The Effect of Running Speed on Cadence and Running Kinetics.

Background: Previous studies have shown that a lower running cadence (<170 steps/min) increases the risk of injury in runners. However, the immediate effect of increasing running speed on running cadence and ground reaction forces in experienced runners has not been well studied. Purpose/Hypothesis: The purpose of this study was to examine the immediate effect of running speed on running cadence and ground reaction forces in a sample of experienced runners. Study Design: Cross-sectional study. Methods: Thirty runners ages 21-49 (11 female, 19 male) consented to participate. Inclusion criteria included running at least 24 km (15 miles) per week for the past year, and no running-related injury in the prior three months. Subjects completed a 6-minute acclimatization to running on an instrumented treadmill, during which they identified their preferred training pace. After a short break, each runner then ran at seven predetermined speeds in the order as listed: 2.68 m/s, 2.82 m/s, 2.98 m/s, 3.35 m/s, 3.58 m/s, and 3.83 m/sec. Participants ran for 90 seconds at each of the speeds and during the final 30 seconds of each running bout, cadence was counted and ground reaction forces were recorded. Ground reaction forces measured included overall peak vertical force, vertical impact peak, vertical average loading rate, peak braking force, and braking impulse. Temporospatial and ground reaction forces were analyzed using repeated measures general linear model. Kinetic data from left and right limbs were compared using paired t-tests. Results: No significant differences existed between the right and left limb force data so only the left limb data are reported. Mean cadence increased from 169 steps/min at 2.68 m/s to 178 steps/min (p<0.001) at 3.83 m/s. All ground reaction force variables also increased significantly (p<0.001) from the slow to fast speed. Both stance time and step time decreased significantly (p<0.001) from the slow to the fast speed. Conclusions: The results of this study demonstrate that in a group of experienced runners, as running speed increases, both cadence and ground reaction forces increase. Concurrently, both stance time and step time decreased. Level of Evidence: Level 3.