Tibial Accelerometry Is Not A Valid Assessment Of Internal Tibial Loads With Load Carriage

Tibial Accelerometry Is Not a Valid Assessment of Internal Tibial Loads during Walking and Running with Load Carriage PURPOSE: Tibial accelerations, via tibial-mounted inertial measurement units (IMUs), are proposed as surrogates for reference-standard, internal tibial bone loads during load carriage maneuvers. We assessed the relationship between metrics from an IMU and peak tibial bone load when walking and running with load carriage. METHODS: 34 fit participants (17 females. 24.7 ± 4.0 years, 6.0/10 ± 0.8 Tegner) with experience walking and running with torso-mounted loads. Participants walked (1.35 m/s) and ran (2.7 m/s) on an instrumented treadmill (1000-Hz) as 3-D marker data (200-Hz) and tibial accelerometry (IMU equipped with a tri-axial accelerometer ±16 g, 1000 Hz) were sampled. The following symmetrical loads were carried in a counterbalanced order: walking with 20.4 kg and 34.0 kg to replicate a fighting and approach load, respectively; running with 15.0 kg to replicate an armored plate carrier. A musculoskeletal model estimated axial tibial bone force from 3D motion data. Offsets due to gravity and signal drift were removed from the accelerometer signal. The resultant accelerations (i.e., root sum of squares of the three accelerometer axes) represented tibial shock. Associations of peaks of tibial shock and the vertical component of accelerometer signal (i.e., peak positive acceleration (PPA)), with peak tibial bone force were assessed via separate bi-variate correlations (α = 0.05). RESULTS: Nonsignificant associations with peak tibial bone force were found for peak tibial shock (walking: r = 0.06-0.28; p = 0.11-0.72; running: r = 0.33; p = 0.06) and PPA (walking: r = 0.04-0.23; p = 0.19-0.98; running: r = -0.15; p = 0.39). CONCLUSIONS: Peak tibial shock and PPA were not associated with peak tibial bone force during walking and running with load carriage, questioning the utility of IMUs in assessing tibial bone loads during load carriage training. - Mean (SD) for variables of interest. Pearson's r and associated p-values. Peak Tibial bone force (BWs) Peak tibial shock (g’s) Peak tibial shock vs. peak tibial bone force: Pearson’s correlation r (α-value) PPA (g’s) PPA vs. peak tibial bone force: Pearson’s correlation r (α-value) Walking (1.35 m/sec) Fighting load (20.4 kg) 5.1 (0.4) 3.9 (0.7) r = 0.28; p = 0.11 1.3 (0.3) r = -0.23; p = 0.19 Approach load (34.0 kg) 5.7 (0.4) 4.0 (0.7) r = 0.06; p = 0.72 1.3 (0.4) r = -0.04; p = 0.98 Running (2.7 m/sec) Simulated plate carrier (15.0 kg) 10.7 (1.3) 7.0 (2.3) r = 0.33; p = 0.06 5.2 (1.8) r = -0.15; p = 0.39 Supported by: AFRL FA8650-I9-C-612; UGP-18