Average vertical loading rate and tibial accelerometry are not valid assessments of internal tibial loads when...

Valid surrogates are needed to monitor tibial forces during tactical load carriage training. We assessed (a) effects of load carriage on internal tibial forces, average vertical loading rate (AVLR), and peak tibial accelerations; and (b) the relationships among these variables. Walking (1.35 m/s: 0-kg, 20.4-kg, and 34.0-kg) and running (2.7 m/s: 0-kg and 20.4-kg) biomechanics were sampled (n = 34). Peak tibial force increased with load carriage during walking and running (all p < 0.001; F:25.79-371.54). AVLR increased during walking with load carriage (p < 0.001; F = 131.83), with no difference (p = 0.61; F = 0.27) when running with load carriage. Peak tibial accelerations during walking increased with 20.4-kg of load carriage (p < 0.001-0.02). When load carriage was increased to 34.0-kg, small increases were observed for peak positive acceleration (+0.1 g, p = 0.02) only, with no change in peak resultant acceleration (p = 0.99). During running, peak tibial accelerometry surprisingly decreased (p = 0.01-0.04; F = 4.69-7.35) with load carriage. Peak tibial resultant accelerometry was only weakly to moderately associated with peak tibial force during running (r = 0.38-0.52; p = 0.002-0.04); with no other associations between peak tibial force, AVLR, and peak positive tibial acceleration (r = -0.23 - 0.13; p = 0.20-0.92). Thus, AVLR and tibial acceleration are questionable surrogates for internal tibial forces during walking or running, with or without load carriage.