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The objective of this study was to examine the influence of relative hamstring flexibility and lumbar extensor strength on lumbar flexion during a stoop lift. Lumbar flexion during stoop lifting has been associated with increased bending stress and load on the lumbar spine. The potential impairments that contribute to a flexed lumbar lifting posture during stoop lifting are unclear. Forty-nine healthy individuals (27 females and 22 males) between the ages of 18 and 40 participated. Strength of the lumbar extensors was measured with a motor-driven dynamometer, and relative hamstring flexibility was estimated with the passive knee extension test. Peak lumbar flexion and pelvis anterior rotation were quantified with 3D motion capture during a stoop lift. There was a positive correlation between relative hamstring flexibility and peak pelvis anterior rotation angle during the stoop lift (r = .544, P < .001). Meanwhile, there was a negative correlation between middle lumbar spine peak flexion and relative hamstring flexibility (r = −.538, P < .001) and a negative correlation between lumbar extensor strength and lower lumbar peak flexion (r = −.288, P = .045). Individuals with decreased strength and limited relative hamstring flexibility tended to exhibit increased lumbar flexion during stoop lifting.

A higher risk of knee osteoarthritis (OA) has been identified in patients with slower walking speeds following anterior cruciate ligament reconstruction (ACLR). Given that altered loading of the surgical knee has been the most proposed mechanism for early knee OA post-ACLR, understanding how modulating walking speed may modify knee joint loading is essential for developing strategies to reduce the risk of knee OA in ACLR patients. The purpose of this study was to determine how modulation of walking speed affects knee joint loading during overground walking post-ACLR. Lower extremity kinematics and kinetics were recorded during overground walking at a self-selected, slower, and faster speed from 16 patients with unilateral ACLR. The results showed that ACLR patients demonstrated lesser peak knee flexion and adduction moments of the surgical knees when walking at slower speeds. However, modulating walking speed did not alter between-limb knee loading asymmetry. The ACLR limbs had lower peak knee flexion moments than the uninjured limbs across all 3 walking speeds. Although interventions that increase walking speed may deter the onset of knee OA by elevating the mechanical stimulation at the surgical knee, additional gait training strategies may be needed to restore the between-limb loading symmetry in ACLR patients.

The effect of gait speed on minimum toe clearance (MTC) amount may vary across the lifespan due to changes in joint relationships, potentially affecting trip-related fall risk in older adults. We evaluated whether age influences the relationship between gait speed and MTC amount, as well as between joint movements and MTC amount. Optical motion capture data was collected on 62 participants between the ages of 20 and 83 years during 25 gait trials at self-selected normal, fast, and slow speeds. Multilevel models were used for data analysis. Gait speed was associated with a 0.13 cm increase in MTC amount for every meter per second increase in gait speed with other factors constant and was unaffected by age. Ankle dorsi–plantarflexion, knee and hip flexion–extension, and stance hip abduction–adduction changed the MTC amount by 0.05, 0.02, 0.04, and 0.04 cm, respectively, for each degree of joint movement, with other factors constant, and was unaffected by age. Age did not affect the relationship between gait speed and MTC amount, nor the relationship of joint moments with MTC, indicating that these factors may not be associated with trip-related fall risk with healthy aging.

Artificial neural networks (ANNs) are becoming a regular tool to support biomechanical methods, while physics-based models are widespread to understand the mechanics of body in motion. Thus, this study aimed to demonstrate the accuracy of recurrent ANN models compared with a physics-based approach in the task of predicting ground reaction forces and net lower limb joint moments during running. An inertial motion capture system and a force plate were used to collect running biomechanics data for training the ANN. Kinematic data from optical motion capture systems, sourced from publicly available databases, were used to evaluate the prediction performance and accuracy of the ANN. The linear and angular momentum theorems were applied to compute ground reaction forces and joint moments in the physics-based approach. The main finding indicates that the recurrent ANN tends to outperform the physics-based approach significantly (P < .05) at similar and higher running velocities for which the ANN was trained, specifically in the anteroposterior, vertical, and mediolateral ground reaction forces, as well as for the knee and ankle flexion moments, and hip abduction and rotation moments. Furthermore, this study demonstrates that the trained recurrent ANN can be used to predict running kinetic data from kinematics obtained with different experimental techniques and sources.

The aim of this study was to explore the association between pelvic floor dysfunction and running kinetics and pelvic acceleration in a cohort of postpartum women. The Australian Pelvic Floor Questionnaire was used to quantify symptom severity (mean [SD]: 6  [ 4] out of 40; range: 1–14) in 25 postpartum women. Participants completed a pelvic floor muscle assessment to measure pelvic muscle strength and endurance, then completed a 7-minute treadmill running protocol at a speed of 10 km·h⁻¹ to evaluate their running kinetics and pelvic acceleration. After the run, participants responded to a modified version of the symptom’s component of the PFD-SENTINEL screening tool. Mean pelvic muscle strength and endurance were 3 (1) and 9 (2), respectively. We found no significant association between PFD symptom severity and running kinetic (P = .209–.410) or pelvic acceleration (P = .081–.947) outcome measures. Fifteen participants experienced at least one symptom during the treadmill protocol. Running kinetics and pelvic acceleration may not affect or be affected by symptoms of PFD. Given the relatively low symptom expression among study participants, further research in a cohort of women with higher levels of PFD is recommended.

The incidence of lower extremity injuries in collegiate distance runners is ∼20%. Identification of a runner sustaining a potential injury remains challenging. This exploratory, cross-institutional study sought to determine whether ground reaction force (GRF) characteristics during steady-state running could identify competitive collegiate distance runners who would later sustain lower extremity injuries. Normative boundaries for 10 GRF variables during braking and propulsion were established for noninjured runners using median ± scaled median absolute deviation. A subanalysis was conducted on runners with and without impact peaks in vertical GRF to mitigate the influence of impact peaks on GRF variables. We hypothesized that prior to injury, runners who later developed an injury would have more GRF variables outside of the normative boundaries than noninjured runners. Using Cliff’s method, a rank-based, nonparametric method for comparing 2 independent groups, we found no statistically significant difference between the number of variables outside the boundaries for injured and noninjured runners overall (P = .17). However, injured runners without impact peaks had more variables outside the normative boundaries than noninjured runners (P < .001). This novel analytical approach demonstrates the potential for preidentifying collegiate distance runners without impact peaks who may be at risk for injury.

Javelin throwers cannot safely throw with a long approach run often per training session. Therefore, implements of different shapes and masses are thrown from short run-ups to emulate the demands of achieving high throwing distances. This study examined the effects of different implements, thrown from various approaches, on the kinematics and kinetics of the throwing arm. The throwing motions of 6 athletes, each throwing 6 different implements were recorded using 12 infrared cameras. Kinematics and kinetics of the shoulder and elbow joints were calculated and statistically compared. The results show that lighter implement throws achieved higher release speeds, while heavier implements required greater work to be done on them. We identified significant differences for the shoulder external rotation angle (P < .001), the shoulder internal rotation (P = .040), and elbow extension (P = .003) angular velocities and the torques of the shoulder internal rotation (P = .006), horizontal flexion (P = .004), and the elbow varus (P = .008). It can be concluded that throws with balls of different masses have different angular velocities and joint torques, and therefore can be used to train speed and strength aspects of the javelin throw while using lower run-up speeds.

Historically, obstacle crossing has been studied in a laboratory setting using a dowel rod as a modality to understand how and why individuals trip and subsequently fall. The dowel features several characteristics that are optimal for research in a laboratory setting, however, it lacks applicability in real-life situations. The purpose of this study was to compare measures of obstacle crossing for the traditional laboratory obstacle (the dowel) to several real-world obstacles. Thirty healthy, young adults (23 [4] y, range: 19–35 y) completed 6 barefoot walking conditions over an 8-m instrumented walkway while motion was recorded in 3D. Participants performed unobstructed walking as familiarization trials and 5 obstructed walking conditions were presented in a randomized order: (1) dowel, (2) branch, (3) parking curb, (4) puddle, and (5) caution rope. Measures of vertical and horizontal obstacle clearance indicate that healthy young adults cross the dowel obstacle differently than they cross real-world obstacles, such as a curb, a puddle, and a caution rope but most similar to a branch. Since dowel rods have historically been used to assess obstacle crossing strategies, we encourage researchers and readers to exercise caution when extrapolating findings to real-world obstacles found in everyday life.

Greater knee adduction moment is associated with increased risk and progression of knee osteoarthritis, and this biomechanical risk factor is modulated through kinematic gait modifications. Emotions are known to influence walking kinematics and speed, but the effect of different emotions on knee mechanics is unclear. To test this, 20 healthy participants walked while instrumented gait data was recorded. Participants initially walked naturally (baseline) and then acting 4 emotional walking conditions: Anger, Happy, Fear, and Sad, in randomized order. Statistical parametric mapping with an analysis of variance model determined the extent to which emotions influenced knee joint mechanics. Results indicated both the happy (P = .009) and sad (P < .001) condition resulted in lower knee adduction moment compared with baseline. Walking both happy and sad also resulted in walking speed changes from baseline (P < .001). A secondary analysis of covariance model with speed as the covariate indicated no significant effect of emotional condition on knee adduction moment (P > .05), which suggests that the changes from baseline can be attributed to the changes in walking speed. Decreased knee adduction is associated with reduced osteoarthritis progression and increased knee function, suggesting that walking while acting different emotions, specifically happy and sad, may moderate knee osteoarthritis risk.