Journal of Applied Biomechanics最新文献

Inverse kinematic alignment (iKA), which preserves the natural knee oblique joint line in total knee arthroplasty, has been shown to produce lower-limb kinematics similar to healthy controls during gait. However, its ability to maintain this advantage during more demanding activities remains unclear. This study evaluated lower-limb kinematics and muscle activation patterns during squatting in individuals who underwent iKA, adjusted mechanical alignment (aMA), and healthy controls. Kinematics were analyzed using a 3D Vicon system, while muscle activation patterns were recorded using electromyography. The iKA group (80.36° [27.43°]) exhibited knee range of motion comparable to healthy controls (95.25° [23.33°]), while the aMA group (67.39° [28.52°]) showed a significant difference (P = .004). Additionally, the aMA group showed reduced hip flexion compared with controls during squatting (P < .001). Although both iKA and aMA groups displayed differences in hip extension and ankle dorsiflexion compared with controls, no differences in muscle activation patterns were observed. These findings suggest that the iKA and aMA groups can squat without altering muscle activity patterns. However, iKA demonstrates biomechanical outcomes that resemble those of healthy controls in certain aspects. Persistent strength deficits in both surgical groups highlight the need for targeted rehabilitation to restore strength.

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.

This study assessed daily and weekly changes in spine mechanical properties, specifically range of motion and passive stiffness, in those with and without sitting-induced low back pain to determine if time-dependent changes in mechanical properties were related to pain development in prolonged sitting. Over 1 week, 20 participants performed their seated office work and attended 5 laboratory sessions (Monday morning and evening, Tuesday morning, Friday evening, and the following Monday morning) to measure lumbar spine stiffness in passive flexion. Accelerometers measured seated lumbar flexion-extension each workday. In the morning and evening, participants provided low back pain ratings and performed maximum voluntary flexion. Statistical tests compared over time and between pain statuses (nonpain < 10 of 100 mm). There were increases in maximum flexion from morning to evening (2.0°; P = .003) and decreases in angular breakpoints on Monday evening and Tuesday morning (4.6% and 6.8% of passive flexion; P ≥ .056). Classification of seated spine flexion-extension into the transition and high stiffness zones of the passive curve (ie, moderate-high flexion) revealed that sitting strained the posterior passive tissues, likely contributing to the changes in range of motion and stiffness. Nevertheless, alterations in spine properties did not accumulate throughout the week and were not different by pain status.

Foot strength is important for gait, balance, and function, but it is challenging to measure. Evidence explaining why strength differences exist between sitting and standing test positions is needed to improve clinical value. Observing changes in ground reaction force (Δ GRF) during strength testing may help explain these differences. Our purpose was to determine if Δ GRF differed between test positions, and if Δ GRF was associated with strength. Twenty healthy adults (x¯ = 24.7 y) were randomly assigned to a first test position, sitting or standing. With one foot on a force plate, subjects pressed down and pulled with their toes on a towel connected to a scale, for each test position. Paired t tests and Pearson correlation coefficients were used in analyses of strength and 3D Δ GRF outcomes. Mean peak foot strength and Δ GRFx (anterior-posterior direction) were greater in standing (P < .001). Correlations were strong between sitting and standing peak strength (r = .703) and between peak strength and Δ GRFx (r = .738) and Δ GRFz (superior-inferior) (r = .595) in standing. Greater strength production in standing, which was directly correlated to Δ GRF, was congruent with task demands and may reflect the importance of rearfoot stability during foot strength testing. From a clinical perspective, the standing test position is favored over sitting.

This study applied decision-tree (DT) machine learning models to determine whether this approach is more accurate when classifying slip outcome during walking, and to refine the cutoff thresholds of each slip type. Kinematic data of the heel were collected from 50 adults (23.1 [3.6] y) during 516 walking trials. The first DT model (DT1) was trained with heel slip distance and heel slip velocity as predictor variables; the second model (DT2) added heel slip acceleration as the third predictor variable. Walking trials were first classified as a no-slip, slip-recovery, or slip-fall outcome based on visual observation, and these classifications were used as response labels to train the DT models. Results indicated that both DT models yielded different thresholds in classifying slip outcomes and were similar to thresholds suggested in previous studies. However, both DT models resulted in 4.1% to 7.6% greater overall prediction accuracy compared with previously suggested thresholds, with DT2 generally performing better than DT1. Although the improved performance was offset by a ∼7% lower sensitivity when classifying no-slip outcomes and greater model complexity, future studies examining slip responses during gait should incorporate the thresholds derived from the DT2 model to most accurately classify the type of slip outcome.

Gait symmetry is often assumed in healthy individuals, yet functional asymmetries arise from biomechanical and neurophysiological factors. Although light upper body loading can improve walking performance, its effect on lower limb joint asymmetry remains unclear. This study examined how different loading conditions affect sagittal plane gait asymmetry at the hip, knee, and ankle. Twenty-two participants walked under 4 conditions: no weight, unilateral arm weight, bilateral arm weights, and waist weights each using 0.45-kg loads. Three-dimensional joint angles were normalized to 101 points across the gait cycle. Asymmetry was assessed using statistical parametric mapping and pointwise effect size. Two metrics were used: (1) temporal extent, defined as the percentage of the gait cycle with significant left-right differences (P < .05) and the percentage of the gait cycle with effect size >0.8 and (2) group-level prevalence, defined as the percentage of participants showing significant asymmetry at each time point. Significant asymmetries were observed across all joints and conditions, with hip and knee levels consistently exceeding those at the ankle. Effect size values often exceeded statistical thresholds, highlighting meaningful differences. Loading produced minimal systematic effects, though individual responses varied. Importantly, light arm weights did not increase asymmetry, supporting their use for gait enhancement.

Clarification of glenohumeral joint alignment changes during the late cocking phase may reveal the mechanisms of throwing injuries. This study aimed to determine the effect of shoulder external rotation on humeral head center deviation relative to the scapular glenoid. Twenty-eight baseball players participated. The anteroposterior deviation of the humeral head center relative to the glenoid (humeral head translation) and the distance between the humeral head and posterior glenoid rim perpendicular to the glenoid articular surface (posterior glenohumeral distance) were measured. Magnetic resonance imaging of the throwing shoulder was performed at 90° abduction with 90°, 100°, and 110° external rotation; for the nonthrowing shoulder, measurements were conducted at 90° and 100°. In humeral head translation, the posterior translation of the humeral head relative to the glenoid was significantly greater at 110° compared to 90° external rotation position (P = .003). Humeral head translation was associated with posterior glenohumeral distance at the 90° (β-coefficient = 0.649) and 100° (β-coefficient = 0.556) external rotation positions. Increased shoulder external rotation resulted in posterior translation of the humeral head and proximity between the humeral head and the posterior glenoid rim. The factors identified as contributing to posterior deviation of the humeral head may trigger throwing shoulder injuries during the late cocking phase.

Delayed-onset muscle soreness (DOMS) is a noninvasive pain model offering a unique opportunity to study trunk neuromuscular adaptations. While prior research has examined regional muscle activation in the lumbar region, the spatial distribution of median frequencies (MF) under DOMS has not been explored. This study investigated the effect of DOMS-induced pain on the spatial distribution of MF in the lumbar erector spinae muscles and its association with trunk force variability during submaximal contractions. Twenty healthy adults completed 2 laboratory sessions: 1 pain-free and 1 under low back DOMS. High-density surface electromyography was recorded bilaterally on the erector spinae during submaximal isometric trunk extensions. MF distribution was analyzed using centroid coordinates with and without DOMS. Force variability was also assessed. DOMS significantly increased perceived muscle pain and soreness in the lumbar region. It also caused a cranial and medial shift of the MF centroid, significant on 1 side of the trunk. However, force variability remained stable between conditions. These results suggest that DOMS induces regional adaptations in lumbar muscle MF. The spatial distribution of MF may serve as a novel and sensitive marker of neuromuscular adaptation to pain. The trunk system was able to maintain force steadiness despite pain and soreness.