Effects of a Submaximal 30-Minute Run on Peak Tibial Acceleration in Novice Runners

Abstract

Peak positive tibial acceleration (PTA) immediately following foot strike during running is greater in runners with a history of tibial stress fracture. PTA does not increase over the course of a 20min run at lactate threshold pace (i.e., moderate effort) in highly trained runners. However, injury incidence in novice runners is higher, which may suggest that novice runners do not have the control strategy to prevent PTA from increasing over a prolonged run. PURPOSE: To assess the effects of a prolonged submaximal run on PTA in novice runners. METHODS: Male (n = 2) and female (n = 8) novice runners (24±5yrs; 1.69±0.12m; 70.7±15.6kg; 24.5±3.8kg/m2) who had been training for less than two years and ran on average at least 16km per week completed a 30min treadmill run at a self-selected speed equivalent to a rate of perceived exertion using the Borg scale between 10-13. A 3D accelerometer (480Hz, PCB Piezotronics, USA) used to measure PTA immediately following foot strike was attached to the distal anteromedial aspect of the right tibia along its longitudinal axis. Sagittal plane foot contact angle and ankle angle were also computed using 3D motion capture data (240Hz, Qualisys, Sweden). Data from five consecutive steps were collected after four (start), 15 (middle) and 30 min (end) of the prolonged run. A one-way repeated measures ANOVA was used assess a main effect of time on PTA (p ≤ 0.05). Post-hoc paired t-tests were used to compare mean differences among time points. Cohen’s d effect sizes were used to assess effect magnitudes. RESULTS: PTA was not different among time points (p = 0.87). PTA was unchanged between time points during the prolonged run (start: 3.58±1.43g; middle: 3.67±1.09g; end: 3.60±1.47g). Both foot contact angle and ankle angle at foot strike were unaffected by the run (p > 0.05). CONCLUSION: Our data suggest that PTA does not change over the course of submaximal prolonged run in novice runners. This finding is similar to unchanged PTA during a 20min moderately intense run in trained runners. These findings appear to indicate that, independent of running experience, PTA is unaffected by prolonged running. Changes in lower extremity motion and stiffness over prolonged runs of different lengths and intensities may alter active shock attenuation mechanisms and have different impacts on PTA on novice runners.