An extreme example of this form of nervousness is offered by the unfortunate sufferer from stage fright. In this condition the entire body often stiffens, and purposeful movement of any kind becomes for a time impossible.
(c) Contractions caused by Special Attention to Certain Members
Suppose a small boy of sensitive nature to enter a room suddenly, and to be at once chided for his awkwardness. His body will probably stiffen, and his awkwardness become more pronounced. Now call his attention to his hands and tell him he is holding them badly. His arms and hands will immediately become painfully stiff. Speak of his feet and his legs come on tension. Whatever member his attention is turned to, the muscles of that part contract involuntarily.
Photographers sometimes have to contend with this form of involuntary action on the part of their sitters. When the hands are to be posed the arms stiffen; so also do the legs, the shoulders, and the neck, each when its turn comes to receive attention.
Under normal conditions this form of awkwardness is easily overcome. Sitting for a photograph soon becomes a simple matter. The boy outgrows the awkward stage and gradually acquires a natural and easy bearing. Muscular stiffening due to attention to special members is usually the result of an uncomfortable feeling of being out of one's element, and ill at ease in one's surroundings. So soon as this feeling wears off the tendency to this form of stiffness disappears.
(d) Contractions of Muscles due to the Radiation of Nerve Impulse
A voluntary exertion of some of the muscles of a member sometimes causes the involuntary contraction of all the other muscles of the part. As will readily be seen, the exercise then takes place under conditions of muscular stiffness. This is commonly a feature of the unskilful and unaccustomed performance of muscular activities. A few examples will serve to illustrate this type of involuntary contraction better than a lengthy discussion of the physio-psychological principles involved.
When a novice takes his first lesson in riding a bicycle he clutches the handle bars in a vise-like grip. His knees are so stiff as to bend only with a great exertion of strength. To steer the wheel the learner must put forth his most powerful muscular efforts. A half-hour lesson in bicycle riding often tires the beginner more than an afternoon's ride does the experienced cyclist.
This condition of muscular stiffness is due to the contraction of antagonist groups of muscles, involving practically the entire body. In one sense the excessive muscular contractions are involuntary; yet it would not be easy to define where the voluntary element of the contractions leaves off.
A similar excessive expenditure of strength may be seen in the attempt of an illiterate laborer to sign his name. He grips the pen as though it were a crowbar, and puts forth enough strength to handle a twenty-pound weight. Learning to dance, or to skate, or to row a boat, is usually accompanied in the beginning by this form of muscular stiffness.