Jan 11, 2002
Q: what is the sole effect of muscle hyper/hypo-trophy (or force change) on the mechanical power generated across the joint (i.e. when the shortening of the muscle is kept constant)?
A: the simple answer is that power increases with the force change to the power of 1.5 (power is force times velocity, thus is force increases, also speed increases, and the product of the two is potentiated beyond the simple force change). I wrote a mathematical model that tells us that the gain in power depends also on whether the movement is horizontal or vertical.
Two linear actuators launching a ball serve as a metaphor for the comparison between two muscles of different force (or cross-sectional area) acting maximally over the same distance and against the same load. The illustrated simulations, obtained by using Working Model 2D (Knowledge Revolution, USA) to test the predictions of the mathematical model, anticipates some of the results from the present paper. The left panel shows the vertical extension, where gravity contrast the motion, while the right one refers to an horizontal extension (in this case, the actuators are represented as seen from above). While in both cases the strength of the red actuator (labelled with a '2' in the equations) is threefold with respect to the blue one (labelled with a '1'), the gain in power is very different. As shown in the text, this is due to the fraction of the actuator force devoted to vertically contrast the load (ball) during the extension.
Fpost/Fpre
