Passage Four

Design of all the new tools and implements is based on careful experiments with electronic instruments. First, a human "guinea pig" is tested using a regular tool. Measurements are taken of the amount Of work done, and the buildup of heat in the body. Twisted joints and stretched muscles can not perform as well, it has been found, as joints and muscles in their normal positions. The same person is then tested again, using a tool designed according to the suggestions made by Dr. Tichauer. All these tests have shown the great improvement of the new designs over the old. One of the electronic instruments used by Dr. Tichauer, the myograph (肌动记器), makes visible through electrical signals the work done by human muscle. Another machine measures any erous features of tools, thus proving information upon which to base a new design. One conclusion of tests made with this machine is that a tripod (三脚架) stepladder is more stable and safer to use than one with four legs. This work has attracted the attention of efficiency experts and time-and-motion-study engineer, but its value goes far beyond that. Dr. Tichauer’s first thought is for the health of the tool user. With the repeated use of the same tool all day long on production lines and in other jobs, even light manual work can put a heavy stress on one small area of the body. In time, such stress can cause a disabling disease. Furthermore, muscle fatigue is a serious safety hazard. Efficiency is the by-product of comfort, Dr. Tichauer believes, and his new designs for traditional tools have proved his point.

From the passage we know that joints and muscles perform best when ______ .