BACKGROUND: Barefoot runners have a higher probability of lower leg and foot disorders compared to runners wearing traditional running shoes. However, the site of muscle stress due to barefoot running has not been reported. This study aimed to investigate the effects of shod and barefoot running on muscle mechanical properties. METHODS: Atotal of 18 healthy male subjects were included in this study and were assigned to either the shod running group or the barefoot running group. While the shod group ran on the treadmill at a speed of 75% heart rate reserve for 45 min with shoes, the barefoot group ran without shoes after warm-up session. As an index of muscle stiffness, the shear wave velocity (SWV) of the eleven lower extremity muscles were measured at rest before and after exercise using shear wave elastography. RESULTS: The tibialis posterior SWV was increased after running in the shod (3.67±0.41 m/s to 3.90±0.45 m/s) and barefoot (3.70±0.36 m/s to 4.02±0.54 m/s) groups. In contrast, the vastus lateralis SWV was increased only in the shod group (2.62±0.32 m/s to 2.80±0.34 m/s), while the peroneus muscle SWV increased only in the barefoot group (3.24±0.48 m/s to 3.50±0.55 m/s and 2.92±0.5 m/s to 3.11±0.49 m/s for the superficial and deep layers, respectively). CONCLUSIONS: The shod condition selectively influences changes in the stiffness of the vastus lateralis and peroneus muscles during running but has no effect on the tibialis posterior.

<title>Abstract</title><sec>
<title>Background</title>
Early childhood is a transferring stage between the two accelerated growth periods (infant and adolescent). Body dimensions are related to physical growth and development. The purpose of this study was to investigate physical growth in terms of anthropometry, muscle growth of the lower extremity, and functional development over early childhood.


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<title>Methods</title>
A cross-sectional study was carried out on 29 preschool children (PS: 3–5 years), 21 school children (SC: 6–8 years), and 22 adults (AD: 20–35 years). Lower extremity characteristics (segmental dimensions, muscle and adipose tissue thicknesses of the thigh and lower leg), and voluntary joint torque (knee and ankle) were measured. Correlations between parameters and group comparisons were performed.


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<title>Results</title>
All the parameters except for body mass index (BMI) and subcutaneous adipose tissue thickness were correlated with age for PS and SC combined (<italic>r</italic> = 0.479–0.920, <italic>p</italic> &lt; 0.01). Relative thigh and shank lengths to body height were greatest in AD and smallest in PS (<italic>p</italic> &lt; 0.05) but the relative foot dimensions were significantly larger in PS and SC than in AD (<italic>p</italic> &lt; 0.05). Relative subcutaneous adipose tissue thickness was largest in PS and lowest in AD. Muscle thickness and the muscle volume measure (estimated from muscle thickness and limb length) were significantly larger in older age groups (<italic>p</italic> &lt; 0.05). All groups showed comparable muscle thickness when normalized to limb length. Joint torque normalized to estimated muscle volume was greatest for AD, followed by SC and PS (<italic>p</italic> &lt; 0.05).


</sec><sec>
<title>Conclusions</title>
Relative lower extremity lengths increase with age, except for the foot dimensions. Muscle size increases with age in proportion to the limb length, while relative adiposity decreases. Torque-producing capacity is highly variable in children and rapidly develops toward adulthood. This cross-sectional study suggests that children are not a small scale version of adults, neither morphologically nor functionally.


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<title>Abstract</title>Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; however, track distance running in a counterclockwise direction exposes the runner’s feet to asymmetrical stress. This may induce asymmetrical adaptation in the runners’ foot arch functions, but this has not been experimentally tested. Here, we show that the plantar fascia (PF), a primary structure of the foot arch elasticity, is stiffer for the left than the right foot as a characteristic of runners, via a cross-sectional study on 10 track distance runners and 10 untrained individuals. Shear wave velocity (index of tissue stiffness: SWV) and thickness of PF and foot dimensions were compared between sides and groups. Runners showed higher PF SWV in their left (9.4 ± 1.0 m/s) than right (8.9 ± 0.9 m/s) feet, whereas untrained individuals showed no bilateral differences (8.5 ± 1.5 m/s and 8.6 ± 1.7 m/s, respectively). Additionally, runners showed higher left to right (L/R) ratio of PF SWV than untrained men (105.1% and 97.7%, respectively). PF thickness and foot dimensions were not significantly different between sides or groups. These results demonstrate stiffer PF in the left feet of runners, which may reflect adaptation to their running-specific training that involves asymmetrical mechanical loading.

Joint angle dependence and site specificity of the plantar fascial dimensions and SWV were examined by combining sagittal magnetic resonance and supersonic shear imaging techniques. We revealed that the site-specific changes in PF SWV were related to joint angle positions, i.e., PF slackness and elasticity changed in varying combinations of ankle and MTP angle. Our findings suggest that PF can elastically support the foot arch throughout the stance phase of human bipedal locomotion.

BACKGROUNDS: Joint kinetic calculations are sensitive to joint centre locations. Although geometric hip and knee joint centre/axis are generally developed, the ankle joint centre (AJC) is conventionally defined as the midpoint between the malleolus lateralis and medialis (AJCMID) in most gait analyses. RESEARCH QUESTION: We examined the positional difference of the AJCMID from the geometric centre of rotation (AJCFUN) and its effect on the ankle joint kinetics in representative human gaits. METHODS: In the first experiment, we calculated the AJCFUN and indicated its location on the ankle MRI in 14 (seven male and seven female) participants. In the second experiment, we compared ankle kinematics/kinetics based on AJCFUN and AJCMID during walking and hopping at 2.6 Hz in 17 (nine male and eight female) participants. RESULTS: In both experiments, AJCFUN was located at positions significantly medial (-9.2 ± 5.4 mm and -10.1 ± 4.4 mm) and anterior (17.0 ± 7.4 mm and 15.3 ± 5.2 mm) from the AJCMID. Furthermore, the AJCMID underestimated peak dorsiflexion (AJCMID/AJCFUN: 52.6 ± 17.1%) and inversion (AJCMID/AJCFUN: 62.2 ± 11.5%) torques and their durations in walking. Additionally, AJCMID overestimated the plantar flexion torque in both gait modes [AJCMID/AJCFUN: 111.3 ± 4.8% (walking) and 112.7 ± 6.3% (hopping)]. SIGNIFICANCE: We therefore concluded that the positional difference between the geometric and landmark-based AJC definitions significantly affected ankle kinetics, thereby indicating that the functional method should be used for defining AJC for gait analysis.

Long-distance running (LDR) can induce transient lowering of the foot arch, which may be associated with mechanical fatigue of the plantar fascia (PF). However, this has not been experimentally tested in vivo. The purpose of this study was to test our hypothesis that LDR induces transient and site-specific changes in PF stiffness and morphology and that those changes are related to the lowering of the foot arch. Ten male recreational long-distance runners and 10 untrained men were requested to run overground for 10 km. Before and after running, shear wave velocity (SWV: an index of soft tissue stiffness) and thickness of PF at three different sites from its proximal to distal end were measured using supersonic shear imaging and B-mode ultrasonography. Foot dimensions including the navicular height were measured using a three-dimensional foot scanner. SWV at the proximal site of PF and navicular height was significantly decreased in both groups after running, with a higher degree in untrained men (−21.9% and −14.1%, respectively) than in runners (−4.0% and −6.3%, respectively). The relative change (%Δ) in SWV was positively correlated with %Δnavicular height in both groups (r =.69 and r =.65, respectively). Multiple regression analysis revealed that %ΔSWV at the proximal site solely explained 72.7% of the total variance in %Δnavicular height. It is concluded that LDR induces transient and site-specific decreases in PF stiffness. These results suggest that the majority of running-induced lowering of the foot arch is attributable to the reduction of PF stiffness at the proximal site.

The purpose of this study was to investigate the site- and sex-differences in the morphological and mechanical properties of the plantar fascia (PF) in humans. The thickness and shear wave velocity (SWV) of PF at five different sites between the medial calcaneal tubercle and the second toe were measured for 40 healthy young participants (20 males and 20 females) using supersonic shear imaging (SSI). The thickness and SWV measurements were highly repeatable (ICC ≥ 0.93). The proximal sites of PF around the calcaneal attachment were significantly thicker and stiffer (higher SWV values) than the middle and distal sites (p < 0.05). In addition, females had significantly thinner PF in proximal and middle sites than males, while being significantly stiffer in regardless of the sites, compared with males (p < 0.05). The results of the present study partly support previous findings on the site- and sex-differences in PF morphology, and further reveal inhomogeneity and sex-specificity of PF stiffness. The present study widely opens the possibility of evaluating PF functions in vivo.