Measured and predicted mechanical internal work in human locomotion

Predictive methods estimating mechanical internal work (W_int, i.e., work to accelerate limbs with respect to BCOM during locomotion) are needed in absence of experimental measurements. A previously proposed model equation predicts such a parameter based upon velocity, stride frequency, duty factor, and a compound critical term (q) accounting for limb geometry and inertial properties. That first predicted W_int estimate (PW_int) has been validated only for young males and for a limited number of horses. The present study aimed to extend the comparison between model predictions and experimentally measured W_int (MW_int) data on humans with varying gender, age, gait, velocity, and gradient. Seventy healthy subjects (males and females; 7 age groups: 6-65 years) carried out level walking and running on treadmill, at different velocities. Moreover, one of the subject groups (25-35 years) walked and ran also at several uphill/downhill gradients. Reference values of q represent the main important results: (a) males and females have similar q values; (b) q is independent on velocity and gradient. Also, different data filtering depth was found to affect MW_int and, indirectly, PW_int, thus also the reference q values here obtained (0.08 in level, 0.10 in gradient) suffer a - 20% underestimation with respect to the previous predicting model. Despite of this effect, the close match between MW_int and PW_int trends indicates that the model equation could be satisfactorily applied, in various locomotion conditions.