Step Rate Retraining to Reduce Injury and Disability: A Randomized Controlled Trial

Volunteers meeting all inclusion and exclusion criteria will read and sign an informed consent form approved by the institutional review board (IRB). After consenting, each participant will answer a demographic questionnaire related to injury history and pertinent injury risk factors (location, duration and type of previous injury, profile time, height, weight, changes in menstruation, etc). The participant will then undergo a running analysis in which the individual will run on an instrumented treadmill while video of running form in the sagittal plane and frontal plane are captured using two stationary two-dimensional digital cameras sampling at 240 Hz. The video will capture the runner from the waist down in order to protect privacy and blinding. Information collected from the treadmill will include AVLR of vGRF, while step rate and other kinematic information will be collected from video analysis. Volunteers will run at their self-selected pace for three minutes on a treadmill, with step rate and AVLR analyzed during the last minute of running. During the inital data collection, if the participant's step rate is greater than 176 spm, the participant will be exluded from the study at this time. The same data collection procedure will be repeated for all participants after retraining and for a subset of participants at 6 months to observe post intervention AVLR and step rate.

Volunteers will then be placed into a retraining group and a control group through random allocation. Each participant, regardless of group, will be provided a Garmin Forerunner35 to use while performing PRT with their unit and/or personal physical training for ten in-field training sessions. The ten in-field training sessions will be performed by the participant outside of the researcher's lab without a researcher present. The participant will be instructed to return to their normal running routine, but to use the watch during 10 running sessions to either monitor and modify their step rate for the retraining group or their pace and distance for the control group. Both groups will receive a training log to track their training sessions.

The retraining group will receive a watch accelerometer to use for monitoring their step rate with instructions to increase their preferred step rate by 7.5% over the ten in-field training sessions. The runner will receive a training log with a target step rate recorded on it. The target step rate will be a 7.5% increase from the preferred step rate the runner used during the gait analysis. The researcher will provide instruction to the participant to match the target step rate while the participants are performing their in-field training sessions by using the watch to monitor their step rate. The watch provides the runner with real-time feedback on their step rate. This allows the runner to monitor their step rate while running and the runner should either increase or decrease their step rate to meet the target step rate provided by the study team member. Training units at FT. Sam Houston perform ability group or self-paced runs for the majority of their endurance training, so participants should not have difficulty adjusting their step rates IAW study plans. Willy et al. was successful using eight in-field training sessions to sustain a 7.5% increase in step rate 1 month post-training in healthy runners (Willy 2016). Adherence to step rate will be assessed at the follow-up by reviewing the last 7 training sessions in the history of the watch. The watch only saves 7 sessions at a time to the watch memory without connecting to an internet database. Viewing the last 7 sessions allows the investigators to assess adherence without relying on the runner to upload data to a server before the participants have completed their training sessions. The average step rate from the last 7 training sessions will be input into an excel spreadsheet and the training sessions will be deleted from the watch.

The control group will receive the same device to monitor their pace but receive no instruction to change their preferred step rate. The participant will also receive a training log, but will track their pace and distance for each run.

Every participant will perform a 2-3 minute running session on the treadmill after data collection in order to acclimate looking down at the watch, periodically, for 3-5 seconds. This should minimize risk with falling while intermittently looking at the watch for feedback while running overground without supervision.