Georges Poumarat

Comparison of mechanical properties of human, bovine bone and a new processed bone xenograft

The study compared the mechanical properties of human bone, fresh bovine bone and a new highly purified bone xenograft: T650 (Lubboc-Laddec). Destructive, compressive tests were performed to determine Youngs modulus and ultimate strength, with a constant deformation rate of 0.025 mm min-1. The stress-strain curves obtained from all the non-human specimens especially the T650, did not differ significantly from those observed with human bone. Human and fresh bovine samples presented a significantly different Youngs modulus. The T650 samples, depending upon their trabecular texture (dense or medium) also differed significantly from each other (132.9 +/- 52.3 versus 80.0 +/- 37.3 MPa, P < 0.05). Their moduli were similar to those of bovine and human cancellous bone, respectively (117.49 +/- 61.53 versus 77.36 +/- 54.96. P < 0.05). The ultimate strength of T650 dense (9.6 +/- 3.7 MPa) was similar to bovine (8.5 +/- 4.2 MPa) and human bone (8.78 +/- 5.2 MPa): the T650 medium (5.9 +/- 2.8 MPa) was significantly different from the other specimens.

Task-involvement and ego-involvement goals during actual and imagined movements : Their effects on cognitions and vegetative responses

It has been experimentally proven many times that the mental rehearsal of an activity not only improves motor performance but also has vegetative effects whose magnitude is correlated with the amount of imagined effort. These beneficial effects of mental imagery have been explained in terms of central programming structures capable of anticipating the metabolic demands of the task. Twenty-four subjects were asked to actually perform and also imagine an isometric contraction of the forearm under various goal conditions: a task-involving goal (8 subjects), an ego-involving goal (8 subjects), and no goal (8 subjects). During the contractions, electromyographic potential and heart rate were measured. Afterwards, the subjects were asked to indicate the amount of effort expended under different feedback conditions. The results showed no trace of electromyographic activity during the imagined contractions when the lack of movement was controlled using a force sensor. On the other hand, a significantly faster in heart rate was observed with a task- or ego-involving goal than with no goal, during both actual and imagined contraction. Similarly, as predicted, subjects said they applied less effort in the positive feedback condition, and more effort in the negative feedback condition with an ego-involving goal. The results are discussed in the light of goal theories, while regarding goals not only as serving to anticipate metabolic expenditures but also as promoting a self-image of competence, particularly in threatening, ego-involving situations.