Running footwear is continuously being modified and improved; however, running-related overuse injury rates remain high. Nevertheless, novel manufacturing processes enable the production of individualized running shoes that can fit the individual needs of runners, with the potential to reduce injury risk. For this reason, it is essential to investigate functional groups of runners, a collective of runners who respond similarly to a footwear intervention. Therefore, the objective of this study was to develop a framework to identify functional groups based on their individual footwear response regarding injury-specific running-related risk factors for Achilles tendinopathy, Tibial stress fractures, Medial tibial stress syndrome, and Patellofemoral pain syndrome. In this work, we quantified the footwear response patterns of 73 female and male participants when running in three different footwear conditions using unsupervised learning (k-means clustering). For each functional group, we identified the footwear conditions minimizing the injury-specific risk factors. We described differences in the functional groups regarding their running style, anthropometric, footwear perception, and demographics. The results implied that most functional groups showed a tendency for a single footwear condition to reduce most biomechanical risk factors for a specific overuse injury. Functional groups often differed in their hip and pelvis kinematics as well as their subjective rating of the footwear conditions. The footwear intervention only partially affected biomechanical risk factors attributed to more proximal joints. Due to its adaptive nature, the framework could be applied to other footwear interventions or performance-related biomechanical variables.

BACKGROUND:Internal tibial loading is influenced by modifiable factors with implications for the risk of stress injury. Runners encounter varied surface steepness (gradients) when running outdoors and may adapt their speed according to the gradient. This study aimed to quantify tibial bending moments and stress at the anterior and posterior peripheries when running at different speeds on surfaces of different gradients. METHODS:Twenty recreational runners ran on a treadmill at 3 different speeds (2.5 m/s, 3.0 m/s, and 3.5 m/s) and gradients (level: 0%; uphill: +5%, +10%, and +15%; downhill: -5%, -10%, and -15%). Force and marker data were collected synchronously throughout. Bending moments were estimated at the distal third centroid of the tibia about the medial-lateral axis by ensuring static equilibrium at each 1% of stance. Stress was derived from bending moments at the anterior and posterior peripheries by modeling the tibia as a hollow ellipse. Two-way repeated-measures analysis of variance were conducted using both functional and discrete statistical analyses. RESULTS:There were significant main effects for running speed and gradient on peak bending moments and peak anterior and posterior stress. Higher running speeds resulted in greater tibial loading. Running uphill at +10% and +15% resulted in greater tibial loading than level running. Running downhill at -10% and -15% resulted in reduced tibial loading compared to level running. There was no difference between +5% or -5% and level running. CONCLUSION:Running at faster speeds and uphill on gradients ≥+10% increased internal tibial loading, whereas slower running and downhill running on gradients ≥-10% reduced internal loading. Adapting running speed according to the gradient could be a protective mechanism, providing runners with a strategy to minimize the risk of tibial stress injuries.

Injury prevention is essential in running due to the risk of overuse injury development. Tailoring running shoes to individual needs may be a promising strategy to reduce this risk. Novel manufacturing processes allow the production of individualised running shoes that incorporate features that meet individual biomechanical and experiential needs. However, specific ways to individualise footwear to reduce injury risk are poorly understood. Therefore, this scoping review provides an overview of (1) footwear design features that have the potential for individualisation; and (2) the literature on the differential responses to footwear design features between selected groups of individuals. These purposes focus exclusively on reducing the risk of overuse injuries. We included studies in the English language on adults that analysed: (1) potential interaction effects between footwear design features and subgroups of runners or covariates (e.g., age, sex) for running-related biomechanical risk factors or injury incidences; (2) footwear comfort perception for a systematically modified footwear design feature. Most of the included articles (n = 107) analysed male runners. Female runners may be more susceptible to footwear-induced changes and overuse injury development; future research should target more heterogonous sampling. Several footwear design features (e.g., midsole characteristics, upper, outsole profile) show potential for individualisation. However, the literature addressing individualised footwear solutions and the potential to reduce biomechanical risk factors is limited. Future studies should leverage more extensive data collections considering relevant covariates and subgroups while systematically modifying isolated footwear design features to inform footwear individualisation. Individualised footwear bears the potential to alter biomechanics and, subsequently, the individual injury risk profile. Since different footwear modifications modulate risk factors for specific overuse injuries diffently, individualised footwear solutions must be designed for specific overuse injuries by targeting injury-specific biomechanical risk factors. The influence of various footwear modifications on biomechanical risk factors concerning environmental constraints, athlete anthropometry, and experience level has been documented only to a limited extent and requires further research. In addition to minimising biomechanical risk factors, the comfort and fit of the shoe should be considered to design an individually optimal shoe.

Background Running overuse injuries (ROIs) occur within a complex, partly injury-specific interplay between training loads and extrinsic and intrinsic risk factors. Biomechanical risk factors (BRFs) are related to the individual running style. While BRFs have been reviewed regarding general ROI risk, no systematic review has addressed BRFs for specific ROIs using a standardized methodology. Objective To identify and evaluate the evidence for the most relevant BRFs for ROIs determined during running and to suggest future research directions. Design Systematic review considering prospective and retrospective studies. (PROSPERO_ID: 236,832). Data Sources PubMed. Connected Papers. The search was performed in February 2021. Eligibility Criteria English language. Studies on participants whose primary sport is running addressing the risk for the seven most common ROIs and at least one kinematic, kinetic (including pressure measurements), or electromyographic BRF. A BRF needed to be identified in at least one prospective or two independent retrospective studies. BRFs needed to be determined during running. Results Sixty-six articles fulfilled our eligibility criteria. Levels of evidence for specific ROIs ranged from conflicting to moderate evidence. Running populations and methods applied varied considerably between studies. While some BRFs appeared for several ROIs, most BRFs were specific for a particular ROI. Most BRFs derived from lower-extremity joint kinematics and kinetics were located in the frontal and transverse planes of motion. Further, plantar pressure, vertical ground reaction force loading rate and free moment-related parameters were identified as kinetic BRFs. Conclusion This study offers a comprehensive overview of BRFs for the most common ROIs, which might serve as a starting point to develop ROI-specific risk profiles of individual runners. We identified limited evidence for most ROI-specific risk factors, highlighting the need for performing further high-quality studies in the future. However, consensus on data collection standards (including the quantification of workload and stress tolerance variables and the reporting of injuries) is warranted.

Patrick Mai, Leon Robertz, Johanna Robbin, Matthias Thelen, Markus Kurz, Matthieu B. Trudeau, Gillian Weir, Joseph Hamill and Steffen Willwacher Institute for Biomechanics and Orthopaedics, German Sports University Cologne, K€oln, Germany; Department of Mechanical and Process Engineering, Offenburg University, Offenburg, Germany; Faculty of Human Science, Sports Tech Research Centre, Mid Sweden University, Ostersund, Sweden; Brooks Sports Inc, Seattle, WA, USA; Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, USA

Treadmills are essential to the study of human and animal locomotion as well as for applied diagnostics in both sports and medicine. The quantification of relevant biomechanical and physiological variables requires a precise regulation of treadmill belt velocity (TBV). Here, we present a novel method for time-efficient tracking of TBV using standard 3D motion capture technology. Further, we analyzed TBV fluctuations of four different treadmills as seven participants walked and ran at target speeds ranging from 1.0 to 4.5 m/s. Using the novel method, we show that TBV regulation differs between treadmill types, and that certain features of TBV regulation are affected by the subjects' body mass and their locomotion speed. With higher body mass, the TBV reductions in the braking phase of stance became higher, even though this relationship differed between locomotion speeds and treadmill type (significant body mass × speed × treadmill type interaction). Average belt speeds varied between about 98 and 103% of the target speed. For three of the four treadmills, TBV reduction during the stance phase of running was more intense (> 5% target speed) and occurred earlier (before 50% of stance phase) unlike the typical overground center of mass velocity patterns reported in the literature. Overall, the results of this study emphasize the importance of monitoring TBV during locomotor research and applied diagnostics. We provide a novel method that is freely accessible on Matlab's file exchange server ("getBeltVelocity.m") allowing TBV tracking to become standard practice in locomotion research.

The aim of this study was to investigate the influence of slope and speed on lower-limb kinematics and energy cost of running. Six well-trained runners (VO 2max 72 ± 6 mL·kg −1 ·min −1 ) were recruited for the study and performed (1) VO 2max and energy cost tests and (2) an experimental running protocol at two speeds, 12 km·h −1 and a speed corresponding to 80% of VO 2max (V80, 15.8 ± 1.3 km·h −1 ) on three different slopes (0°, −5°, and −10°), totaling six 5-min workload conditions. The workload conditions were randomly ordered and performed continuously. The tests lasted 30 min in total. All testing was performed on a large treadmill (3 × 5 m) that offered control over both speed and slope. Three-dimensional kinematic data of the right lower limb were captured during the experimental running protocol using eight infrared cameras with a sampling frequency of 150 Hz. Running kinematics were calculated using a lower body model and inverse kinematics approach. The generic model contained three, one, and two degrees of freedom at the hip, knee, and ankle joints, respectively. Oxygen uptake was measured throughout the experimental protocol. Maximum hip extension and flexion during the stance phase increased due to higher speed ( p < 0.01 and p < 0.01, respectively). Knee extension at the touchdown and maximal knee flexion in the stance phase both increased on steeper downhill slopes (both p < 0.05). Ground contact time (GCT) decreased as the speed increased ( p < 0.01) but was unaffected by slope ( p = 0.73). Runners modified their hip movement pattern in the sagittal plane in response to changes in speed, whereas they altered their knee movement pattern during the touchdown and stance phases in response to changes in slope. While energy cost of running was unaffected by speed alone ( p = 0.379), a shift in energy cost was observed for different speeds as the downhill gradient increased ( p < 0.001). Energy cost was lower at V80 than 12 km·h −1 on a −5° slope but worse on a −10° slope. This indicates that higher speeds are more efficient on moderate downhill slopes (−5°), while lower speeds are more efficient on steeper downhill slopes (−10°).

The purpose of this study was to investigate fatigue-related changes in spinal kinematics, kinetics, and muscle activity of back muscles during a 2000 m all-out ergometer rowing performance. We analyzed ten male subjects with experience in both rowing and CrossFit exercises. We applied a novel kinematic method to describe spine curvature, determined bending moments at the spine using inverse dynamics and collected EMG data. We identified significant increases in spine curvature of the thoracic spine (i.e. vertebrae Th6 to Th11). Significant increases in peak moments were found only at the upper spine (i.e. Th2). We found no significant changes in EMG amplitudes, while the frequency analysis showed significant decreases in the mean frequencies (MNF) for the M. latissimus dorsi, the M. trapezius descendens and the M. deltoideus posterior. No significant changes on MNF were found for the Mm. erector spinae. We hypothesize that the significant increase in curvature for the thoracic spine is connected to the fatigued back muscles, especially the Mm. trapezius descendens, and might lead to an unbalanced loading of intervertebral discs and other structures. These findings are particularly important for athletes and coaches in CrossFit as strenuous rowing intervals are combined with technical exercises with high loads on the back and spine (e.g. power and Olympic lifting) leading to impaired muscular stabilization and potentially to an increased injury risk.

Running technique is often classified based on the initial foot contact in the sagittal plane (i.e. the foot-strike pattern). Nonetheless, observations suggest that there is also variability betwee...

In biomechanics research, inverse dynamics (ID) is a standard tool to calculate net joint moments (JMs). Altered frontal plane knee kinetics, particularly internal peak abduction moments (KAMs) and abduction impulse, are linked to increased injury risk in distance running (Stefanyshyn, Stergiou, Lun, Meeuwisse, & Worobets, 2006; Stickley, Presuto, Radzak, Bourbeau, & Hetzler, 2018). Therefore, footwear design might be guided by reducing KAM magnitude and shoe conditions could be ranked by their effects on KAM. However, because of inherent noise in marker trajectory and ground reaction force (GRF) data, there is a need for low pass filtering these signals. There is no cross-study consistency in the choice of cut-off frequencies (fc), even if it has been shown that differences in fc for kinematic and kinetic data can lead to non-physiological fluctuations in JMs.

BACKGROUND:The aim of this study was to identify the acute hormonal responses of salivary testosterone (T) and cortisol (C) concentrations during and after two different resistance exercises involving the lower and the upper body, respectively.METHODS:For this reason, 13 healthy recreationally trained male athletes performed an identical strength protocol (5x10 reps, with ~75% of 1 RM) with the exercises bench press and back-squat in a cross-over design. Saliva samples were taken at baseline (t0), mid training (t1), immediately after (t2), 15 (t3) and 45 minutes after the training (t4). Samples were analyzed for T and C, and the T/C ratio was calculated.RESULTS:T concentrations increased significantly from t0 to t2, t3 and t4 and also at t3 and t4 for C in the back-squat protocol (P<0.05). There were no significant changes for T and C in the bench press protocol (P<0.05). The T/C ratio remained constant for the bench press protocol. The T/C ratio increased in the squat protocol at t2 and decreased at t3 and t4.CONCLUSIONS:We conclude that back-squat exercise can change the hormonal state of the body after an intense resistance training workout, while an exercise with a lower amount of muscle mass (i.e. bench press) has almost no influence on T and C.

The purpose of the present study was to investigate the effects of fatigue on lower back loading and pelvis kinematics in distance running. Kinetic and kinematic data of the whole body was recorded for 13 subjects during a near-maximal 10-km run. Pelvis kinematics were calculated in 3D while moments acting on the lumbar spine were determined by using a full body lumbar spine model in OpenSim. We found significant effects of running distance for pelvis kinematics in the transverse and sagittal plane whereas the lumbar spine moments increased significantly in the frontal and transverse plane. These results support earlier findings suggesting a connection between running and spinal or pelvic overuse injuries. Thus, distance runners should focus on a controlled arm swing and upper body rotation as well as pelvis stabilization.

Longitudinal bending stiffness (LBS) of footwear has been shown to affect performance in jumping and sprinting tasks. A detailed description of the mechanisms underlying these performance alterations is lacking in the literature at the moment. Therefore, the purpose of this study is to describe why performance in a linear acceleration task is affected by LBS. Fifteen male athletes were analysed using full-body motion analysis combined with ground reaction force (GRF) measurements during the first step of a full effort 5 m sprint in a low stiffness baseline (BL), medium stiffness (MS) and high stiffness (HS) condition. A significant reduction in acceleration performance (6.3%) was found in the HS condition compared to BL. Changes in acceleration performance in MS and HS were related to altered contact times, ground force application and overall body orientation, but not to alterations in energy absorption at the metatarsal phalangeal (MTP) joint. A gearing function of LBS was evident from increased MTP and ankle joint GRF lever arms, which might offer a potential to improve the effectiveness of horizontal force application. Nonetheless, athletes in this study were not using this potential to improve acceleration performance, possibly due to missing strength capacities. The results of this study indicate that high LBS might lead to reduced acceleration performance in athletes lacking the capacities to make use of the gearing function of footwear LBS. Footwear studies need to address the interrelationship between LBS, individual strength capacities, average ground force application and its effectiveness during acceleration tasks in the future.