Journal of Applied Biomechanics最新文献

Falls in older adults are a serious public health concern with physical and economic consequences that reduce independence and quality of life. Older adults have morphological changes at the foot and ankle that may disrupt foot neuromechanics and the foot's ability to regulate mechanical leverage and balance during walking. This study quantified age and walking speed effects on mechanical leverage of the foot and ankle, as well as the extent to which interindividual differences in foot-ankle leverage correlated with whole-body balance metrics-the latter during habitual walking and in response to 2 contexts of walking balance perturbations. We found no age effect on peak external moment arms due to ground reaction forces. However, older adults exhibited smaller peak ankle moments, larger ranges of frontal plane whole-body angular momentum, larger anterior-posterior margin of stability, and larger perturbation-induced changes in whole-body angular momentum than younger adults. We also report the first evidence that better foot-ankle leverage during habitual walking correlated with larger margins of stability and smaller ranges of whole-body angular momentum. This study was a first step in understanding the relationship between foot-ankle mechanical leverage and whole-body balance.

During gait analysis, the walking speed of the individual should reflect the walking speed in everyday life. This study compared spatiotemporal and kinematic parameters between 3 conditions of selecting walking speed for treadmill-based gait analysis in healthy adults. We hypothesized that gait parameters collected during self-selected treadmill walking differ from those collected when walking at matched overground speed and self-paced speed. Forty-two healthy participants (40.0 [12.7] y; 16 males) walked on a treadmill in a virtual environment in 3 conditions: speed matching overground speed from the 10-m walk test, self-paced walking, and speed selected by the participant. Spatiotemporal and kinematic parameters were collected using motion capture analysis. Results showed significant differences in walking speed, step length, stride length, step time, stride time, stance time, cadence, peak extension angle of the hip, and peak plantar flexion angle of the ankle between the self-paced condition and matched overground speed (P < .05). These differences in gait parameters were likely due to variations in speed between the 2 conditions. No significant differences were found between treadmill-selected and matched overground speed or self-paced condition. These findings suggest that letting the participant decide their comfortable walking speed is appropriate for speed selection in gait analysis.

Squatting, a closed-kinetic chain exercise, requires the complex coordination of multiple muscles. However, the differences in muscle coordination patterns between individuals with varying levels of exercise proficiency remain unclear. This study aimed to compare muscle coordination patterns during the squat exercise between trained and untrained individuals. Sixteen participants, classified into trained and untrained groups, performed 20 repetitive squats while both motion capture and electromyography data were recorded. Muscle synergy analysis was employed to identify muscle coordination patterns, and cluster analysis was used to determine preferred muscle synergies within each group. The findings indicate that trained individuals exhibit muscle synergies characterized by the coactivation of trunk and leg muscles near the bottom position of the squat. By contrast, untrained individuals primarily show coactivation of leg muscles only. Motion analysis further revealed that trained participants maintained a more upright posture during this phase compared with untrained participants. The distinct muscle synergies between trained and untrained individuals suggest the importance of coordinated trunk and leg muscle activation in maintaining postural control near the bottom position, where the movement transitions from descent to ascent. These insights can inform training strategies to promote effective trunk-leg coordination and postural control in untrained individuals.

To collect reliable data, it is important to determine how inertial measurement unit (IMU) sensor placement affects measurements of segment motion. We aimed to determine the extent to which a functional sensor-to-segment calibration method minimizes the effect of variations in sensor placement on IMU-derived segment angular excursions. Twenty healthy adults walked while wearing 3 IMUs placed on each of the pelvis, thigh, shank, and foot. Differences in estimated segment angular excursions between sensor placements were compared between an assumed sensor-to-segment calibration and 2 versions of a walking-based functional sensor-to-segment calibration. The performance of the functional calibration methods varied. The shank had the greatest difference in root mean square difference between methods (15° for assumed, 1.5° for functional calibration), but the pelvis and thigh did not have significant differences in root mean square difference between assumed and functional calibrations. Mean root mean square differences for angular excursion between sensors were <5° for most comparisons for assumed and functional calibrations. Functional calibration reduced between-subject variance in intersensor differences for all segments. Functional calibration can minimize the effect of variations in IMU sensor placement, but care should be taken to select sensor placements that minimize soft-tissue artifact (eg, anterior thigh).

Marfan syndrome (MFS) is a connective tissue disorder caused by structural changes in fibrillin-1 and is associated with muscle weakness and joint pain. The understanding of lower extremity (LE) joint mechanics associated with joint pain in people with MFS is limited. The goal of this study was to assess LE joint mechanics during the sit-to-stand (STS) task in people with MFS compared with asymptomatic controls. Sixteen people with MFS and 16 sex- and body mass index-matched controls were tested in this study. All participants performed the STS task at a self-selected speed. Peak LE joint extensor moments, moment impulses, moment durations, time to task completion, total support moment (TSM), and each joint's contribution to the TSM were evaluated. People with MFS took longer to perform the task and exhibited lower peak knee extensor moments and higher peak ankle plantar flexor moments compared with controls. Higher LE joint extensor moments impulses and moment durations were observed in people with MFS. People with MFS performed the STS task using a higher TSM with higher ankle contributions to the TSM. People with MFS exhibit altered LE joint mechanics during the STS task and utilize a more ankle joint dominant strategy.

The human foot's unique structure is believed to facilitate our adoption of habitual bipedal locomotion. The foot is particularly important in enabling economical forward propulsion through plantar intrinsic force output and ankle plantar flexor force transfer. An increased capacity for economical forward propulsion would enhance walking performance, that is, faster preferred walking speed (PWS) and improved walking endurance (WE). However, the association between the foot's unique features and walking performance remains unclear. This study investigated whether neuromechanical (flexor digitorum brevis muscle activity and thickness, toe flexor strength) and anthropometric (heel and toe length) foot features associated with PWS and WE (ie, 6-min walk test distance) in younger adults. Stronger toe flexors associated with greater WE (r = .641, P = .010), whereas shorter heels (ie, calcaneus length) associated with faster PWS (r = -.527, P = .044). Stronger toe flexors enhance WE by increasing net propulsion capacity, whereas shorter heels may enable optimal muscle-tendon operating conditions. These insights highlight potential targets for rehabilitation and assistive devices designed to improve walking performance in individuals with gait impairments.

Lower extremities adhering to the spring mechanics proposed by the spring-loaded inverted pendulum (SLIP) model during running are regarded as a form of running-gait optimization among runners. We examined the degree of adherence between experimental and SLIP model-predicted vertical ground reaction force (vGRF) in individuals with unilateral transfemoral amputation. Nine individuals with unilateral transfemoral amputation performed running trials at 6 different speeds on an instrument treadmill. The trials were set at 30% to 80% of their maximum speeds with a 10% increment. The experimental vGRF collected was compared with SLIP model-predicted vGRF. The degree of adherence was calculated using the R2 goodness-of-fit statistics. The experimental vGRF of the affected limbs exhibited a significantly higher degree of adherence than unaffected limbs. There were no significant differences in the degree of adherence between different speed trials for either limb. This finding indicates that running-specific prostheses exhibit mechanical behavior that is consistent with SLIP mechanics, whereas the unaffected limb relies on compensatory, non-SLIP-like strategies. Furthermore, the results suggest that the interaction of running-specific prostheses with other prosthetic components and the residual limb enables the preservation of running mechanics across a range of speeds, thereby supporting the application of SLIP-based modeling to the affected limb.

Instrumented gait analysis has traditionally been isolated to laboratory, marker-based optoelectronic motion capture systems, which limits clinical uptake. Markerless motion capture (MMC) systems driven by trained machine learning algorithms offer high-throughput solutions for translational clinical opportunities. The aim of this study was to examine the day-to-day repeatability of discrete knee kinematic gait metrics in a healthy population using an MMC system uniquely installed in a hospital hallway. Twenty healthy adults (13 females, 7 males) participated in 3 overground hallway gait sessions, on average 11 days apart, using a novel MMC system setup. Intraclass correlation coefficients, standard errors of measurement, and minimal detectable changes were examined for each gait outcome. Results indicated good-to-excellent repeatability, with most (7/8) outcomes having intraclass correlation coefficient values over .86. Standard error of measurement values for all kinematic outcomes were less than 2.0°, and minimal detectable change values were less than 4.7°. Our novel setup of a hospital hallway MMC system produced highly repeatable gait kinematic metrics in a population of healthy adults. Repeatability errors from this study can be used as a healthy reference for future applications of this system.

Lower-extremity exoskeletons (EXOs) may be able to assist with performance and injury risk reduction for military-relevant activities, like walking with loads. However, the effects of EXOs on local dynamic stability (LDS), a measure of motor control, have not been established. Eleven active duty Army Soldiers (9 males, aged 22 [4] y) completed a familiarization session, followed by 2 testing sessions where they did (EXO) or did not (NoEXO) wear a pneumatic powered, knee-actuated EXO. Inertial measurement units were attached bilaterally to the shank and posterior pelvis. Participants completed a 2-mile ruck march on a treadmill at a self-selected pace (1.34 [0.10] m/s), carrying a load equal to 30% of body weight and an additional 9.07 kg for the EXO during that session. LDS was calculated using gyroscope data for 100 strides at the 0.25- (Start) and 2-mile (End) marks of the march. For the right shank, LDS was found to be significantly lower for EXO versus NoEXO (mean difference = 0.28, P < .01, partial η2 = .75). A similar effect was found for the left shank, and while not significant, the effect size was large (P = .07, partial η2 = .29). Finally, LDS was higher at the pelvis in the EXO versus NoEXO, and with a large effect size, although the results were not significant (P = .07, partial η2 = .29). Our results suggest that lower-extremity EXOs reduce distal LDS, which may point to the need for habituation periods for new users of EXOs.