What effect has the voluntary contraction of all the muscles of any member, each opposed set exerting the same degree of strength? No motion of the member results, but the member is brought on tension and stiffened. This is well illustrated in the case of the arm. Extend the arm and clench the fist; then contract all the muscles of the arm, about as the athlete does to display his muscular development. You will notice that the arm becomes stiff and tense. This state of tension is commonly called "muscular stiffness," but the term is open to objection. It is really the joints which are stiffened, not the muscles. We are, however, so accustomed to speak of muscular stiffness, and particularly of throat stiffness, that little is to be gained by substituting a more accurate expression. A condition of muscular stiffness results from the contraction of all the muscles of a member, whether this contraction be voluntary or involuntary. This condition does not prevent the normal movements of the member; it only renders the movements more difficult and fatiguing and less effective. It is readily seen why this is the case. More than the necessary strength is exerted by the muscles. Suppose the biceps and triceps, for example, each to be contracted with five units of strength; then let some work be performed by the flexing of the forearm, requiring the exertion of two units of strength. In this case the biceps must exert two units of strength more than the triceps, that is, seven units. In all, the two muscles together exert twelve units of strength to accomplish the effective result of two units. Six times the needed strength is exerted. Activity of this kind is naturally fatiguing. Muscular stiffness increases the difficulty of complex movements. Not only is unnecessary strength exerted; the stiffness of the joints also interferes with the freedom and facility of motion. But this unfavorable condition does not upset the power of coordination. The instinctive connection between the nerve centers of consciousness and the motor centers is not broken. Although hampered in their efforts, the muscles are still able to execute the demands of consciousness. As an illustration of this analysis of muscular stiffness let us consider the actions of writing, when performed under the conditions just described. It is possible to write with the hand and arm in a state of muscular stiffness. But one does not write so easily, so rapidly, nor so well with the arm stiff as with the arm normally relaxed. Closer attention must be paid to the forming of the letters, and more effort must be put forth to write with the muscles stiffened; yet the result is not equal to that obtained with less care and labor under normal muscular conditions.