Relationships between Habitual Cadence, Footstrike, and Vertical Load Rates in Runners

Excessive vertical ground reaction force (VGRF) load rates have been linked with running injuries. Increasing cadence (CAD) has been shown to reduce load rates; however, relationships between habitual cadence and load rates across a population of runners have not been examined. Purpose To examine the relationships between habitual running cadence and vertical load rates in healthy and injured runners using habitual footstrike patterns. As CAD increased, we expected vertical load rates would decrease. Methods Healthy runners (n = 32, 25 men) and injured runners (n = 93, 45 men) seeking treatment were analyzed. Footstrike classifications were heel at initial contact (rearfoot strike [RFS]) or forefoot at initial contact (forefoot strike [FFS]). Runners were divided into four injury status/footstrike pattern (FSP) subgroups: healthy RFS (n = 19), injured RFS (n = 70), healthy FFS (n = 13), and injured FFS (n = 23). The VGRF and CAD were recorded as participants ran on an instrumented treadmill at self-selected speed (x<overbar> = 2.6 ms(-1) 0.12). Healthy runners used laboratory footwear similar to their habitual footwear, and injured runners used habitual footwear. The vertical average load rates and vertical instantaneous load rates of the VGRF of each runner's right leg were calculated and correlated with CAD for four injury status-FSP subgroups and for all runners combined. Results There were no differences in CAD between all runners or any subgroup (P > 0.05). Vertical average load rates and vertical instantaneous load rates were significantly higher (P 0.01) in the injured RFS group compared with all other subgroups. Injured FFS and healthy FFS had similar load rates (P = 1.0). Conclusions We found no relationships between habitual running cadence and vertical load rates. The highest load rates were in injured RFS runners, and the lowest load rates were in FFS runners, regardless of injury status. Future studies of gait retraining to increase CAD and reduce load rates should follow runners long term to examine this relationship once CAD has become habituated.