Open-wheel race car driving: energy cost for pilots.

The aim of this study was to evaluate the energy cost of speedway open-wheel race car driving using actimetry. Eight pilot students participated in a training session consisting of 5 successive bouts of around 30 minutes driving at steady speed on the Bugatti speedway of Le Mans (France). Energy expenditure (EE, kcal) was determined continuously by the actimetric method using the standard equation. Energy cost was estimated through physical activity ratio (PAR = EE/BMR ratio, Mets) calculation after basal metabolism rate (BMR, kcal·min-1) estimation. A 1-met PAR value was attributed to the individual BMR of each volunteer. Bout durations and EE were not significantly different between driving bouts. Mean speed was 139.94 ± 2.96 km·h-1. Physical activity ratio values ranged 4.92 ± 0.50 to 5.43 ± 0.47 Mets, corresponding to a 5.27 ± 0.47-Mets mean PAR values and a 1.21 ± 0.41 kcal·min-1 mean BMR value. These results suggest that actimetry is a simple and efficient method for EE and PAR measurements in motor sports. However, further studies are needed in the future to accurately evaluate relationships between PAR and driving intensity or between PAR and race car type.

A virtual model of the bench press exercise.

The objective of this study was to design and validate a three degrees of freedom model in the sagittal plane for the bench press exercise. The mechanical model was based on rigid segments connected by revolute and prismatic pairs, which enabled a kinematic approach and global force estimation. The method requires only three simple measurements: (i) horizontal position of the hand (x(0)); (ii) vertical displacement of the barbell (Z) and (iii) elbow angle (theta). Eight adult male throwers performed maximal concentric bench press exercises against different masses. The kinematic results showed that the vertical displacement of each segment and the global centre of mass followed the vertical displacement of the lifted mass. Consequently, the vertical velocity and acceleration of the combined centre of mass and the lifted mass were identical. Finally, for each lifted mass, there were no practical differences between forces calculated from the bench press model and those simultaneously measured with a force platform. The error was lower than 2.5%. The validity of the mechanical method was also highlighted by a standard error of the estimate (SEE) ranging from 2.0 to 6.6N in absolute terms, a coefficient of variation (CV) < or =0.8%, and a correlation between the two scores > or =0.99 for all the lifts (p<0.001). The method described here, which is based on three simple parameters, allows accurate evaluation of the force developed by the upper limb muscles during bench press exercises in both field and laboratory conditions.

Offset of rotation centers creates a bias in isokinetics: a virtual model including stiffness or friction.

The present paper deals with a virtual model devoted to isokinetics and isometrics assessment of a human muscular group in the common joints, knee, ankle, hip, shoulder, cervical spine, etc. This virtual model with an analytical analysis followed by a numerical simulation is able to predict measurement errors of the joint torque due to offset of rotation centers between the body segment and the ergometer arm. As soon as offset is present, errors increase due to the influence of inertial effects, gravity effects, stiffness due to the limb strapping on the ergometer arm or Coulomb friction between limb and ergometer. The analytical model is written in terms of Lagrange formalism and the numerical model uses ADAMS software adapted to multi-body dynamics simulations. Results of models show a maximal relative error of 11%, for a 10% relative offset between the rotation centers. Inertial contributions are found to be negligible but gravity effects must be discussed in regard to the measured torque. Stiffness or friction effects may also increase the torque error; in particular when offset occurs, it is shown that errors due to friction have to be considered for all torque level while only stiffness effects have to be considered for torque less than 25Nm. This study also emphasizes the influence of the angular range of motion at a given angular position.