercise; whilst the overall H-reflex response indicated a reduction without a concomitant modification in the M-max response. H-reflex responses, however, varied between participants during the first sets of exercise, showing two main trends of modulation: either depression or early facilitation followed by reduction of the H-reflex amplitude. The extent of reflex modulation in standing position was correlated to the concentric work performed during the exercise (r = 0.85; p < 0.01), but not to the antero-posterior COP dispersion. These results suggest that during a repeated ankle plantar-flexions exercise, modulation of the H-reflex measured in upright stance differs across individuals and is not related to changes of postural sway.     

Load Dependency of Postural Control - Kinematic and Neuromuscular Changes in Response to over and under Load Conditions

Introduction

Load variation is associated with changes in joint torque and compensatory reflex activation and thus, has a considerable impact on balance control. Previous studies dealing with over (OL) and under loading (UL) used water buoyancy or additional weight with the side effects of increased friction and inertia, resulting in substantially modified test paradigms. The purpose of this study was to identify gravity-induced load dependency of postural control in comparable experimental conditions and to determine the underlying neuromuscular mechanisms.

Methods

Balance performance was recorded under normal loading (NL, 1g), UL (0.16g; 0.38g) and OL (1.8g) in monopedal stance. Center of pressure (COP) displacement and frequency distribution (low 0.15-0.5Hz (LF), medium 0.5-2Hz (MF), high 2-6Hz (HF)) as well as ankle, knee and hip joint kinematics were assessed. Soleus spinal excitability was determined by H/M-recruitment curves (H/M-ratios).

Results

Compared to NL, OL caused an increase in ankle joint excursion, COP HF domain and H/M-ratio. Concomitantly, hip joint excursion and COP LF decreased. Compared to NL, UL caused modulations in the opposite direction: UL decreased ankle joint excursions, COP HF and H/M-ratio. Collaterally, hip joint excursion and COP LF increased. COP was augmented both in UL and in OL compared to NL.

Conclusion

Subjects achieved postural stability in OL and UL with greater difficulty compared to NL. Reduced postural control was accompanied by modified balance strategies and compensatory reflex activation. With increasing load, a shift from hip to ankle strategy was observed. Accompanying, COP frequency distribution shifted from LF to HF and spinal excitability was enhanced. It is suggested that in OL, augmented ankle joint torques are compensated by quick reflex-induced postural reactions in distal muscles. Contrarily, UL is associated with diminished joint torques and thus, postural equilibrium may be controlled by the proximal segments to adjust the center of gravity above the base of support.     

Influence of ankle functional instability on the ankle electromyography during landing after volleyball blocking

The purpose of this study was to describe, interpret and compare the EMG activation patterns of ankle muscles – tibialis anterior (TA), peroneus longus (PL) and gastrocnemius lateralis (GL) – in volleyball players with and without ankle functional instability (FI) during landing after the blocking movement. Twenty-one players with FI (IG) and 19 controls (CG) were studied. The cycle of movement analyzed was the time period between 200 ms before and 200 ms after the time of impact determined by ground reaction forces. The variables were analyzed for two different phases: pre-landing (200 ms before impact) and post-landing (200 ms after impact). The RMS values and the timing of onset activity were calculated for the three studied muscles, in both periods and for both groups. The co-activation index for TA and PL, TA and GL were also calculated. Individuals with FI presented a lower RMS value pre-landing for PL (CG = 43.0 ± 22.0; IG = 26.2 ± 8.4, p < 0.05) and higher RMS value post-landing (CG = 47.5 ± 13.3; IG = 55.8 ± 21.6, p < 0.10). Besides that, in control group PL and GL activated first and simultaneously, and TA presented a later activation, while in subjects with FI all the three muscles activated simultaneously. There were no significant differences between groups for co-activation index. Thus, the rate of contraction between agonist and antagonist muscles is similar for subjects with and without FI but the activation individually was different. Volleyball players with functional instability of the ankle showed altered patterns of the muscles that play an important role in the stabilization of the foot–ankle complex during the performance of the blocking movement, to the detriment of the ligament complex, and this fact could explain the usual complaints in these subjects.     

Joint-specific power production and fatigue during maximal cycling

Cycling power decreases substantially during a maximal cycling trial of just 30 s. It is not known whether movement patterns and joint powers produced at each joint decrease to a similar extent or if each joint exhibits an individual fatigue profile. Changes in movement patterns and/or joint powers associated with overall task fatigue could arise from several different mechanisms or from a complex interplay of these mechanisms. The purpose of this investigation was to determine the changes in movement and power at each joint during a fatiguing cycling trial. Thirteen trained cyclists performed a 30 s maximal cycling trial on an isokinetic cycle ergometer at 120 rpm. Pedal forces and limb kinematics were recorded. Joint powers were calculated using a sagittal plane inverse dynamics model and averaged for the initial, middle, and final three second intervals of the trial, and normalized to initial values. Relative ankle plantar flexion power was significantly less than all other joint actions at the middle interval (51±5% of initial power; p=0.013). Relative ankle plantar flexion power for the final interval (37±3%) was significantly less than the relative knee flexion and hip extension power (p=0.010). Relative knee extension power (41±5%) was significantly less than relative hip extension power (55±4%) during the final three second interval (p=0.045). Knee flexion power (47±5%) did not differ from relative hip extension power (p=0.06). These changes in power were accompanied by a decrease in time spent extending by each joint with fatigue (i.e., decreased duty cycle, p<0.03). While central mechanisms may have played a role across all joints, because the ankle fatigued more than the hip and knee joints, either peripheral muscle fatigue or changes in motor control strategies were identified as the potential mechanisms for joint-specific fatigue during a maximal 30 s cycling trial.     

Ankle kinematics and kinetics during gait in healthy and rheumatoid arthritis post-menopausal women

Objective: In the literature, it is not clear whether rheumatoid arthritis (RA) post-menopausal women have different ankle biomechanical parameters than healthy post-menopausal women. This study aimed to compare the ankle kinematics and kinetics during the gait stance phase of RA post-menopausal women with age-matched healthy post-menopausal women.

Materials and methods: A three-dimensional motion analysis system (9 cameras; 200?Hz) synchronised with a force plate (1000?Hz) was used to assess ankle kinematics and kinetics during barefoot walking at a natural and self-selected speed. A biomechanical model was used to model body segments and joint centres (combined anthropometric measurements and the placement of 39 reflective markers). Thirty-six women (18 RA post-menopausal women and 18 age-matched healthy post-menopausal women) performed 14 valid trials (comprising seven left and seven right footsteps on a force plate). Lower limb muscle mass was evaluated by an octopolar bioimpedance analyser.

Results: RA post-menopausal women yielded a longer stance phase and controlled dorsiflexion sub-phase (p?<?0.001), higher dorsiflexion at the final controlled dorsiflexion sub-phase and lower plantar flexion at toe off (p?<?0.05), lower angular displacements (p?<?0.05), and lower ankle moment of force peak and ankle power peak (p?<?0.001). No intergroup differences were found in lower limb muscle mass.

Conclusions: RA post-menopausal women yielded changes in ankle kinematic and kinetic parameters during the gait stance phase, resulting in a lower capacity to produce ankle moment of force and ankle power during the propulsive gait phase.     

Lower limb joint stiffness and muscle co-contraction adaptations to instability footwear during locomotion

Unstable shoes (US) continually perturb gait which can train the lower limb musculature, but muscle co-contraction and potential joint stiffness strategies are not well understood. A shoe with a randomly perturbing midsole (IM) may enhance these adaptations. This study compares ankle and knee joint stiffness, and ankle muscle co-contraction during walking and running in US, IM and a control shoe in 18 healthy females. Ground reaction forces, three-dimensional kinematics and electromyography of the gastrocnemius medialis and tibialis anterior were recorded. Stiffness was calculated during loading and propulsion, derived from the sagittal joint angle-moment curves. Ankle co-contraction was analysed during pre-activation and stiffness phases. Ankle stiffness reduced and knee stiffness increased during loading in IM and US whilst walking (ankle, knee: p = 0.008, 0.005) and running (p < 0.001; p = 0.002). During propulsion, the opposite joint stiffness re-organisation was found in IM whilst walking (both joints p < 0.001). Ankle co-contraction increased in IM during pre-activation (walking: p = 0.001; running: p < 0.001), and loading whilst walking (p = 0.003), not relating to ankle stiffness. Results identified relative levels of joint stiffness change in unstable shoes, providing new evidence of how stability is maintained at the joint level.     

Methodological considerations of task and shoe wear on joint energetics during landing

To better understand methodological factors that alter landings strategies, we compared sagittal plane joint energetics during the initial landing phase of drop jumps (DJ) vs. drop landings (DL), and when shod vs. barefoot. Surface electromyography, kinematic and kinetic data were obtained on 10 males and 10 females during five consecutive drop landings and five consecutive drop jumps (0.45 m) when shod and when barefoot. Energy absorption was greater in the DJ vs. DL (P = .002), due to increased energy absorption at the hip during the DJ. Joint stiffness/impedance was more affected by shoe condition, where overall stiffness/impedance was greater in shod compared to barefoot conditions (P = .036). Further, hip impedance was greater in shod vs. barefoot for the DL only (via increased peak hip extensor moment in DL), while ankle stiffness was greater in the barefoot vs. shod condition for the DJ only (via decreased joint excursion and increased peak joint moment in DJ vs. DL) (P = .011). DJ and DL place different neuromechanical demands upon the lower extremities, and shoe wear may alter impact forces that modulate stiffness/impedance strategies. The impact of these methodological differences should be considered when comparing landing biomechanics across studies.