Differences in abductor hallucis activity during running in individuals with chronic ankle instability and copers.

BACKGROUND: Assessment of neuromuscular dysfunction following a lateral ankle sprain during running typically focuses on the activities of the extrinsic foot muscles. Although the interaction between intrinsic and extrinsic foot muscles has been reported, there are no studies on the activities of intrinsic foot muscles in individuals with chronic ankle instability and ankle sprain copers. RESEARCH QUESTION: Do copers and individuals with chronic ankle instability (CAI) have different abductor hallucis activity? METHODS: This study included 11 controls, 11 copers, and 16 CAI participants. A wireless surface electromyography system was applied to the abductor hallucis, peroneus longus, tibialis anterior, and medial gastrocnemius muscles. Running was performed on a treadmill (speed of 3.5 m/s). The stance phase is divided into four functional phases. The muscle activities during these phases were calculated using the root mean square standardized by the root mean square during static standing with a double-leg stance. RESULTS: Abductor hallucis activity was significantly lower during most phases in the coper and control groups than in the CAI group (P < 0.05). There were no differences in the extrinsic foot muscles among the groups (P > 0.05). SIGNIFICANCE: Simultaneous investigations of muscle activity in the abductor hallucis and extrinsic foot muscles identified neuromuscular dysfunction after ankle sprains. Increased activity of the abductor hallucis may be associated with recurrent ankle sprains.

Arch height flexibility is associated with plantar fascia tension during running.

BACKGROUND: Plantar fascia tension is considered to cause plantar fasciitis, and medial longitudinal arch decrease is believed to be a risk factor for plantar fasciitis. Arch height index (AHI) and arch height flexibility (AHF) are useful indicators for evaluating medial longitudinal arch. However, the relationship between plantar fascia tension during running and these indicators remain unclear. RESEARCH QUESTION: Are the foot characteristics in AHI and AHF that represent medial longitudinal arch related to plantar fascia tension during running? METHODS: Twenty-two male participants enrolled in this study. Foot characteristics required for calculating AHI and AHF were measured using the AHI measurement system. AHI was defined as the height from the floor to the dorsum of the foot divided by the truncated foot length with 10% or 50% load. AHF was defined as the change in arch height from the 10% and 50% loads. Marker trajectories of the foot and force plate data during running were measured using a three-dimensional motion analysis system and a force plate. Based on the measured data, the peak values of the plantar fascia tension were analyzed. Pearson's correlation was used to determine the relationship between foot characteristics and plantar fascia tension. RESULTS: No significant correlation was found between AHI in the 10% load condition and plantar fascia tension (r = -0.36, p = 0.09) or between AHI in the 50% load condition and plantar fascia tension (r = -0.148, p = 0.515). In contrast, a significant moderate positive correlation was observed between AHF and plantar fascia tension (r = 0.568, p < 0.01). SIGNIFICANCE: AHF is a change in arch height between sitting and standing positions, can be easily used to evaluate plantar fascia tension in clinical settings. This study implies that evaluating AHF is a useful tool in considering plantar fascia tension during running.

Center of Pressure Deviation during Posture Transition in Athletes with Chronic Ankle Instability.

Center of pressure (COP) tracking during posture transition is an ideal scale for determining the recurrence of an ankle injury, thereby preventing chronic ankle instability (CAI). However, the same is difficult to determine because the reduced ability of certain patients (who experienced sprain) to control posture at the ankle joint is masked by the chain of hip and ankle joint motion. Thus, we observed the effects of knee joint immobilization/non-immobilization on postural control strategies during the posture transition task and attempted to evaluate the detailed pathophysiology of CAI. Ten athletes with unilateral CAI were selected. To examine differences in COP trajectories in the CAI side and non-CAI legs, patients stood on both legs for 10 s and one leg for 20 s with/without knee braces. COP acceleration during the transition was significantly higher in the CAI group with a knee brace. The COP transition from the double- to single-leg stance phase was significantly longer in the CAI foot. In the CAI group, the fixation of the knee joint increased COP acceleration during postural deviation. This suggests that there is likely an ankle joint dysfunction in the CAI group that is masked by the hip strategy.

Concurrent validity and reliability of a mobile iOS application used to assess calf raise test kinematics.

BACKGROUND: Calf raise test (CRT) is used in rehabilitation and sports medicine to evaluate calf muscle function. The Calf Raise application (CRapp) uses computer-vision algorithms to objectively measure CRT outcomes and replicate laboratory-based metrics that are difficult to measure clinically. OBJECTIVE: To validate the CRapp by examining its concurrent validity and agreement levels against laboratory-based equipment, and its intra- and inter-rater reliability. DESIGN: Observational cross-sectional validation study. METHODS: CRT outcomes (i.e., repetitions, positive work, total height, peak height, fatigue index, and peak power) were assessed in thirteen individuals (6 males, 7 females) on three occasions on both legs using the CRapp, 3D motion capture, and force plate simultaneously. Data were extracted from two markers: below lateral malleolus (n = 77) and on the heel (n = 77). Concurrent validity and agreement were determined from 154 data files using intraclass correlation coefficients (ICC3,k), typical errors expressed as coefficient of variations (CV), and Bland-Altman plots to assess biases and precision. Reliability was assessed using ICC3,1 and CV values. RESULTS: Validity of CRapp outcomes was good to excellent across measures for both markers (mean ICC ≥0.878), precision plots showing good agreement and precision. CV ranged from 0% (repetitions) to 33.3% (fatigue index) and were on average better for the lateral malleolus marker. Inter- and intra-rater reliability were excellent (ICC≥0.949, CV ≤ 5.6%). CONCLUSION: CRapp is valid and reliable within and between users for measuring CRT outcomes in healthy adults. CRapp provides a tool to objectivise CRT outcomes in research and practice, aligning with recent advances in mobile technologies and their increased use in healthcare.

Differences in the coordination and its variability among foot joints during running in neutral foot and flatfoot.

Flatfoot is a well-known foot deformity, with a prevalence of 11.2%-29.0% among adults. Running injuries can occur in individuals with flatfoot; however, the underlying mechanism remains unknown. We investigated the coordination pattern and variability among foot joints while running by comparing participants with neutral foot and with flatfoot. Participants with neutral foot (n = 15) and flatfoot (n = 15) were asked to run at their preferred speed. Using the modified vector coding technique, the coupling angle between the foot joints, representing interjoint coordination, was calculated and categorized into four coordination patterns. The standard deviation of the coupling angle was computed to measure the coordination variability during the stance phase. There were no differences in the spatiotemporal parameters (speed, step length, and cadence) between the groups. In the sagittal rearfoot and sagittal midfoot coordination patterns, the flatfoot group showed a significantly greater proportion of anti-phase with proximal dominancy and a lower proportion of in-phase with proximal dominancy than the neutral foot group during early stance. Coordination variabilities between the sagittal rearfoot and sagittal midfoot (midstance), between the sagittal midfoot and sagittal forefoot (early stance), and between the frontal rearfoot and sagittal midfoot (midstance) were greater in the flatfoot group than in the neutral foot group. This may explain why those with flatfoot are likely to experience running injuries.

Effect of Arch Height Flexibility in Individuals With Flatfoot on Abductor Hallucis Muscle Activity and Medial Longitudinal Arch Angle During Short Foot Exercises.

Flatfoot presents decreased medial longitudinal arch (MLA), and such foot deformity involves intrinsic foot muscles dysfunction. Flatfoot can be classified into flexible and stiff types according to arch height flexibility (AHF). Short foot exercise (SFE) is an intrinsic foot muscle strengthening exercise, which is reportedly effective against flatfoot. However, its effectiveness against flexible or stiff types in flatfoot is unclear. We examined the effect of AHF in individuals with flatfoot during abductor hallucis muscle (AbH) activity and medial longitudinal arch during SFE. Foot alignment was assessed using the arch height index during standing, and individuals with flatfoot (N = 16) were recruited. The AbH activity and MLA angle during SFE while maintaining single-leg standing were assessed. The relationship between AHF and AbH activity and between AHF and MLA angle ratio was analyzed using correlation coefficients. Additional correlations between AHF and AbH activity were observed with the outliers removed. There were no correlations between AHF and AbH muscle activity and between AHF and MLA angle ratio. However, with the 2 outliers removed, moderate correlations between AHF and AbH activity were significant (r = 0.64, p = .01). AbH activity during SFE increased in individuals with flatfoot for high AHF (flexible type). Thus, SFE may be more effective for individuals with flatfoot having a high AHF. These findings may be helpful when making decisions for surgery and rehabilitation.

Coper has altered foot joint coordination pattern compared to individuals with chronic ankle instability during running.

BACKGROUND: There is limited information regarding the cause for the different etiologies in individuals with initial lateral ankle sprains (LAS) who have chronic ankle instability (CAI) and no recurrence or instability for > 12 months (copers) following initial LAS. Assessing the movement patterns of copers and individuals with CAI and LAS recurrence is essential for identifying the mechanical factors that affect patient outcomes. RESEARCH QUESTION: Does coordination and coordination variability of rearfoot, midfoot, and forefoot present a potentially causative pattern for CAI or coper? METHODS: This cross-sectional study included 35 males who were divided into the CAI (n = 13), coper (n = 12), and control group (n = 10). Participants performed rearfoot strike running on the treadmill at a fixed speed of 3.5 m/s. The coupling angle between the rearfoot, midfoot, and forefoot, representing intersegmental coordination, was calculated using the modified vector coding technique and categorized into four coordination patterns. The coupling angle standard deviation served represented coordination variability during the stance phase. RESULTS: One control participant and one CAI participant were excluded, and final analyses were performed on the CAI (n = 12), coper (n = 12), and control (n = 9) groups. During late stance, the coper group showed a significantly greater proportion of in-phase with distal dominancy (p = 0.02, effect size=0.17) and a significantly lower proportion of in-phase with proximal dominancy (p = 0.05, effect size=0.17), than the CAI group. During the early stance, the coper group showed a significantly lower proportion of anti-phase with distal dominancy than the CAI group (p = 0.03, effect size=0.18). There were no differences in intra-foot variability among the groups. SIGNIFICANCE: The intra-foot coordination observed in the coper group suggests that this movement pattern may reduce the risk of ankle sprains.

Copers exhibit altered ankle and trunk kinematics compared to the individuals with chronic ankle instability during single-leg landing.

Copers are individuals who have had a lateral ankle sprain but have no history of recurrent lateral ankle sprain, residual symptoms, or functional disability. Copers have shown no significant difference in lower limb kinematics in landing for proactive conditions compared with a control (CTR) group. However, the copers (CPR) group has shown differences compared to CTR and chronic ankle instability (CAI) groups for dynamic balance conditions, suggesting that the trunk may compensate for foot instability during shock absorption. This study aimed to examine the differences in the kinematics and kinetics among CPR, CAI and CTR groups in reactive and proactive single-leg landing tasks. Participants were physically active adults with CAI (n = 14), CPR (n = 14), and CTR (n = 14), who performed proactive and reactive single-leg landings. The lower limb, trunk kinematics, vertical ground reaction force (vGRF) peak value, and the time to minimum peak vGRF were analysed. It might be conceivable that the CPR group could absorb vGRF efficiently by increasing the trunk flexion angle and increasing the time to reach the minimum peak vGRF regardless of landing condition. The results suggest that evaluating the movements of the entire body, including the ankle and trunk, is essential.

Infants born preterm demonstrate reduced task-specific exploration during the scaffolded kick-activated mobile task.

This study quantified the spatial exploration of 13 infants born very and extremely preterm (PT) at 4 months corrected age as they learned that moving their feet vertically to cross a virtual threshold activated an infant kick-activated mobile and compared results to 15 infants born full-term (FT) from a previously published study. Spatial exploration was quantified using two general spatial exploration variables (exploration volume, exploration path), two task-specific spatial variables (duration of time in the task-specific region of interest, vertical variance of kicks), and one non-task-specific spatial variable (horizontal variance of kicks). The infants born PT, similar to FT, increased their general spatial exploration and duration in the region of interest and did not change the vertical and horizontal variances of kicks. However, the infants born PT, compared to FT, spent less time in the task-specific region of interest and had a greater non-task-specific horizontal variance throughout the task. This may indicate that infants born PT and FT exhibit similar general spatial exploration, but infants born PT exhibit less task-specific spatial exploration. Future research is necessary to determine the contribution of learning and motor abilities to the differences in task-specific exploration between infants born PT and FT.

Motivating Selective Motor Control of Infants at High Risk of Cerebral Palsy Using an In-Home Kicking-Activated Mobile Task: A Pilot Study.

OBJECTIVE: Decreased selective motor control limits gait function of children with spastic cerebral palsy (CP). Infants at high risk of CP demonstrate decreased selective motor control by 1 month of age. To motivate more selective hip-knee control, infants at high risk of CP participated in an in-home kicking-activated mobile task. The purpose of this study was to determine whether infants at high risk of CP and infants with typical development (TD) demonstrated increased selective hip-knee control during 2-minute intervals of the mobile task when they demonstrated learning of the association between their leg movement and mobile activation vs during 2-minute intervals when they did not demonstrate learning. METHODS: Participants in this cohort study included 10 infants at high risk of CP based on neuroimaging and 11 infants with TD at 3.5 to 4.5 months of age. Each infant participated in the in-home kicking-activated mobile task for 8 to 10 min/d, 5 d/wk, for 6 weeks. Over 80,000 kicks were extracted and classified for each infant as occurring during 2-minute intervals of the task when the infant demonstrated learning vs not learning based on mobile activation time above baseline. RESULTS: Infants demonstrated kicks with more selective hip-knee control during 2-minute intervals of the mobile task when they demonstrated learning compared with when they did not demonstrate learning for 4 of 6 weeks in the cohort at high risk of CP and for 2 of 6 weeks in the cohort with TD. CONCLUSION: Participation in the in-home kicking-activated mobile task may motivate more selective hip-knee control of infants at high risk of CP. IMPACT: This study is a first step toward developing an intervention to promote selective hip-knee control of infants at high risk of CP, with the ultimate goal of optimizing future walking function. LAY SUMMARY: This study showed that playing with an in-home infant kicking-activated mobile may motivate infants at high risk of CP to produce more age-appropriate leg movements.

Copers adopt an altered dynamic postural control compared to individuals with chronic ankle instability and controls in unanticipated single-leg landing.

BACKGROUND: Several prior studies involving "expected" single-leg landings have not succeeded in establishing a difference between copers and a control group. RESEARCH QUESTION: Does expected and unanticipated single-leg landing affect dynamic postural stability in lateral ankle sprain individuals with chronic ankle instability (CAI), copers, and controls? METHODS: In this prospective cross-sectional study, physically active adults with CAI (n = 12), copers (n = 12), and controls (n = 12) were included. Participants performed expected single-leg landing by stepping off a 30-cm box. They also performed unanticipated landings including side-step cutting, side-step cutting at 60°, single-leg landing, and forward stepping. The expected and unanticipated conditions of each groups were compared in terms of time to stabilization (TTS) and center of pressure (COP) for the anterior-posterior (AP) and medial-lateral (ML) conditions. To analyze the data, a mixed-model one-way analysis of variance and a Tukey-Kramer post hoc test were performed. RESULTS: A significant condition × group interaction was observed in only TTS ML, with the CAI group demonstrating a significantly longer TTS ML than the coper (p < 0.001) and control (p < 0.001) groups during unanticipated trials. In addition, group interaction effects were observed for COP AP and TTS AP. The coper group demonstrated significantly longer COP AP and TTS AP than the control group (p < 0.001). SIGNIFICANCE: The CAI group demonstrated a significantly longer TTS ML than the coper and control groups during the unanticipated condition, and the coper group demonstrated significantly longer TTS AP and COP AP than the control group. Thus, longer COP AP and TTS AP sway time in the coper group may be a protection mechanism, allowing greater freedom in the AP plane while quickly controlling ML sway and preventing lateral ankle sprains. These findings can help in the prevention of lateral ankle sprains and assessment of dynamic postural control.

Quantifying Infant Exploratory Learning.

Exploration is considered essential to infant learning, but few studies have quantified infants' task exploration. The purpose of this study was to quantify how infants explored task space with their feet while learning to activate a kick-activated mobile. Data were analyzed from fifteen 4-month-old infants who participated in a 10-min mobile task on 2-3 consecutive days. Infants learned that their vertical leg movements above a systematically increased threshold height activated the mobile. Five kinematic variables were analyzed: 1) exploration space volume, 2) exploration path length, 3) duration of time in the region of interest around the threshold that activated the mobile, 4) task-specific vertical variance of kicks, and 5) non-task-specific horizontal variance of kicks. The infants increased their general spatial exploration, volume and path, and the infants adapted their exploration by maintaining their feet within the region of interest although the task-specific region increased in height as the threshold increased. The infants used task-specific strategies quantified by the increased variance of kicks in the vertical direction and no change in the horizontal variance of kicks. Quantifying infants' task exploration may provide critical insights into how learning emerges in infancy and enable researchers to more systematically describe, interpret, and support learning.

Influence of sex and knee joint rotation on patellofemoral joint stress.

PURPOSE: Females are two times as likely to experience patellofemoral pain syndrome (PFPS) than males, however, the reason for this difference between sexes remains unclear. Patellofemoral joint (PFJ) stress is believed to contribute to PFPS alterations through knee joint rotation alignment, but the influence of knee joint rotation conditions on PFJ stress is unclear. We aimed to investigate the influence of sex and knee joint rotation alignment on PFJ stress. METHODS: Simulation ranges were set to knee joint flexion angles of 10-45° (common to both sexes) and extension moments of 0-240 Nm (males) and 0-220 Nm (females). The quadriceps force and effective lever arm length at the quadriceps muscle were determined as a function of the knee joint flexion angle and extension moment. The PFJ contact area, which is specific to sex, and knee joint rotation were calculated from cadaver data, and PFJ stress was estimated. RESULTS: In all knee joint rotation conditions, PFJ stress was higher in females than in males. Additionally, PFJ stress in males and females was the largest under neutral conditions compared with other rotation conditions. CONCLUSION: The results of the present study may be useful for understanding the underlying mechanisms contributing to the differences in PFPS in males and females.

Effects of step length and cadence on hip moment impulse in the frontal plane during the stance phase.

BACKGROUND: An excessive daily cumulative hip moment in the frontal plane (determined as the product of hip moment impulse in the frontal plane during the stance phase and mean number of steps per day) is a risk factor for the progression of hip osteoarthritis. Moreover, walking speed and step length decrease, whereas cadence increases in patients with hip osteoarthritis. However, the effects of step length and cadence on hip moment impulse in the frontal plane during the stance phase are not known. Therefore, this study aimed to examine the effects of step length and cadence on hip moment impulse in the frontal plane during the stance phase. METHODS: We used a public dataset (kinetic and kinematic data) of over-ground walking and selected 31 participants randomly from the full dataset of 57 participants. The selected participants walked at a self-selected speed and repeated the exercise 15 times. We analyzed the data for all 15 trials for each participant. Multiple regression analysis was performed with the hip moment impulse in the frontal plane during the stance phase as the dependent variable and step length and cadence as independent variables. RESULTS: The adjusted R 2 in this model was 0.71 (p < 0.001). The standardized partial regression coefficients of step length and cadence were 0.63 (t = 5.24; p < 0.001) and -0.60 (t =  - 4.58; p < 0.001), respectively. CONCLUSIONS: Our results suggest that low cadence, not short step length, increases the hip moment impulse in the frontal plane. Our findings help understand the gait pattern with low hip moment impulse in the frontal plane.

Infants born preterm and infants born full-term generate more selective leg joint movement during the scaffolded mobile task.

Infants born very preterm (PT), prior to 32 weeks gestation, are at increased risk of developing cerebral palsy. Children with spastic cerebral palsy have impaired selective leg joint movement, which contributes to lifelong walking limitations. We investigated whether infants born PT generated more selective hip-knee joint movement (e.g., hip flexes as knee extends) while participating in a scaffolded mobile task. Infants born PT and infants born full-term (FT) at 4 months corrected age participated in a scaffolded mobile task for 2-3 consecutive days. The scaffolded mobile task required infants to raise their legs vertically over a virtual threshold. Three threshold heights (low, middle, and high) were used to test whether the middle and high heights encourage infants to move their legs more selectively. Fifteen infants born FT learned the task and showed more selective hip-knee movement at each of the three threshold heights on the day that they learned, compared with their baseline spontaneous kicking. Thirteen infants born PT learned the task and showed more selective hip-knee movement on their learning day, but only when the middle and high thresholds were used. The results show that the scaffolded mobile task effectively encouraged infants to generate more selective hip-knee joint movement.

Spinal movement variability associated with low back pain: A scoping review.

OBJECTIVE: To identify suggestions for future research on spinal movement variability (SMV) in individuals with low back pain (LBP) by investigating (1) the methodologies and statistical tools used to assess SMV; (2) characteristics that influence the direction of change in SMV; (3) the methodological quality and potential biases in the published studies; and (4) strategies for optimizing SMV in LBP patients. METHODS: We searched literature databases (CENTRAL, Medline, PubMed, Embase, and CINAHL) and comprehensively reviewed the relevant papers up to 5 May 2020. Eligibility criteria included studies investigating SMV in LBP subjects by measuring trunk angle using motion capture devices during voluntary repeated trunk movements in any plane. The Newcastle-Ottawa risk of bias tool was used for data quality assessment. Results were reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews. RESULTS: Eighteen studies were included: 14 cross-sectional and 4 prospective studies. Seven linear and non-linear statistical tools were used. Common movement tasks included trunk forward bending and backward return, and object lifting. Study results on SMV changes associated with LBP were inconsistent. Two of the three interventional studies reported changes in SMV, one of which was a randomized controlled trial (RCT) involving neuromuscular exercise interventions. Many studies did not account for the potential risk of selection bias in the LBP population. CONCLUSION: Designers of future studies should recognize that each of the two types of statistical tools assesses functionally different aspects of SMV. Future studies should also consider dividing participants into subgroups according to LBP characteristics, as three potential subgroups with different SMV characteristics were proposed in our study. Different task demands also produced different effects. We found preliminary evidence in a RCT that neuromuscular exercises could modify SMV, suggesting a rationale for well-designed RCTs involving neuromuscular exercise interventions in future studies.

Individuals with chronic ankle instability exhibit altered ankle kinematics and neuromuscular control compared to copers during inversion single-leg landing.

OBJECTIVES: This study compares the ankle kinematics and muscle activities of the individuals with chronic ankle instability (CAI), coper, and control groups in normal and inversion single-leg landings. DESIGN: cross-sectional study; SETTING: Biomechanics laboratory. PARTICIPANTS: Physically active adults with CAI (N = 12); and coper (N = 12) and control (N = 12) groups. MAIN OUTCOME MEASURES: The participants performed normal and inversion single-leg landing. The muscle activity 200 ms before and after landing of the tibialis anterior, the medial gastrocnemius, and the fibularis longus (FL) were recorded. The FL latency, sagittal and frontal co-contraction indexes (CCI), ankle inversion angle at the initial contact, and the maximum inversion angle were recorded. RESULTS: Significantly longer FL latency, decreased FL muscle activity, frontal CCI, and an increased maximum inversion angle at post-landing were discovered during inversion single-leg landing in the CAI group compared to the coper and control groups. However, no significant difference was observed among the CAI and coper groups during normal single-leg landing. CONCLUSION: These results suggest prolonged FL latency and altered ankle kinematics suggest an increased risk of recurrent lateral ankle sprains in CAI with inversion single-leg landing.

Copers adopt an altered movement pattern compared to individuals with chronic ankle instability and control groups in unexpected single-leg landing and cutting task.

Individuals with chronic ankle instability (CAI) demonstrate altered ankle kinematics during landing compared to uninjured individuals. However, if copers may have adopted unique movement strategy to prevent repeated ankle sprains is unclear. The purpose of this study compares the lower-extremity joint kinematics and muscle activities of CAI (N = 8), coper (COP) (N = 8), and control (CON) (N = 8) groups in unexpected single-leg landing and cutting. Performance time (from initial contact to toe-off), number of mistakes in the jumping direction, low-extremity joint angle are assessed. Muscle activities were recorded from the tibialis anterior, medial gastrocnemius, and peroneus longus (PL), and mean muscle activity, co-contraction index (CI), and PL latency were analyzed. Results of performance time and CI are not significant. Significantly less number of mistakes in the jumping direction and a shorter PL latency were discovered in the COP and CON compared with the CAI group (P < 0.05). The peak hip joint flexion angle is significantly smaller in the COP than in the CON (P = 0.04). In dynamic tasks requiring quick judgments of ankle inclination, the COP may be able to accurately sense the inclination of the foot. Additionally, movement strategies differed between the COP and CON groups in an unexpected single-leg landing and cutting.

Shank and rearfoot coordination and its variability during running in flatfoot.

Flatfoot is a risk factor for patellofemoral pain syndrome (PFPS), and excessive rearfoot eversion occurring in flatfoot has been associated with the development and progression of PFPS; however, the mechanism remains unclear. This study aimed to investigate transverse shank and frontal rearfoot coordination patterns and variability when running with normal foot and flatfoot. Participants with normal foot (n = 13) and flatfoot (n = 13) were asked to run at their preferred speed. The coupling angle between the shank and rearfoot, representing intersegmental coordination, was calculated using the modified vector coding technique and categorized into four coordination patterns. Standard deviation of the coupling angle was computed as a measure of coordination variability during the stance phase. No differences in the characteristics and spatiotemporal parameters between groups were found, and all participants had rearfoot strike pattern. During midstance, the flatfoot group showed a significantly greater proportion of anti-phase with proximal (shank) dominancy than the normal foot group (p = 0.04, effect size = 0.88 [large]). Furthermore, flatfoot group showed a significantly greater in variability than the normal foot group (p = 0.03, effect size = 0.91 [large]). This study's results may help explain why flatfoot is likely to result in PFPS. However, the occurrence mechanism of running injuries like PFPS is multi- factorial. Since these results alone are not sufficient to explain the cause-effect relationship between flatfoot and injuries like PFPS, a prospective study including other factors such as patellofemoral joint stress would also be needed.

Infants born full term and preterm increase the height of anti-gravity leg movements during a kick-activated mobile task using a scaffolded task environment.

Prior research supports that infants born very preterm (PT), compared with full term (FT), have early differences in rate of learning and motor control that may hinder their ability to learn challenging motor tasks. Four-month-old infants born FT (n = 18) and PT (n = 18) participated in an infant kick-activated mobile task that was scaffolded to motivate progressively higher kicks. We found the FT group learned the association between their leg movements and mobile activation on the second day, but the PT group learned the association on the third day. Both groups of infants increased the height of their kicks on the day they learned the task, compared with their spontaneous kicking height. These findings suggest that infants born PT have the ability to learn challenging motor tasks, such as kicking high, when participating in a task environment that uses scaffolding.