Measured and predicted mechanical internal work in human locomotion Francesca Nardello a,⇑ , Luca P. Ardigò a , Alberto E. Minetti b a Faculty of Exercise and Sport Science, Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, Italy b Faculty of Medicine, Department of Human Physiology, University of Milano, Italy article info Article history: Available online 5 November 2010 PsycINFO classification: 2220 2260 Keywords: Human locomotion Mechanical internal work Model equation Velocity Gradient abstract 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 previ- ously proposed model equation predicts such a parameter based upon velocity, stride frequency, duty factor, and a compound crit- ical 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. Ó 2010 Elsevier B.V. All rights reserved. 0167-9457/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.humov.2010.05.012 ⇑ Corresponding author. Address: Faculty of Exercise and Sport Science, University of Verona, Via Felice Casorati, 43, 37131 Verona, Italy. Tel.: +39 045 8425139; fax: +39 045 8425131. E-mail address: narfra@yahoo.it (F. Nardello). Human Movement Science 30 (2011) 90–104 Contents lists available at ScienceDirect Human Movement Science journal homepage: www.elsevier.com/locate/humov