Fast Running Does Not Contribute More to Cumulative Load than Slow Running

Purpose As running speed increases there are concomitant changes in loads associated with tibial stress fracture risk. Runners often include multiple speeds in their training, but the effect of speed distribution on load accumulation is unknown. We studied how running at different proportions of speed within a given running distance affects the cumulative loading of the vertical average loading rate, cumulative peak absolute tibial free moment, and cumulative peak axial tibial load. These loads were compared between two proportions of speed: running all distance at normal self-selected speed, and running the same distance at a combination of slow/fast speeds with the same average speed as normal. Also, the contributions of slow and fast running to the combined condition were compared. Methods 43 recreational runners (age 18-49y, 29 female, 14 male) ran around a 50-m indoor track for three laps each at self-selected slow, normal, and fast speeds. Per-step peak loads and cumulative loads per kilometer were calculated at each speed and for each speed distribution, respectively. Results Only cumulative vertical average loading rate was lower at normal speed compared to the slow/fast speed combination. The contribution of fast speed running to cumulative tibial load was less than the contribution of slow speed running. Conclusion Running at a combination of slow and fast speeds, rather than a single moderate speed, increased cumulative vertical average loading rate but not cumulative tibial load or free moment. Fast running can be included in a training program without necessarily increasing the cumulative load. Total distance and average speed may not be sufficient information to estimate cumulative load from running training. Corresponding author: Jessica G. Hunter, 4200 Valley Drive, University of Maryland, College Park, MD, USA 20742. Phone: 786.218.6022. Email: jghunter@umd.edu This study was supported by a grant from Maryland Technology Enterprises Institute. Conflict of interest: The authors have no conflicts of interest. The results of this study do not constitute endorsement by the ACSM. The results of this study are presented clearly and honestly without fabrication, falsification, or inappropriate data manipulation. Accepted for publication: 3 January 2019. © 2019 American College of Sports Medicine

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