Purpose Recent observations demonstrate that a sizeable proportion of the recreational running population runs at rather slow speeds and does not always show a clear flight phase. This study determined the key biomechanical and physiological characteristics of this running pattern, i.e., grounded running (GR), and compared these characteristics with slow aerial running (SAR) and reference data on walking at the same slow running speed. Methods Thirty male subjects performed instructed GR and SAR at 2.10 m·s−1 on a treadmill. Ground reaction forces, tibial accelerations, and metabolic rate were measured to estimate general musculoskeletal loading (external power and maximal vertical ground reaction force), impact intensity (vertical instantaneous loading rate and tibial acceleration), and energy expenditure. More explicit measures of muscular loading (muscle stresses and peak eccentric power) were calculated based on a representative subsample, in which detailed kinematics and kinetics were recorded. We hypothesized that all measures would be lower for the GR condition. Results Subjects successfully altered their running pattern upon a simple instruction toward a GR pattern by increasing their duty factor from 41.5% to 51.2%. As hypothesized, impact intensity, general measures for musculoskeletal, and the more explicit measures for muscular loading decreased by up to 35.0%, 20.3%, and 34.0%, respectively, compared with SAR. Contrary to our hypothesis, metabolic rate showed an increase of 4.8%. Conclusions Changing running style from SAR to GR reduces musculoskeletal loading without lowering the metabolic energy requirements. As such, GR might be beneficial for most runners as it has the potential to reduce the risk of running-related injuries while remaining a moderate to vigorous form of physical activity, contributing to fulfillment of the recommendations concerning physical activity and public health.

ObjectivesRecreational runners show a large interindividual variation in spatiotemporal characteristics. This research focused on slow runners and intended: (1) to document the variance in duty factor (DF) between runners in a real-life running setting and (2) examine whether the interindividual variation in DF and stride frequency (SF) relates to differences in external loading parameters between runners.MethodsSpatiotemporal characteristics of 23 slow runners (ie, <2.6 m/s) were determined during a 5.2 km running event. To relate the interindividual variation in DF and SF to differences in external forces between runners (maximal vertical ground reaction force (FzMax), peak braking force (PBF) and vertical instantaneous loading rate (VILR)), 14 of them were invited to the lab. They ran at 1.9 m/s on a treadmill while ground reaction forces were recorded. A multiple linear regression analysis was conducted to investigate the effect of DF and SF on external force measures.ResultsDF between slow runners varied from 42.50% to 56.49% in a recreational running event. DF was found to be a significant predictor of FzMax (R²=0.755) and PBF (R²=0.430). SF only improved the model for PBF, but to a smaller extent than DF (R² change=0.191). For VILR, neither DF nor SF were significant predictors.ConclusionExternal forces are lower in recreational runners that run with higher DFs and slightly lower SFs. These findings may be important for injury prevention purposes, especially directed to recreational runners that are more prone to overuse injuries.

Purpose The present study aimed to determine whether runners can reduce impact measures after a six‐session in‐the‐field gait retraining program with real‐time musical biofeedback on axial peak tibial acceleration (PTAa) and identify the associated biomechanical adaptations. Methods Twenty trained high‐impact runners were assigned to either the biofeedback or the music‐only condition. The biofeedback group received real‐time feedback on the PTAa during the gait retraining program, whereas the music‐only condition received a sham treatment. Three‐dimensional gait analysis was conducted in the laboratory before (PRE) and within one week after completing the gait retraining program (POST). Subjects were instructed to replicate the running style from the last gait retraining session without receiving feedback while running overground at a constant speed of 2.9 m∙s−1. Results Only the biofeedback group showed significant reductions in both PTAa (∆x̅ = −26.9%, p = 0.006) and vertical instantaneous loading rate (∆x̅ = −29.2%, p = 0.003) from PRE to POST. In terms of biomechanical adaptations, two strategies were identified. Two subjects transitioned toward a more forefoot strike. The remaining eight subjects used a pronounced rearfoot strike and posteriorly inclined shank at initial contact combined with less knee extension at toe‐off while reducing vertical excursion of the center of mass. Conclusions After completing a music‐based biofeedback gait retraining program, runners can reduce impact while running overground in a laboratory. We identified two distinct self‐selected strategies used by the participants to achieve reductions in impact.

PurposeRunning with increased duty factors (DF) has been shown to effectively reduce external forces during running. In this study, we investigated whether running with increased DF (INCR) also reduces internal musculoskeletal loading measures, defined as peak muscle forces, muscle force impulses, and peak joint contact forces compared with a runners’ preferred running pattern (PREF).MethodTen subjects were instructed to run with increased DF at 2.1 m·s−1. Ground reaction forces and three-dimensional kinematics were simultaneously measured. A musculoskeletal model was used to estimate muscle forces based on a dynamic optimization approach, which in turn were used to calculate muscle force impulses and (resultant and three-dimensional) joint contact forces of the ankle, knee, and hip joint during stance.ResultsRunners successfully increased their DF from 40.6% to 49.2% on average. This reduced peak muscle forces of muscles that contribute to support during running, i.e., the ankle plantar flexors (−19%), knee extensors (−18%), and hip extensors (−15%). As a consequence, peak joint contact forces of the ankle, knee, and hip joint reduced in the INCR condition. However, several hip flexors generated higher peak muscle forces near the end of stance.ConclusionsRunning with increased DF lowers internal loading measures related to support during stance. Although some swing-related muscles generated higher forces near the end of stance, running with increased DF can be considered as a preventive strategy to reduce the occurrence of running-related injuries, especially in running populations that are prone to overuse injuries.

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