In traditional standards, rules, and safety regulations environmental stress is assessed by connecting intensity and duration by means of a multiplication, i.e., a mutual settlement of high workload and short duration and a lower intensity exposed for a correspondingly longer duration. This principle is based on the hypothesis that equal energy or dose – also known for dynamic muscle work as the principle of equal work – involves equal human related effects. But such guidelines are more closely related to physics than to physiology. Yet, ergonomics and occupational medicine have to concern themselves not only with physics but principally with physiological cost as well as short-term and long-term effects on humans in the domain of strain. Experimental data from laboratory studies in noise elucidate that physiological cost is not congruent with the principle of equal energy. 10 subjects between the ages of 23 and 43 participated in a cross-over trial laboratory study. They were exposed to 94 dB(A) for 1 h, 113 dB(A) for 45 s, and impulsive noise with a mean level of 113 dB(A) for 250, 100, 25, and 5 ms. The 6 noise situations were all energy equivalent to 85 dB(A) / 8 h. Temporary hearing threshold shift and its recovery was measured at 4 and 6 kHz, respectively. A shorter exposure duration and a corresponding increase in noise level lead to a significant decrease in the TTS₂ as well as in the restitution time. Yet, the fractionation of continuous noise at 113 dB(A) for 45 s into an energy equivalent number of impulses – which lasted only 5 ms in the end – was associated with a considerable and highly significant increase in the TTS₂ and in the required restitution time up to 10 hours. Finally, the integrated restitution temporary threshold shift (IRTTS), representing overall physiological cost, revealed a risk for 5-ms impulses that is 2.5 times higher than that of 94 dB(A) / 1 h or 85 dB(A) / 8 h.