Walking with head-mounted virtual and augmented reality devices : effects on position control and gait biomechanics

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 (p0.082), 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

Biomechanical outcomes due to impact loading in runners while looking sideways

A stable gaze is necessary to optimize visual conditions during running. Head accelerations generally remain stable when looking in front; however, it is unclear if this response is similar when the head is turned sideways, and whether other adaptive strategies are present to maintain this stability. The purpose of this study, therefore, was to examine whether runners maintained stable head accelerations while gazing at fixed targets in front and to their sides. The authors collected biomechanical data from 13 runners as they directed their gaze to visual targets located in front, 45°, and 90° to the sides at a random sequence. Vertical head and tibial accelerations were the primary outcome measures, while vertical loading rate, footstrike angle, contact time, stride length, and stride rate were the secondary measures. A reduction in vertical head accelerations was found in the rightmost direction (P=.04), while an increase in vertical tibial accelerations was found on the same direction (P=.02). No other significant differences were observed for the other variables. The results of this study suggest that the tibia accommodated the increased shock to maintain head stability

Control of impact loading during distracted running before and after gait retraining in runners

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 0.68). Visual feedback after gait retraining reduced PPA and vertical loading rates during distracted running (P 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

Shoe-mounted accelerometers should be used with caution in gait retraining

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 0.098) 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

Shoe‐mounted accelerometers should be used with caution in gait retraining

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 0.098) 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

Does vertical head shock remain stable during running while looking sideways?

Rationale/Objectives: The head is stabilized during running for navigation by modulations of lower limb shock. However, past studies had only tested the head stability when subjects were gazing forward. The modulation of vertical head shock (VHS) when looking sideways during running however remains unclear. The present study investigated whether VHS would remain stable when runners gazing at fixed-distance targets from multiple directions at eye level. Methods: Thirteen right-handed runners were asked to run on a self-paced treadmill with standard test shoes. Peak VHS and vertical tibial shock (VTS) were measured by two wireless accelerometers attached separately to the forehand and right distal tibia. Five small boxes with RGB LED lights were positioned two meters away from the center of the treadmill in front (i.e. at 0°), ±45° and ±90°. Each LED light was flashed once for 30 seconds during the running trial in a randomized sequence. Subjects were instructed to turn their gaze towards the flashing LED light and to keep their gaze at the light until the light was turned off. We compared peak VHS and VTS between gazing directions using repeated measures ANOVA. Results: We found stable VHS in general except that peak VHS was slightly smaller when runners were looking at the rightmost direction (p=0.04, Cohen’s d=0.100) and VTS was higher in the same rightmost direction (p=0.016, Cohen’s d=0.146). Conclusions: Head generally remains stable during running, except when gazing to an object 90° to the right. At such extreme gazing direction, we also observed changes in the lower limb kinetics for compensating the changes in VHS

Effects of coach-based gait retraining program on running biomechanics in runners

Rationale/Objectives: Laboratory-based gait retraining has been reported to successfully reduce impact loading in runners. Pose® Method of running is a popular coach-based gait retraining program aimed to modify running posture and prevent running injury. However, little is known about the effects of this program on running biomechanics. Hence, we sought to examine the running biomechanics in runners before and after a course of Pose® Method gait retraining. Methods: Fourteen recreational runners underwent a 4-week coach-based gait retraining program (2 sessions per week, and each session lasted 1.5 hours) delivered by a certified Pose® Method coach. We collected running kinematics and kinetics from 10 self-paced overground running trials before and after the training using motion capture system and force plate. Pre- and post-training vertical average (VALR) and instantaneous loading rates (VILR), lower limb kinematics, and foot strike angle (FSA) were compared using paired t-tests. Results: Participants exhibited no significant difference in both VALR (p=0.693) and VILR (p=0.782) after training. However, we found significantly greater hip flexion (Cohen’s d=0.84, p=0.008) and knee flexion (Cohen’s d=1.1, p=0.003) during swing phase. Besides, runners exhibited a significant reduction in the FSA after training (Cohen’s d=0.83, p=0.008), indicating a switch of footstrike pattern from heelstrike to midfoot strike landing. Conclusions: This study demonstrated a footstrike pattern switch and some kinematics changes at the hip and knee joint during swing phase after a course of Pose® Method gait retraining in runners. However, vertical loading rates, which are injury-related biomechanical markers, remained similar

[In Press] Running biomechanics before and after Pose® method gait retraining in distance runners

Pose® Method gait retraining has been claimed to modify running form and prevent injury. This study examined the running biomechanics before and after Pose® Method gait retraining. Fourteen runners underwent a 4-week Pose® Method gait retraining program delivered by a certified coach. Paired t-tests were employed to compare vertical average (VALR) and instantaneous loading rates (VILR), lower limb kinematics, footstrike angle and trunk flexion in the sagittal plane before and after the training. Kinetically, there were no significant differences in the VALR (p= 0.693) and VILR (p= 0.782) before and after the training. Kinematically, participants exhibited greater peak hip flexion (p= 0.008) and knee flexion (p= 0.003) during swing. Footstrike angle also reduced significantly (p= 0.008), indicating a footstrike pattern switch from rearfoot strike to midfoot strike. There was no significant difference in the trunk flexion in the sagittal plane after training (p= 0.658). After a course of Pose® Method gait retraining, runners demonstrated a footstrike pattern switch and some kinematics changes at the hip and knee joint during swing. However, injury related biomechanical markers (e.g., VALR and VILR) and the trunk kinematics remained similar after training. Runners may consider other gait retraining programs for impact loading reduction

Type effect of inhibitory KT tape on measured vs. perceived maximal grip strength

This study examined the effects of KT tape (KT) applied in an inhibitory manner on muscle activity, measured maximal grip strength, and perceived maximal grip strength in regular KT-users and nonusers. This study was a single-blinded crossover study with sixty participants including 27 kT-users and 33 non-users. Participants underwent maximal grip strength tests with and without inhibitory KT applied across the wrist extensors. Muscle activity and maximal grip strength were measured, while perceived maximal grip strength was rated using a visual analogue scale. No significant interaction effect was found between taping conditions and participant KT-experience for muscle activity (F = 0.825, p = 0.367), measured grip strength (F = 1.018, p = 0.317) or perceived grip strength (F = 0.122, p = 0.728). No significant differences were observed in the EMG activity between taping conditions for either KTusers (p = 0.367) or non-users (p = 0.215). A similar trend was found in the measured grip strength (KT-users: p = 0.317; non-users: p = 0.294) and perceived grip strength (KT-users: p = 0.728; non-users: p = 0.063). KT applied in an inhibitory manner does not impede EMG activity, measured maximal grip strength, or perceived maximal grip strength in adults, regardless of their preconceived notions of KT