The "impacts cause injury" hypothesis: Running in circles or making new strides?

Can Ground Reaction Force Variables Preidentify the Probability of a Musculoskeletal Injury in Collegiate Distance Runners?

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.

Effect of double- density foot orthoses on ground reaction forces and lower limb muscle activities during running in adults with and without pronated feet

BACKGROUND

The analysis of ground reaction forces and muscle activities during walking or running can help clinicians decide on the usage of foot orthoses, particularly in individuals with pronated feet. Here, we aimed to investigate the effects of double- density foot orthoses on running kinetics and lower limb muscle activities in adults with and without pronated feet.

METHODS

Forty male adults with pronated feet (PF: n = 20, age = 25.4 ± 0.3 years, body-mass-index [BMI] = 23.3 ± 1.2 kg/m2) and without pronated feet (WPF: n = 20, age = 26.4 ± 1.0 years, BMI = 24.0 ± 0.7 kg/m2) volunteered to participate in this study. The study was registered with the Iranian Registry of Clinical Trials (IRCT20220129053865N1). Ground reaction forces (Fx, Fy, Fz) and lower limb muscle activities (e.g., m. gastrocnemius) were recorded using surface electromyography (EMGs) during running at a constant speed of 3.2 m/s over an 18-m walkway with an embedded force plate. EMGs were normalized to maximum voluntary isometric contractions.

RESULTS

Test-retest reliability for running speed data was excellent for PF and WPF groups and for the entire study cohort with intraclass correlation coefficients > 0.95. The 2-way ANOVA revealed lower peak Fz (p = 0.011; d = 1.226), lower time-to-peak for Fx (p = 0.023, d = 1.068), Fy (p = 0.025, d = 1.056), and Fz (p = 0.045, d = 0.931) during running with foot orthoses in PF individuals. During the loading phase, PF and WPF exhibited lower gastrocnemius (WPF: p = 0.005, d = 1.608; PF: p = 0.001, d = 2.430 ) and vastus medialis (WPF: p < 0.001, d = 2.532; PF: p < 0.001, d = 2.503) activity when running with foot orthoses.

CONCLUSIONS

Although double- density foot orthoses resulted in some beneficial biomechanical effects such as lower muscle activation (e.g., m. vastus medialis) in individuals with PF, foot orthoses constructions need further modifications to achieve even better running mechanics to enhance performance and lower limbinjury occurrence.

TRIAL REGISTRATION

IRCT20220129053865N1 (Registration date 19/08/2024).

Influence of Total Running Experience on Lower Leg Variability: Implications for Control and Performance in Male Athletes

This study investigates the relationship between total running experience, defined as cumulative years of running multiplied by weekly mileage, and variability in lower leg joint kinematics during treadmill running. Twenty-seven male athletes participated, running while kinematic and kinetic data were collected. Linear regression revealed significant negative correlations between total running experience and variability in both knee and ankle joint range of motion (ROM). Specifically, ankle ROM variability (p = 0.001, R2 = 0.35) and knee ROM variability (p = 0.002, R2 = 0.32) were reduced in runners with more experience. A stepwise regression model further identified ankle ROM variability as a significant predictor (p = 0.033), explaining 44.25% of the variance in total running experience. A significant positive correlation between running experience and instantaneous vertical loading rate (IVLR) (p = 0.025, R2 = 0.15) suggests that more experienced runners generate higher load rates. These findings indicate that more experienced runners exhibit more consistent and stable movement patterns, reflecting refined motor control. The results support the hypothesis that greater running experience is associated with reduced variability in movement patterns within a controlled environment, providing insights into the mechanisms that could contribute to enhanced performance and injury prevention.

Influence of Sudden Changes in Foot Strikes on Loading Rate Variability in Runners

Foot strike patterns influence vertical loading rates during running. Running retraining interventions often include switching to a new foot strike pattern. Sudden changes in the foot strike pattern may be uncomfortable and may lead to higher step-to-step variability. This study evaluated the effects of running with an imposed and usual foot strike on vertical loading rate variability and amplitude. Twenty-seven participants (16 men and 11 women; age range: 18-30 years) ran on an instrumented treadmill with their usual foot strike for 10 min. Then, the participants were instructed to run with an unusual foot strike for 6 min. We calculated the vertical instantaneous and vertical average loading rates and their variances over 200 steps to quantify vertical loading rate variability. We also calculated the amplitude and variability of the shank acceleration peak using an inertial measurement unit. The vertical loading rate and shank acceleration peak amplitudes were higher when running with a rearfoot strike, regardless of the foot strike conditions (i.e., usual or imposed). The vertical loading rate and shank acceleration peak variability were higher when running with an imposed rearfoot strike than when running with a usual forefoot strike. No differences were found in the vertical loading rate and shank acceleration peak variabilities between the imposed forefoot strike and usual rearfoot strike conditions. This study offers compelling evidence that adopting an imposed (i.e., unusual) rearfoot strike amplifies loading rate and shank acceleration peak variabilities.

Predicting overstriding with wearable IMUs during treadmill and overground running

Running injuries are prevalent, but their exact mechanisms remain unknown largely due to limited real-world biomechanical analysis. Reducing overstriding, the horizontal distance that the foot lands ahead of the body, may be relevant to reducing injury risk. Here, we leverage the geometric relationship between overstriding and lower extremity sagittal segment angles to demonstrate that wearable inertial measurement units (IMUs) can predict overstriding during treadmill and overground running in the laboratory. Ten recreational runners matched their strides to a metronome to systematically vary overstriding during constant-speed treadmill running and showed similar overstriding variation during comfortable-speed overground running. Linear mixed models were used to analyze repeated measures of overstriding and sagittal segment angles measured with motion capture and IMUs. Sagittal segment angles measured with IMUs explained 95% and 98% of the variance in overstriding during treadmill and overground running, respectively. We also found that sagittal segment angles measured with IMUs correlated with peak braking force and explained 88% and 80% of the variance during treadmill and overground running, respectively. This study highlights the potential for IMUs to provide insights into landing and loading patterns over time in real-world running environments, and motivates future research on feedback to modify form and prevent injury.

Use of subject-specific models to detect fatigue-related changes in running biomechanics: a random forest approach

Running biomechanics are affected by fatiguing or prolonged runs. However, no evidence to date has conclusively linked this effect to running-related injury (RRI) development or performance implications. Previous investigations using subject-specific models in running have demonstrated higher accuracy than group-based models, however, this has been infrequently applied to fatigue. In this study, two experiments were conducted to determine whether subject-specific models outperformed group-based models to classify running biomechanics during non-fatigued and fatigued conditions. In the first experiment, 16 participants performed four treadmill runs at or around the maximal lactate steady state. In the second experiment, nine participants performed five prolonged runs using commercial wearable devices. For each experiment, two segments were extracted from each trial from early and late in the run. For each participant, a random forest model was applied with a leave-one-run-out cross-validation to classify between the early (non-fatigued) and late (fatigued) segments. Additionally, group-based classifiers with a leave-one-subject-out cross validation were constructed. For experiment 1, mean classification accuracies for the single-subject and group-based classifiers were 68.2 ± 8.2% and 57.0 ± 8.9%, respectively. For experiment 2, mean classification accuracies for the single-subject and group-based classifiers were 68.9 ± 17.1% and 61.5 ± 11.7%, respectively. Variable importance rankings were consistent within participants, but these rankings differed from each participant to those of the group. Although the classification accuracies were relatively low, these findings highlight the advantage of subject-specific classifiers to detect changes in running biomechanics with fatigue and indicate the potential of using big data and wearable technology approaches in future research to determine possible connections between biomechanics and RRI.

The influence of midsole horizontal and vertical deformation on soft tissue vibrations and bone acceleration during running

Increased midsole deformation can limit exposure to high impact and vibration magnitudes while running. The aim of this study was to evaluate the effect of shoes eliciting different midsole deformation on ground reaction forces, heel impact, soft tissue vibrations and bone vibrations. Forty-eight runners performed a 5-min running task on an instrumented treadmill at a self-selected pace with four different shoes. Midsole horizontal and vertical deformations were quantified with relative displacement of seven reflective markers placed on the midsole of the shoe and tracked by eight optoelectronic cameras. Heel impacts, soft tissue and bone vibrations of lower leg muscle groups, sacrum and head were quantified with tri-axial accelerometers. Continuous wavelet transform was used to assess magnitude and frequency of the acceleration data. Linear mixed models and non-parametric one-dimensional regressions between the accelerometer data and shoe deformation were performed. Greater horizontal and vertical deformations decreased the magnitude (up to 4.6% per mm) and frequency (up to 0.6 Hz per mm) of soft tissue vibrations and bone accelerations. Accelerations of the heel, tibia, gastrocnemius medialis and vastus lateralis were more influenced than the sacrum and head. Increasing midsole deformation could therefore mitigate the risk of injury, while increasing running comfort and smoothness.