Between-session reliability and minimal detectable difference of peak tibial acceleration during running on an indoor track

Peak tibial acceleration (PTA) is commonly used to assess impact loading during running, but the number of strides required for reliable between-session measurement in overground conditions, as well as the minimal detectable difference (MDD), remains unclear. This study evaluated the one-week and three-week reliability of axial and resultant PTA during overground running and determined the minimum number of strides needed for good and excellent reliability. Eleven recreational runners completed three sessions on a 200-m indoor oval track while wearing a tibial-mounted accelerometer. PTA was analysed across different stride intervals, and test-retest reliability was assessed using intraclass correlation coefficients (ICC). Results showed moderate-to-good reliability for axial PTA (ICC = 0.71-0.80 at 1 week, 0.67-0.84 at 3 weeks) and moderate-to-excellent reliability for resultant PTA (ICC = 0.81-0.94 at 1 week, 0.78-0.91 at 3 weeks). Based on our results, we recommend averaging at least 40 strides to achieve good reliability for axial PTA (MDD = 2.93 g), and at least 100 strides to achieve excellent reliability of resultant PTA (MDD = 2.72 g). These findings support the reliability of PTA when evaluating longer-term interventions, such as gait retraining, but researchers should consider stride variability and track curvature when interpreting results.