18Background: With distance running gaining popularity, there is a concurrent increase in

Complex motor commands for human locomotion are generated through the combination of motor modules representable as muscle synergies. Recent data have argued that muscle synergies are inborn or determined early in life, but development of the neuromusculoskeletal system and acquisition of new skills may demand fine-tuning or reshaping of the early synergies. We seek to understand how locomotor synergies change during development and training by studying the synergies for running in preschoolers and diverse adults from sedentary subjects to elite marathoners, totaling 63 subjects assessed over 100 sessions. During development, synergies are fractionated into units with fewer muscles. As adults train to run, specific synergies coalesce to become merged synergies. Presences of specific synergy-merging patterns correlate with enhanced or reduced running efficiency. Fractionation and merging of muscle synergies may be a mechanism for modifying early motor modules (Nature) to accommodate the changing limb biomechanics and influences from sensorimotor training (Nurture).

Real‐time biofeedback gait retraining has been reported to be an effective intervention to lower the impact loading during gait. While many of the previous gait retraining studies have utilized a laboratory‐based setup, some studies used accelerometers affixed at the distal tibia to allow training outside the laboratory environment. However, many commercial sensors for gait modification are shoe‐mounted. Hence, this study sought to compare impact loading parameters measured by shoe‐mounted and tibia sensors in participants before and after a course of walking or running retraining using signal source from the shoe‐mounted sensors. We also compared the correlations between peak positive acceleration measured at shoe (PPAS) and tibia (PPAT) and vertical loading rates, as these loading rates have been related to injury. Twenty‐four and 14 participants underwent a 2‐week visual biofeedback walking and running retraining, respectively. Participants in the walking retraining group experienced lower PPAS following the intervention (P < 0.005). However, they demonstrated no change in PPAT (P = 0.409) nor vertical loading rates (P > 0.098) following the walking retraining. In contrast, participants in the running retraining group experienced a reduction in the PPAT (P = 0.001) and vertical loading rates (P < 0.013) after running retraining. PPAS values were four times that of PPAT for both walking and running suggesting an uncoupling of the shoe with tibia. As such, PPAS was not correlated with vertical loading rates for either walking or running, while significant correlations between PPAT and vertical loading rates were noted. The present study suggests potential limitations of the existing commercial shoe‐mounted sensors.

Gait retraining using visual biofeedback has been reported to reduce impact loading in runners. However, most of the previous studies did not adequately examine the level of motor learning after training, as the modified gait pattern was not tested in a dual-task condition. Hence, this study sought to compare the landing peak positive acceleration (PPA) and vertical loading rates during distracted running before and after gait retraining. Sixteen recreational runners underwent a two-week visual biofeedback gait retraining program for impact loading reduction, with feedback on the PPA measured at heel. In the evaluation of PPA and vertical loading rates before and after the retraining, the participants performed a cognitive and verbal counting task while running. Repeated measures ANOVA indicated a significant interaction between feedback and training on PPA (F = 4.642; P = 0.048) but not vertical loading rates (F > 1.953; P > 0.067). Pairwise comparisons indicated a significantly lower PPA and vertical loading rates after gait retraining (P < 0.007; Cohen's d > 0.68). Visual feedback after gait retraining reduced PPA and vertical loading rates during distracted running (P < 0.033; Cohen's d > 0.36). Gait retraining is effective in lowering impact loading even when the runners are distracted. In dual-task situation, visual biofeedback provided beneficial influence on kinetics control after gait retraining.

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A new model of running shoes which features an extreme cushioning and an oversized midsole, known as the maximalist (MAX) was launched. This design claims to provide excellent shock absorption, particularly during downhill running. This study sought to assess the effects of MAX on the external impact loading, footstrike pattern, and stride length during level ground and downhill running on an instrumented treadmill. Twenty-seven distance runners completed four 5-minute running trials in the two footwear conditions (MAX and traditional running shoes (TRS)) on a level surface (0%) and downhill (10%-declination). Average and instantaneous loading rates (ILRs), footstrike pattern and stride length were measured during the last minute of each running trial. A 12% greater ILR was observed in downhill running with MAX (p = .045; Cohen's d = 0.44) as compared to TRS. No significant difference was found in the loading rates (p > .589) and stride length (p = .924) when running on a level surface. Majority of runners maintained the same footstrike pattern in both footwear conditions. Findings of this study suggested that MAX might not reduce the external impact loading in runners during level and downhill treadmill running. Instead, this type of footwear may conceivably increase the external impact loading during downhill treadmill running.

What was once a science fiction fantasy, virtual reality (VR) technology has evolved and come a long way. Together with augmented reality (AR) technology, these simulations of an alternative environment have been incorporated into rehabilitation treatments. The introduction of head-mounted displays has made VR/AR devices more intuitive and compact, and no longer limited to upper-limb rehabilitation. However, there is still limited evidence supporting the use of VR and AR technology during locomotion, especially regarding the safety and efficacy relating to walking biomechanics. Therefore, the objective of this study is to explore the limitations of such technology through gait analysis. In this study, thirteen participants walked on a treadmill in normal, virtual and augmented versions of the laboratory environment. A series of spatiotemporal parameters and lower-limb joint angles were compared between conditions. The center of pressure (CoP) ellipse area (95% confidence ellipse) was significantly different between conditions (p = 0.002). Pairwise comparisons indicated a significantly greater CoP ellipse area for both the AR (p = 0.002) and VR (p = 0.005) conditions when compared to the normal laboratory condition. Furthermore, there was a significant difference in stride length (p<0.001) and cadence (p<0.001) between conditions. No statistically significant difference was found in the hip, knee and ankle joint kinematics between the three conditions (p>0.082), except for maximum ankle plantarflexion (p = 0.001). These differences in CoP ellipse area indicate that users of head-mounted VR/AR devices had difficulty maintaining a stable position on the treadmill. Also, differences in the gait parameters suggest that users walked with an unusual gait pattern which could potentially affect the effectiveness of gait rehabilitation treatments. Based on these results, position guidance in the form of feedback and the use of specialized treadmills should be considered when using head-mounted VR/AR devices.