Effects of speed, load, and surface on tibial bending moment and stress

This study assessed locomotor speed, body-borne load, and surface on tibial stress and bending. Fourteen recreational runners had tibial bending moments quantified during a jog (3.0 m/s) and run (4.5 m/s) over a flat and uneven surface with and without 15 kg body-borne load. Peak and mean values of AP, ML and resultant tibial stress and bending moments were quantified and submitted to 3-way repeated-measures ANOVA, while stress and bending waveforms were submitted to statistical parametric mapping 3-way ANOVA. During the run, mean and peak AP and resultant tibial bending moments and stress increased (all: p ≤ 0.009), while all stress and bending waveforms were larger from 0 to 11% and 70 to 100% of stance (all: p ≤ 0.031). With the 15 kg load, mean and peak AP and resultant tibial bending moments and stresses increased (all: p ≤ 0.008) and greater waveform from 13 to 36% and 95 to 100% of stance was exhibited for all bending moment and stresses (all: p ≤ 0.043). On the uneven surface, participants decreased mean and peak AP and resultant tibial bending moments and stresses (all: p ≤ 0.010) and used smaller tibial stress and bending waveforms between 0 to 13%, 18 to 20%, and 69 to 86% of stance for all moments and stresses (all: p ≤ 0.033). Faster run speed and heavier load may elevate risk of tibial stress fracture, while traversing an irregular, uneven surface led to significant reduction in tibial stress and may not similarly elevate injury risk.