Leg Stiffness and Vertical Stiffness of Habitual Forefoot and Rearfoot Strikers during Running

Hamstring stiffness and injury risk factors during the handball season in female players

Monitoring the muscle mechanical properties and functions of female athletes throughout their training season is relevant to understand the relationships between these factors and to predict noncontact injuries, which are prevalent among female athletes. The first aim of this study was to determine whether female handball players' passive stiffness of the hamstring muscles is associated with hamstring extensibility, strength of knee flexors and extensors, and lower limb stiffness. Additionally, the study monitored fluctuations in these factors over 25 weeks. The study utilized an isokinetic dynamometer to record hamstring passive stiffness, extensibility, and hamstring and quadriceps strength of 18 young handball players. Lower limb stiffness was determined from a countermovement vertical jump conducted on a force plate. The countermovement jump involved the calculation of the peak force during the eccentric phase and the mean force during the concentric phase. The results showed a positive correlation between hamstring passive stiffness and lower limb stiffness (r = 0.660, p < 0.01), knee flexion and extension strength (r = 0.592, p < 0.01 and r = 0.497, p < 0.05, respectively), and eccentric peak force (r = 0.587, p < 0.01) during jumping. The strength of knee extensors increased significantly after 6 weeks, and hamstring stiffness after 12 weeks of training. In conclusion, the increased hamstring stiffness following training did not match other factors associated with injury risk. Therefore, preventing multifactorial injury risk requires a comprehensive approach, and monitoring one factor alone is insufficient to predict noncontact injuries in female handball players.

Assessing the effects of foot strike patterns and shoe types on the control of leg length and orientation in running

This research investigates the stabilization of leg length and orientation during the landing phase of running, examining the effects of different footwear and foot strike patterns. Analyzing kinematic data from twenty male long-distance runners, both rearfoot and forefoot strikers, we utilized the Uncontrolled Manifold approach to assess stability. Findings reveal that both leg length and orientation are indeed stabilized during landing, challenging the hypothesis that rearfoot strikers exhibit less variance in deviations than forefoot strikers, and that increased footwear assistance would reduce these deviations. Surprisingly, footwear with a lower minimalist index enhanced post-landing stability, suggesting that cushioning contributes to both force dissipation and leg length stability. The study indicates that both foot strike patterns are capable of effectively reducing task-relevant variance, with no inherent restriction on flexibility for rearfoot strikers. However, there is an indication of potential reliance on footwear for stability. These insights advance our understanding of the biomechanics of running, highlighting the role of footwear in stabilizing leg length and orientation, which has significant implications for running efficiency and injury prevention.

Lower limb vertical stiffness and frontal plane angular impulse during perturbation-induced single limb stance and their associations with gait in individuals post-stroke

After stroke, deficits in paretic single limb stance (SLS) are commonly observed and affect walking performance. During SLS, the hip abductor musculature is critical in providing vertical support and regulating balance. Although disrupted paretic hip abduction torque production has been identified in individuals post-stroke, interpretation of previous results is limited due to the discrepancies in weight-bearing conditions. Using a novel perturbation-based assessment that could induce SLS by removing the support surface underneath one limb, we aim to investigate whether deficits in hip abduction torque production, vertical body support, and balance regulation remain detectable during SLS when controlling for weight-bearing, and whether these measures are associated with gait performance. Our results showed that during the perturbation-induced SLS, individuals post-stroke had lower hip abduction torque, less vertical stiffness, and increased frontal plane angular impulse at the paretic limb compared to the non-paretic limb, while no differences were found between the paretic limb and healthy controls. In addition, vertical stiffness during perturbation-induced SLS was positively correlated with single support duration during gait at the paretic limb and predicted self-selected and fast walking speeds in individuals post-stroke. The findings indicate that reduced paretic hip abduction torque during SLS likely affects vertical support and balance control. Enhancing SLS hip abduction torque production could be an important rehabilitation target to improve walking function for individuals post-stroke.

Lower Limb Vertical Stiffness and Frontal Plane Angular Impulse during Perturbation-Induced Single Limb Stance and Their Associations with Gait in Individuals Post-Stroke

Background

After stroke, deficits in paretic single limb stance (SLS) are commonly observed and affect walking performance. During SLS, the hip abductor musculature is critical in providing vertical support and regulating balance. Although disrupted paretic hip abduction torque production has been identified in individuals post-stroke, interpretation of previous results is limited due to the discrepancies in weight-bearing conditions.

Objective

To investigate whether deficits in hip abduction torque production, vertical body support, and balance regulation remain during SLS when controlling for weight-bearing using a perturbation-based assessment, and whether these measures are associated with gait performance.

Methods

We compared hip abduction torque, vertical stiffness, and frontal plane angular impulse between individuals post-stroke and healthy controls when SLS was induced by removing the support surface underneath one limb. We also tested for correlations between vertical stiffness and angular impulse during perturbation-induced SLS and gait parameters during overground walking.

Results

During the perturbation-induced SLS, lower hip abduction torque, less vertical stiffness, and increased frontal plane angular impulse were observed at the paretic limb compared to the non-paretic limb, while no differences were found between the paretic limb and healthy controls. Vertical stiffness during perturbation-induced SLS was positively correlated with single support duration during gait at the paretic limb and predicted self-selected and fast walking speeds in individuals post-stroke.

Conclusions

Reduced paretic hip abduction torque during SLS likely affects vertical support and balance control. Enhancing SLS hip abduction torque production could be an important rehabilitation target to improve walking function for individuals post-stroke.

Validity and reliability of inertial measurement units measurements for running kinematics in different foot strike pattern runners

This study aimed to assess the validity and reliability of the three-dimensional joint kinematic outcomes obtained by the inertial measurement units (IMUs) for runners with rearfoot strike pattern (RFS) and non-rearfoot strike pattern (NRFS). The IMUs system and optical motion capture system were used to simultaneous collect 3D kinematic of lower extremity joint data from participants running at 12 km/h. The joint angle waveforms showed a high correlation between the two systems after the offset correction in the sagittal plane (NRFS: coefficient of multiple correlation (CMC) = 0.924-0.968, root mean square error (RMSE) = 4.6^°-13.7^°; RFS: CMC = 0.930-0.965, RMSE = 3.1^°-7.7^°), but revealed high variability in the frontal and transverse planes (NRFS: CMC = 0.924-0.968, RMSE = 4.6°-13.7°; RFS: CMC = 0.930-0.965, RMSE = 3.1°-7.7°). The between-rater and between-day reliability were shown to be very good to excellent in the sagittal plane (between-rater: NRFS: CMC = 0.967-0.975, RMSE = 1.9°-2.9°, RFS: CMC = 0.922-0.989, RMSE = 1.0°-2.5°; between-day: NRFS: CMC = 0.950-0.978, RMSE = 1.6°-2.7°, RFS: CMC = 0.920-0.989, RMSE = 1.7°-2.2°), whereas the reliability was weak to very good (between-rater: NRFS: CMC = 0.480-0.947, RMSE = 1.1°-2.7°, RFS: CMC = 0.646-0.873, RMSE = 0.7°-2.4°; between-day: NRFS: CMC = 0.666-0.867, RMSE = 0.7°-2.8°, RFS: CMC = 0.321-0.805, RMSE = 0.9°-5.0°) in the frontal and transverse planes across all joints in both types of runners. The IMUs system was a feasible tool for measuring lower extremity joint kinematics in the sagittal plane during running, especially for RFS runners. However, the joint kinematics data in frontal and transverse planes derived by the IMUs system need to be used with caution.

Leg stiffness during running in highly cushioned shoes with a carbon-fiber plate and traditional shoes

BACKGROUND

Nike ZoomX Vaporfly (NVF) improves running economy and performance. The biomechanical mechanisms of these shoes are not fully understood, although thicker midsoles and carbon fiber plates are considered to play an important role in the spring-like leg characteristics during running. Leg stiffness (k_leg) in the spring-mass model has been commonly used to investigate spring-like running mechanics during running.

RESEARCH QUESTION

Does k_leg during running differ between NVF and traditional (TRAD) shoes?

METHODS

Eighteen male habitual forefoot and/or midfoot strike runners ran on a treadmill at 20 km/h with NVF and TRAD shoes, respectively. k_leg, vertical oscillation of the center of mass (∆CoM), spatiotemporal parameters, and mechanical loading were determined.

RESULTS

k_leg was 4.8% lower in the NVF shoe condition than in the TRAD condition, although no significant difference was observed. ∆CoM was not significantly different between shoe conditions. Spatiotemporal parameters and mechanical loading were also not significantly different between shoe conditions.

SIGNIFICANCE

The NVF shoe is well known as improving the running economy and running performance for the cause by characteristics of better spring function. Contrary to expectation, k_leg and other parameters were not significantly different during running in the NVF compared to TRAD shoe at 20 km/h. These findings indicate that well-trained runners' spring-like running mechanics would not alter even if wearing the NVF shoes.

Application of Leg, Vertical, and Joint Stiffness in Running Performance: A Literature Overview

Stiffness, the resistance to deformation due to force, has been used to model the way in which the lower body responds to landing during cyclic motions such as running and jumping. Vertical, leg, and joint stiffness provide a useful model for investigating the store and release of potential elastic energy via the musculotendinous unit in the stretch-shortening cycle and may provide insight into sport performance. This review is aimed at assessing the effect of vertical, leg, and joint stiffness on running performance as such an investigation may provide greater insight into performance during this common form of locomotion. PubMed and SPORTDiscus databases were searched resulting in 92 publications on vertical, leg, and joint stiffness and running performance. Vertical stiffness increases with running velocity and stride frequency. Higher vertical stiffness differentiated elite runners from lower-performing athletes and was also associated with a lower oxygen cost. In contrast, leg stiffness remains relatively constant with increasing velocity and is not strongly related to the aerobic demand and fatigue. Hip and knee joint stiffness are reported to increase with velocity, and a lower ankle and higher knee joint stiffness are linked to a lower oxygen cost of running; however, no relationship with performance has yet been investigated. Theoretically, there is a desired “leg-spring” stiffness value at which potential elastic energy return is maximised and this is specific to the individual. It appears that higher “leg-spring” stiffness is desirable for running performance; however, more research is needed to investigate the relationship of all three lower limb joint springs as the hip joint is often neglected. There is still no clear answer how training could affect mechanical stiffness during running. Studies including muscle activation and separate analyses of local tissues (tendons) are needed to investigate mechanical stiffness as a global variable associated with sports performance.