Accelerometer-equipped Running Watch Provides A Valid Estimate Of Peak And Cumulative Weighted Peak Force

PURPOSE: We validated an algorithm and a commercial chest-mounted accelerometer to estimate vertical ground reaction force (vGRF) and cumulative bone damage during running. METHODS:Derivation stage: 18 well-trained runners (9 males/9 females: 26.0 yrs ± 4.4; 70.2 kg ±10.8; routine training pace = 3.3 m/sec ±0.3) ran 60-sec conditions (2.7, 3.0, 3.3, 3.6, 4.0 m/sec and routine training pace) as data were sampled via an instrumented treadmill (gold standard) and the accelerometer. A sine-wave model used flight time, contact time, and step frequency from the accelerometer to estimate peak vGRF and cumulative peak vGRF/km. A regression-based algorithm was then derived to adjust for the sine-wave model’s systematic underestimation of peak vGRF. Validation stage: Next, the derived algorithm was validated using the same procedures in an independent sample of 7 well-trained runners, to date (3 males/4 females: 24.3 yrs ± 1.0; 73.2 kg ±9.6, routine training pace =3.2 m/sec ±0.3). Proof-of-concept: To illustrate how these methods can be applied to runners at risk for a bone stress injury, cumulative bone damage/ km (i.e., Palmgren-Miner rule) was estimated by raising vGRF by a power of 6.6 to yield cumulative weighted peak force/km. Criterion validity was assessed via linear regressions (α = 0.05) and absolute and percent mean bias error. RESULTS: The derivation stage yielded excellent relationships (r2 = 0.81-0.87; p < 0.001), but large mean error biases for vGRF and cumulative damage estimates from the accelerometer versus the gold standard. The validation stage yielded excellent relationships with mean bias errors <1% between the accelerometer and the gold standard for all metrics. CONCLUSIONS: A commercially available accelerometer and the derived algorithm produced valid estimates of vGRF and cumulative bone damage. The proof-of-concept analysis suggests these methods may have utility in monitoring training loads in runners at-risk for bone stress injury. - Gold standard Accelerometer r 2 p-value Absolute Mean Bias Error Percent Mean Bias Error Derivation stage (n = 18) Stance duration (ms) 242.0 (±0.28) 238.9 (±0.24) r2 = 0.84 p < 0.001 -3.0 -1.2% Flight time (ms) 105.4 (±0.27) 108.4 (±0.23) r2 = 0.82 p < 0.001 3.1 2.9% Peak vGRF (BW) 2.52 (±0.27) 2.30 (±0.22) r2 = 0.87 p < 0.001 -0.28 -11.1% Cumulative peak vGRF/km (BW/km) 1090.0 (±131.9) 994.1 (±109.2) r2 = 0.85 p < 0.001 -95.9 -8.8% Cumulative weighted peak force/km (105 BW6.6/km) 11.41 (±1.53) 10.11 (±1.17) r2 = 0.81 p < 0.001 -1.30 -11.4% Validation stage (n = 7) Peak vGRF (BW) 2.55 (±0.19) 2.54 (±0.15) r2 = 0.83 p < 0.001 -0.01 -0.4% Cumulative peak vGRF /km (BW/km) 1050.0 (±91.1) 1048.3 (±104.8) r2 = 0.90 p < 0.001 1.26 -0.1% Cumulative weighted peak force/km (105 BW6.6/km) 11.46 (±0.99) 11..41 (±0.81) r2 = 0.77 p < 0.001 0.047 -0.4%