From its inception, ergonomics was the study of the natural laws of work. Rohmert’s law describes one of those lawsalthough no one’s quite sure who Rohmert is. Simply put, the law states that the maximum force that an individual’s muscles can exert decreases exponentially from the time the exertion begins. Exponential decay is decrease at a rate proportional to its value, modeled by the equation N(t) N₀e(- ?t). Human factors and ergonomics researchers use this law to find the “maximum holding time” in a given situation.The force decays due to the way in which energy is supplied to the muscles. The human circulatory system continuously sends nutrients to muscles so that there is always a ready supply of energy. Any task requiring maximum force will use most of that energy all at once, which the circulatory system will then attempt to replenish. However, it cannot do so at a rate faster than that which the body is using. (more…)