During walking, uninjured individuals maintain whole-body angular momentum (WBAM) within a narrow range. Individuals with lower limb amputation (LLA) have demonstrated larger WBAM ranges during walking relative to uninjured controls, suggesting disrupted WBAM control. Given that the trunk is a principal contributor to WBAM and trunk control may be altered after LLA, we related trunk postural control isolated during unstable sitting and WBAM control during walking across 9 individuals with unilateral transfemoral amputation, 24 individuals with unilateral transtibial amputation, and 16 uninjured controls. Linear regressions revealed weak relationships (R2 = .050-.350, P < .071), particularly in the sagittal and transverse planes, between trunk postural control measures and WBAM ranges. Trunk postural control measures during unstable sitting were larger among individuals with LLA versus uninjured controls (P < .029) but were not different between individuals with transtibial amputation versus transfemoral amputation. Similarly, WBAM ranges during walking were larger in all planes between individuals with LLA versus uninjured controls (P < .005), with individuals with transtibial amputation having larger ranges than individuals with transfemoral amputation in the sagittal (P < .001) and frontal (P = .006) but not the transverse (P = 1.000) planes. Our findings suggest that trunk postural control during unstable sitting does not explain differences in WBAM control during walking among individuals with versus without LLA, particularly in the sagittal and transverse planes.

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).

Cross-country runners' risk for injury is high in-season potentially due to changes in biomechanics during prescribed fast running speeds and competitions. The purpose of this study was to determine if biomechanics associated with overuse knee and lower leg injury during running change similarly across speeds between female and male collegiate cross-country runners. Sixteen collegiate cross-country runners (8 females) participated. A self-selected running speed was entered into regression equations to determine treadmill speeds for the conditions: recovery (∼9% slower), threshold (∼25% faster), interval (∼36% faster), and repetition (∼50% faster). Three-dimensional lower-extremity biomechanics were collected during running. Dependent variables were analyzed via mixed-model analysis of variance and pairwise post hoc tests. Both peak rearfoot angle increased (P = .005, Cohen's f = 0.84)and rearfoot excursion increased (P = .002, Cohen's f = 0.88) with the conditions' treadmill speed. Peak knee adduction angle was greater in females compared with males (P = .032, Cohen's f = 0.67) during: recovery, easy, threshold, and interval conditions. Increases in running speed affected joint kinematics and kinetics similarly between groups. Generally, similar running biomechanics observed between females and males may indicate that faster training speeds could accentuate the contribution of rearfoot eversion to lower leg overuse injury.

Proximal control and lower extremity (LE) movement related to foot function may be an important factor for plantar fasciitis (PF) during running. This study aimed to investigate hip muscle activity and frontal plane LE kinematics during running between long-distance runners with and without PF. The electromyographic amplitude of the hip muscles (tensor fascia latae, gluteus medius, gluteus maximus) and frontal plane LE joint angles (ankle, knee, and hip range of motion during stance phase) of 30 habitually shod long-distance runners (15 with acute PF and 15 healthy controls) were simultaneously recorded using surface electromyography, 8 infrared cameras, and force plates while they ran barefoot at a speed of 3 to 3.67m·s-1. Independent t test and 2-way analysis of variance were used to analyze the differences for dependent variables. The PF group had significantly lower tensor fascia latae (P = .040, effect size = 0.259) and gluteus medius (P = .014, effect size = 0.197) activation during the swing phase and gluteus maximus (P = .012, effect size = 0.207) activation during the stance phase compared with the control group. Moreover, the PF group showed significantly greater joint angular excursions of the contralateral pelvic drop (P = .049, effect size = 0.75), hip adduction (P = .019, effect size = 0.91), knee abduction (P = .040, effect size = 0.79), and rearfoot eversion (P = .004, effect size = 1.14) during the stance phase than the control group. Adding assessment of hip muscle activity and LE joint angles during running would be beneficial for evaluating runners with PF.

The calf raise test (CRT) is commonly used to assess triceps surae muscle-tendon unit function. Often, a metronome set to 60beats/min (30 repetitions/min) is used to set the cadence of calf raise repetitions, but studies report using cadences ranging from 30 to 120beats/min. We investigated the effect of cadence on CRT outcomes, accounting for the potential confounders of sex, age, body mass index, and physical activity. Thirty-six healthy individuals (50% female) performed single-leg calf raise repetitions to volitional exhaustion in 3 randomized cadence conditions, 7 days apart: 30, 60, and 120beats/min. Repetitions, total vertical displacement, total work, peak height, and peak power were recorded using the validated Calf Raise application. Cadence significantly affected all CRT outcomes (P ≤ .008), except repetitions (P = .200). Post hoc analysis revealed 60beats/min resulted in significantly greater total vertical displacement and work than 30 and 120beats/min. Peak height was greater at 60 and 120 than 30beats/min, and peak power was greater at 120beats/min. Males generated greater work and peak power (P ≤ .001), whereas individuals with greater body mass index completed less repetitions (P = .008), achieved lower total vertical displacements (P = .003), and generated greater peak power (P = .005). CRT cadence is important to consider when interpreting CRT outcomes and comparing data between studies.

Performance of ballistic movements to drive a ball toward a spatial target in different sports requires high movement speed associated with spatial accuracy. In this investigation, we compared target hitting movements performed from very low to very high movement speeds with the purpose of assessing the effects on movement accuracy and variability. Participants were 16 young men, naive for the experimental task. The task consisted of sliding a handle over a flat surface to hit a moveable disc, with the aim of driving it toward a spatial target. Kinematic analysis indicated that the high and very high movement speeds induced the lowest peak and contact velocity variabilities of the handle displacement and elbow extension. Assessment of interjoint coordination between the shoulder, elbow, and wrist indicated higher relative phase values in very high speed compared with lower movement speeds. As the main outcome, we found no evidence for effects on either spatial accuracy or variability of the disk displacement toward the target due to increment of movement speed. Our findings support the conclusion that ballistic skills can be performed with high movement speeds while keeping spatial accuracy and variability unchanged.

Hip joint center (HJC) location estimation influences dependent angles and clinical interpretations. We examined the agreement between 6 HJC estimation methods; compared hip, thigh, and knee angles; and explored HJC location and thigh angle associations. Pelvis markers were used to estimate HJC location via 6 popular methods using Harrington's method as the reference standard. HJC limits of agreement analysis and inferential angle comparisons during standing revealed that Bell's (HJC bias range = 0-11mm, hip angle difference range = -0.2° to 0.1°) and Vaughan's (HJC bias range = -5 to 41mm, hip angle difference range = -0.5° to -5.3°) methods were most and least like Harrington's but varied by dimension. Stepwise regression showed that anterior-posterior, medial-lateral, and anterior-posterior HJC coordinate differences best explained sagittal (R2 range = .95-.99, P < .001), frontal (R2 range = .83-.99, P < .001), and transverse (R2 range = .54-.72, P < .001) thigh angle differences, respectively. Different HJC methods caused several large sagittal but more minor frontal and transverse plane differences. We urge caution when using different HJC methods.

Previous studies on sprinting biomechanics have identified a variety of biomechanical characteristics that describe the outcome of improved sprint technique but in doing so have neglected to identify the postural control strategies that lead to improved sprint performance. The purpose of this study was to evaluate the relationship between frontal plane displacement of the center of mass (CoM) and sprint velocity, and to understand if multijoint coordination of the limbs and trunk were associated with minimizing the displacement. The results from this study suggest that stance phase frontal plane CoM cumulative path length is significantly associated with sprint velocity. Further, a multivariate linear regression model revealed that coordinative couplings of the bilateral limbs and trunk were associated with the minimization of the frontal plane CoM displacement. Specifically, the coordination of the knees (flexion-extension) and axial rotation of the thorax-pelvis were the most important interjoint couplings in minimizing frontal plane CoM displacement. Frontal plane CoM displacement provides coaches, athletes, and performance professionals with an interpretable metric to identify sprint technique quality in field using wearable sensors. Future work needs to further advance our understanding of postural control during sprinting so that effective coaching and rehabilitation interventions can be designed.