Accordingly, as the speed of movement increases, the muscular contraction assumes more and more the nature of a twitch
(not in a strict physiological sense, for all voluntary movement is tetanic in character) or " whipped " effect and the relaxation that follows almost immediately, causes t he arm to travel as a relatively
frce body, given it s maximum imp et us at t he beginning of the movement .
We have here the explanation of the 1) Schleuder (slingshot) and 2) Wurf-Bewegungen (throwing movements) which played an important part in German piano pedagogy prior to 1920.
This effect of speed is noticeable in any movement the muscular contraction of which can be adequately observed.
It explains, for instance, why the
carpal extensors[1] cannot be felt to cont ract until the extension of the hand is done rap idly, or why t he flexors of the wrist contract only if the extension of t he fingers be rapid. When t hese movements are made slowly t he contraction may consume
more time, hence the need of maximal contraction is not present. The tendons therefore, will not 11 snap" into a taut
position and t heir contraction will not be noticeable. And besides, uuless the force required to move t he mass within the given time
be sufficiently great, these fore-arm muscles may not contract at all.
The mechanical need for such shifts in muscular reaction with variations in the force of movement is explained in the module
on Action and Reaction.
The effects we are here studying are speed effects, but variations in speed, so long as mass remains constant are variations in force.