Contraction facial isotonic muscle. Whole Muscle Contraction Did you know that your muscles are contracting even when you're trying to rest? Changes in force and stiffness during fatigue of frog isolated muscle fibres. Let's re-examine our weight lifter. J Appl Physiol While he's looking away, a mischievous friend replaces the 25 kilogram weight with a 50 kilogram weight. The masseter corresponds to one of the muscles of mastication. How Muscular Contraction Causes Articulation: Guanabara, Rio de Janeiro, pp.