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Background: People with femoroacetabular with femoroacetabular impingement syndrome (FAIS) often report pain during sports involving repeated sprinting. It remains unclear how sports participation influences running biomechanics in individuals with FAIS. Hypothesis: Changes in running biomechanics and/or isometric hip strength after repeated sprint exercise would be greatest in individuals with FAIS compared with asymptomatic individuals with (CAM) and without cam morphology (Control). Study Design: Controlled laboratory study. Level of Evidence: Level 3. Methods: Three-dimensional hip biomechanics during maximal running (10 m) and hip strength were measured in 49 recreationally active individuals (FAIS = 15; CAM = 16; Control = 18) before and after repeated sprint exercise performed on a nonmotorized treadmill (8-16 × 30 m). Effects of group and time were assessed for biomechanics and strength variables with repeated-measures analyses of variance. Relationships between hip pain (Copenhagen Hip and Groin Outcome Score) and changes in hip moments and strength after repeated sprint exercise were determined using Spearman’s correlation coefficients (ρ). Results: Running speed, hip flexion angles, hip flexion and extension moments, and hip strength in all muscle groups were significantly reduced from pre to post. No significant between-group differences were observed before or after repeated sprint exercise. No significant relationships (ρ = 0.04-0.30) were observed between hip pain and changes in hip moments or strength in the FAIS group. Conclusion: Changes in running biomechanics and strength after repeated sprint exercise did not differ between participants with FAIS and asymptomatic participants with and without cam morphology. Self-reported pain did not appear to influence biomechanics during running or strength after repeated sprint exercise in participants with FAIS. Clinical Relevance: A short bout of repeated sprinting may not elicit changes in running biomechanics in FAIS beyond what occurs in those without symptoms. Longer duration activities or activities requiring greater hip flexion angles may better provoke pathology-related changes in running biomechanics in people with FAIS.

Objectives To quantify the changes in work done by lower limb joint moments during maximal speed running following a sports-specific repeated running protocol. Design Observational with repeated-measures. Methods Recreational athletes (n = 18 (9 females), aged = 26.2 ± 6.2 years) performed 12 maximal 30-m sprints on a non-motorised treadmill. Three-dimensional kinematics and ground reaction forces were subsequently recorded during a 10-m maximal overground sprint before and immediately after the repeated running protocol, from which we calculated work done by sagittal plane hip, knee, and ankle moments. Relative work (J/kg) was reported as a percentage of positive and negative work done by the sum of joint moments. Results Following the repeated running protocol, maximal sprint speed decreased by 19% and was accompanied by reductions in total positive (−1.47 J/kg) and negative (−0.92 J/kg) work, in addition to work done by hip (−0.43 to −0.82 J/kg) and knee (−0.28 J/kg) moments during swing. Compared to before the repeated running protocol, less relative work was done by hip (−9%) and knee (−3%) extension moments during swing. Reductions in work done by hip and knee joint moments during swing were significantly correlated with reductions in maximum running speed (r = 0.61−0.89, p Conclusions A sports-specific repeated running protocol resulted in reductions in mechanical work done by sagittal plane hip and knee joint moments during maximal overground sprinting. Interventions focused on maintaining positive work done by the hip flexors/extensors and negative work done by knee flexors/extensors during the swing phase of running may help prevent reductions in speed following repeated sprinting.

Background: Walking speed is a confounding factor in biomechanical analyses of gait, but still many studies compare gait biomechanics at comfortable walking speed (CWS) that is likely to differ between groups or conditions. To identify gait deviation unrelated to walking speed, methods are needed to correct biomechanical data over the gait cycle for walking speed. Research question: How to compare knee kinetics over the gait cycle at different walking speeds? Methods: 22 asymptomatic subjects walked on a dual-belt treadmill at CWS and 4 fixed speeds. Knee moments in sagittal (KFM) and frontal plane (KAM) were calculated via inverse dynamics. The net moment differences between CWS and fixed speed were expressed as a root-mean-square error (RMSE) normalized to the range of the variable. Two methods to correct for walking speed were compared. In method 1, KFM and KAM values were estimated based on interpolation between speeds at each percentage of the gait cycle. In method 2, principal component analysis was used to extract speed related features to reconstruct KFM and KAM at the speed of interest. The accuracy of both methods was tested using a leave-one-out cross validation. Results: Walking speed influenced the magnitude and shape of KFM and KAM. To account for these speed influences using both methods, leave-one-out cross validation showed low normalized RMSE (< 5 %), with little difference between the two methods. RMSE for both reconstruction methods were up to 60 % lower than the RMSE between CWS and fixed speed. Significance: Both methods could accurately correct knee kinetics over the gait cycle for the effects of walking speed. Walking speed dependency should be incorporated in each gait laboratory's reference dataset to be able to identify gait deviations unrelated to gait speed.

Objective: This study determined whether the deep hip muscles could contribute to hip stability. Methods: Hip stability was defined as rotational hip stiffness in the sagittal plane, which was calculated for walking trials for 12 participants via electromyography (EMG)informed neuromusculoskeletal modelling that included all 22 hip spanning muscles. Three model configurations were compared that differed in the excitations of the deep hip muscles, but were identical in the excitations of all other muscles: (1) deep hip muscles informed by intramuscular EMG measurements (assisted activation); (2) deep hip muscles with simulated zero activation (no activation); (3) deep hip muscles with simulated maximal activation (maximal activation). Sagittal plane rotational hip stiffness over the gait cycle was compared between model configurations using a within-participant analysis of variance via statistical parametric mapping (p

The deep hip muscles are often omitted in studies investigating hip contact forces using neuromusculoskeletal modelling methods. However, recent evidence indicates the deep hip muscles have potential to change the direction of hip contact force and could have relevance for hip contact loading estimates. Further, it is not known whether deep hip muscle excitation patterns can be accurately estimated using neuromusculoskeletal modelling or require measurement (through invasive and time-consuming methods) to inform models used to estimate hip contact forces. We calculated hip contact forces during walking, squatting, and squat-jumping for 17 participants using electromyography (EMG)-informed neuromusculoskeletal modelling with (informed) and without (synthesized) intramuscular EMG for the deep hip muscles (piriformis, obturator internus, quadratus femoris). Hip contact force magnitude and direction, calculated as the angle between hip contact force and vector from femoral head to acetabular center, were compared between configurations using a paired t-test deployed through statistical parametric mapping (P 0.05). Additionally, root mean square error, correlation coefficients (R

A better understanding of deep hip muscle function is needed to establish whether retraining and strengthening these muscles is a worthwhile target for rehabilitation. This study aimed to determine the contribution of the deep hip muscles to the direction of hip loading in the acetabulum. Hip contact forces were calculated during walking and squatting for 12 participants (age: 24 ± 4 yrs, 4 females) using electromyography-informed neuromusculoskeletal modelling. Models were configured with different deep hip muscle activation levels: deep hip muscles (piriformis, obturator internus and externus, gemellus superior and inferior, and quadratus femoris) informed by intramuscular electromyography measurements (i.e., normal activation; assisted activation) and simulated with zero (no activation) or maximal (maximal activation) activation. The angle between the hip contact force and the vector from the femoral head to the acetabular center (hip contact force angle) was calculated for all configurations, where lower angles equated to hip loading directed towards the acetabular center. The position and spread of acetabular loading during both tasks were calculated for all configurations and compared using a within-participant analysis of variance via statistical parametric mapping (P 0.05). Maximal activation resulted in lower hip contact force angles and more anterior-inferior oriented, albeit a slightly reduced, spread of acetabular loading compared to assisted activation and no activation. Results suggest that, if activated maximally, the deep hip muscles can change the direction of hip loading away from commonly damaged areas of acetabular cartilage. Targeted training of these muscles may be relevant for individuals with hip pathology who present with unfavorable regional loading and/or cartilage lesions.