Background: Injury rates among triathletes have been reported to be as high as 87%. Previous research has established that some triathletes display altered kinematics during running after cycling, compared to an isolated run. These kinematic changes include increased anterior pelvic tilt, decreased hip extension, and increased variability in stride length and time. The purpose of this study was to determine whether a hip flexor stretch performed in the brief transition period between cycling and running would result in a post-cycling (transition) run more similar to a control run.

Methods: Twelve participants performed a 5-minute baseline run, a 15-minute transition run with no intervention, and a 15-minute transition run with a bilateral hip flexor stretch between the cycling and running periods. Kinematic data were collected with a Vicon motion capture system. Segment angles, joint angles and stride lengths were calculated at a single time point in the baseline run and at 3 time points in each of the transition runs.

Results: Peak forward trunk lean, peak anterior pelvic tilt, peak hip extension, and peak hip flexion were significantly dependent upon run condition. Trunk lean and pelvic tilt significantly increased at all time points in both the no-stretch and stretch transition runs compared to baseline. Hip extension increased in the first minute of the stretch transition run, while hip flexion decreased in the first minute of the no-stretch transition run and in the 1 and 5-minute time points in the stretch transition run compared to baseline. Forward trunk lean and anterior pelvic tilt were lower in the stretch transition run before the 10-minute time point compared to the no-stretch transition run, though these differences were not significant.

Conclusion: An intervening hip flexor stretch provided only a modest and non-significant improvement in anterior pelvic tilt and forward trunk lean in the early stages of post-cycling running. The sustained increases in anterior pelvic tilt and trunk lean suggest that hip flexor tightness is not the only factor driving kinematic changes during transition running. Further investigation is needed to determine the mechanisms of cycling’s effects on running biomechanics.