The interaction between the muscle fascicle and tendon components of the human soleus (SO) muscle influences the capacity of the muscle to generate force and mechanical work during walking and ...running. In the present study, ultrasound-based measurements of in vivo SO muscle fascicle behavior were combined with an inverse dynamics analysis to investigate the interaction between the muscle fascicle and tendon components over a broad range of steady-state walking and running speeds: slow-paced walking (0.7 m/s) through to moderate-paced running (5.0 m/s). Irrespective of a change in locomotion mode (i.e., walking vs. running) or an increase in steady-state speed, SO muscle fascicles were found to exhibit minimal shortening compared with the muscle-tendon unit (MTU) throughout stance. During walking and running, the muscle fascicles contributed only 35 and 20% of the overall MTU length change and shortening velocity, respectively. Greater levels of muscle activity resulted in increasingly shorter SO muscle fascicles as locomotion speed increased, both of which facilitated greater tendon stretch and recoil. Thus the elastic tendon contributed the majority of the MTU length change during walking and running. When transitioning from walking to running near the preferred transition speed (2.0 m/s), greater, more economical ankle torque development is likely explained by the SO muscle fascicles shortening more slowly and operating on a more favorable portion (i.e., closer to the plateau) of the force-length curve.
Objectives: 1) To compare lower-limb joint mechanics during running for people with traumatic brain injury (TBI) to equivalent data obtained from a group of healthy controls (HCs); and 2) To ...determine if deficits identified in biomechanical variables during running for people with TBI responded to a six-month period of rehabilitation.
Methods: Running biomechanics data were recorded from 12 people with TBI who were attending a large metropolitan rehabilitation hospital for mobility limitations, and a comparative sample of 10 HCs at baseline and six-month follow-up.
Main Measures: Average power absorbed and generated at the hip, knee and ankle joints during stance.
Results: Compared to HCs, participants with TBI at baseline ran with greater average power absorption at the hip (−0.27 W/kg vs −0.61 W/kg; p< 0.05), reduced average power absorption at the knee (−2.03 W/kg vs −1.02 W/kg; p< 0.05) and reduced average power generation at the ankle (2.86 W/kg vs 2.06 W/kg; p< 0.05). Only average power generation at the ankle improved following six-months of rehabilitation for the participants with TBI (2.06 W/kg vs 2.79 W/kg; p< 0.05).
Conclusion: For the participants with TBI in the present study, recovery of high-level mobility following rehabilitation occurred alongside an improvement in ankle joint mechanics during running.
Abstract Hamstring strains are common injuries, the majority of which occur whilst sprinting. An understanding of the biomechanical circumstances that cause the hamstrings to fail during sprinting is ...required to improve rehabilitation specificity. The aim of this study was to therefore investigate the biomechanics of an acute hamstring strain. Bilateral kinematic and ground reaction force data were captured from a sprinting athlete prior to and immediately following a right hamstring strain. Ten sprinting trials were collected: nine normal (pre-injury) trials and one injury trial. Joint angles, torques and powers as well as hamstring muscle-tendon unit lengths were computed using a three-dimensional biomechanical model. For the pre-injury trials, the right leg compared to the left displayed greater knee extension and hamstring muscle-tendon unit length during terminal swing, an increased vertical ground reaction force peak and loading rate, and an increased peak hip extensor torque and peak hip power generation during initial stance. For the injury trial, significant biomechanical reactions were evident in response to the right hamstring strain, most notably for the right leg during the proceeding swing phase after the onset of the injury. The earliest kinematic deviations in response to the injury were displayed by the trunk and pelvis during right mid-stance. Taking into account neuromuscular latencies and electromechanical delays, the stimulus for the injury must have occurred prior to right foot-strike during the swing phase of the sprinting cycle. It is concluded that hamstring strains during sprinting most likely occur during terminal swing as a consequence of an eccentric contraction.
Abstract Physical activity is recommended to mitigate the incidence of hip osteoporotic fractures by improving femoral neck strength. However, results from clinical studies are highly variable and ...unclear about the effects of physical activity on femoral neck strength. We ranked physical activities recommended for promoting bone health based on calculations of strain energy in the femoral neck. According to adaptive bone-remodeling theory, bone formation occurs when the strain energy ( S ) exceeds its homeostatic value by 75%. The potential effectiveness of activity type was assessed by normalizing strain energy by the applied external load. Tensile strain provided an indication of bone fracture. External force and joint motion data for 15 low- and high-load weight-bearing and resistance-based activities were used. High-load activities included weight-bearing activities generating a ground force above 1 body-weight and maximal resistance exercises about the hip and the knee. Calculations of femoral loads were based on musculoskeletal and finite-element models. Eight of the fifteen activities were likely to trigger bone formation, with isokinetic hip extension (Δ S =722%), one-legged long jump (Δ S =572%), and isokinetic knee flexion (Δ S =418%) inducing the highest strain energy increase. Knee flexion induced approximately ten times the normalized strain energy induced by hip adduction. Strain and strain energy were strongly correlated with the hip-joint reaction force ( R2 =0.90–0.99; p <0.05) for all activities, though the peak load location was activity-dependent. None of the exercises was likely to cause fracture. Femoral neck mechanics is activity-dependent and maximum isokinetic hip-extension and knee-flexion exercises are possible alternative solutions to impact activities for improving femoral neck strength.
Highlights • Proximal compensatory pattern normalises during rehabilitation following TBI. • Initial ankle power generation reductions significantly improved over six months. • Improved distribution ...of lower-limb power generation was associated with higher walking speeds. • Strong inverse relationship between increased ankle and reduced hip power generation.
Altered biomechanics are frequently observed following anterior cruciate ligament reconstruction (ACLR). Yet, little is known about knee‐joint loading, particularly in the patellofemoral‐joint, ...despite patellofemoral‐joint osteoarthritis commonly occurring post‐ACLR. This study compared knee‐joint reaction forces and impulses during the landing phase of a single‐leg forward hop in the reconstructed knee of people 12‐24 months post‐ACLR and uninjured controls. Experimental marker data and ground forces for 66 participants with ACLR (28 ± 6 years, 78 ± 15 kg) and 33 uninjured controls (26 ± 5 years, 70 ± 12 kg) were input into scaled‐generic musculoskeletal models to calculate joint angles, joint moments, muscle forces, and the knee‐joint reaction forces and impulses. The ACLR group exhibited a lower peak knee flexion angle (mean difference: −6°; 95% confidence interval: −10°, −2°), internal knee extension moment (−3.63 −5.29, −1.97 percentage of body weight × participant height (body weight BW × HT), external knee adduction moment (‐1.36 −2.16, −0.56% BW × HT) and quadriceps force (−2.02 −2.95, −1.09 BW). The ACLR group also exhibited a lower peak patellofemoral‐joint compressive force (−2.24 −3.31, −1.18 BW), net tibiofemoral‐joint compressive force (−0.74 −1.20, 0.28 BW), and medial compartment force (−0.76 −1.08, −0.44 BW). Finally, only the impulse of the patellofemoral‐joint compressive force was lower in the ACLR group (−0.13 −0.23, −0.03 body weight‐seconds). Lower compressive forces are evident in the patellofemoral‐ and tibiofemoral‐joints of ACLR knees compared to uninjured controls during a single‐leg forward hop‐landing task. Our findings may have implications for understanding the contributing factors for incidence and progression of knee osteoarthritis after ACLR surgery.
Abstract Stair ambulation is more physically demanding than level walking because it requires the lower-limb muscles to generate greater net joint moments. Although lower-limb joint kinematics and ...kinetics during stair ambulation have been extensively studied, relatively little is known about how the lower-limb muscles accelerate the whole-body center of mass (COM) during stair ascent and descent. The aim of the current study was to evaluate differences in muscle contributions to COM accelerations between level walking and stair ambulation in 15 healthy adults. Three-dimensional quantitative gait analysis and musculoskeletal modeling were used to calculate the contributions of the individual lower-limb muscles to the vertical, fore-aft and mediolateral accelerations of the COM (support, progression, and balance, respectively) during level walking, stair ascent and stair descent. Muscles that contribute most significantly to the acceleration of the COM during level walking (hip, knee, and ankle extensors) also dominate during stair ambulation, but with noticeable differences in coordination. In stair ascent, gluteus maximus accelerates the body forward during the first half of stance and soleus accelerates the body backward during the second half of stance, opposite to the functions displayed by these muscles in level walking. In stair descent, vasti generates backward and medial accelerations of the COM during the second half of stance, whereas it contributes minimally during this period in level walking. Gluteus medius performs similarly in controlling mediolateral balance during level walking and stair ambulation. Differences in lower-limb muscular coordination exist between stair ambulation and level walking, and our results have implications for interventions aimed at preventing stair-related falls.
Patellofemoral joint (PFJ) osteoarthritis is common following anterior cruciate ligament reconstruction (ACLR) and may be linked with altered joint loading. However, little is known about the ...cross‐sectional and longitudinal relationship between PFJ loading and osteoarthritis post‐ACLR. This study tested if altered PFJ loading is associated with prevalent and worsening early PFJ osteoarthritis post‐ACLR. Forty‐six participants (mean ± 1 SD age 26 ± 5 years) approximately 1‐year post‐ACLR underwent magnetic resonance imaging (MRI) and biomechanical assessment of their reconstructed knee. Trunk and lower‐limb kinematics plus ground reaction forces were recorded during the landing phase of a standardized forward hop. These data were input into a musculoskeletal model to calculate the PFJ contact force. Follow‐up MRI was completed on 32 participants at 5‐years post‐ACLR. Generalized linear models (Poisson regression) assessed the relationship between PFJ loading and prevalent early PFJ osteoarthritis (i.e., presence of a PFJ cartilage lesion at 1‐year post‐ACLR) and worsening PFJ osteoarthritis (i.e., incident/progressive PFJ cartilage lesion between 1‐ and 5‐years post‐ACLR). A lower peak PFJ contact force was associated with prevalent early PFJ osteoarthritis at 1‐year post‐ACLR (n = 14 30.4%; prevalence ratio: 1.37; 95% confidence interval CI: 1.02–1.85) and a higher risk of worsening PFJ osteoarthritis between 1‐ and 5‐years post‐ACLR (n = 9 28.1%; risk ratio: 1.55, 95% CI: 1.13–2.11). Young adults post‐ACLR who exhibited lower PFJ loading during hopping were more likely to have early PFJ osteoarthritis at 1‐year and worsening PFJ osteoarthritis between 1‐ and 5‐years. Clinical interventions aimed at mitigating osteoarthritis progression may be beneficial for those with signs of lower PFJ loading post‐ACLR.
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