[Modern labor and stress on skeletal muscles]

Introductorily the actual state in analysis and evaluation of physical work is characterized as a problem of changing chemical into mechanical energy in the skeletal muscle. Modern work is characterized in the view of the physiologist. Considering experimental results and epidemiological studies, problems of the K+ homeostasis during long lasting low level muscle activity are discussed as reasons of limiting performance. Changes in the potassium distribution between intra- and extracellular space have enormous consequences for excitability, contractili, metabolism, and arterial blood pressure. Finally references are given for evaluation and designing of modern work.