Increasing step rate has been proposed to reduce overuse injury risk in runners by reducing the magnitude of musculoskeletal loading. Although estimating structure-specific loads is challenging, during level running, changes in a runner`s vertical ground reaction force (vGRF) may provide insight to changes in their musculoskeletal loading. Further, vGRF can be approximated using force sensing insoles. Purpose The primary goal of this study was to examine changes in peak insole force and cumulative weighted peak force (CWPF)/km with increased step rate in collegiate runners. The secondary goal was to determine whether sacral acceleration correlates with insole force when increasing step rate. Methods Twelve collegiate distance runners ran 1000 m outdoors at 3.83 m·s-1 at preferred and 10% increased step rates while insole force and sacral acceleration were recorded. Cumulative weighted peak force/km was calculated from insole force based on cumulative damage models. The effects of step rate on peak insole force and CWPF·km-1 were tested using paired t tests or Wilcoxon tests. Correlation coefficients between peak axial (approximately vertical) sacral acceleration times body mass and peak insole force were calculated on cohort and individual levels. Results Peak insole force and CWPF·km-1 decreased (P < 0.001) with increased step rate. Peak axial sacral acceleration did not correlate with peak insole force on the cohort level (r = 0.35, P = 0.109) but did within individuals (mean, r = 0.69-0.78; P < 0.05). Conclusions Increasing step rate may reduce peak vGRF and CWPF·km-1 in collegiate runners. Therefore, clinicians should consider step rate interventions to reduce peak and cumulative vGRF in this population. Individual-specific calibrations may be required to assess changes in peak vGRF in response to increasing step rate using wearable accelerometers.
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