Human Force Exertion: The Significance of the Measure?

A basic research was conducted on a sample of twelve right-handed young males for pull actions of the upper limb on a gauge handle. The general purpose is to constitute an atlas of forces for french males, useful for ergonomics studies. Different conditions were tested before to select a standard protocol. Main difficulties concern the elimination of lower limbs contribution, the stability of the posture, the motivation of the subject and the choice of the parameters for the measure. Intra-individual variability in function of the protocols is in a range of 20-30%. With the usual standard protocol, this variability still remains if we try to evaluate maximal pull force during a week period. The interpretation of these data is not clear, and a more accurate definition of the measure is necessary before recommendations for normative data. Time duration of 5 seconds, real-time display of the force and maximal peak value seem to be an acceptable solution by comparison with a functional effort on a torque wrench that reflects a realistic action. It is proposed to use this procedure for the next experiments.

An assessment of the deflecting effect on human movement due to the Coriolis inertial forces in a space vehicle

Under conditions of prolonged space flight, it may be feasible to restore gravity artificially using centrifugal inertial forces in a spinning vehicle. As a result, the motion of the passengers relative to the vehicle is affected by Coriolis forces. The aim of this study is to propose a theoretical method to evaluate the extent of these effects compared to other inertial or motor forces affecting movement. We investigated typical right upper limb movement in a numerical model with a two-solid-links mechanism, including a spherical joint for the shoulder and a hinge joint for the elbow. The inertial and dimensional characteristics of this model derive from measurements and computations obtained on laboratory subjects. The same is true for the movements assigned to the model. These were inferred from actual recordings of arm movement when the subject presses a button placed in front of him with his index finger. From these relative velocities, the resulting forces and moments applied to the elbow and the shoulder were computed for a 1 rad s-1 rotational speed of transport motion, using classical kinetic relations. The result is that the Coriolis moments are of the same order of magnitude as the corresponding inertial moments and one-tenth of the value of a typical elbow flexion moment. Thus, they should cause a significant disturbance in movement.