Muskelarbeit

Muskelarbeit is the mechanical work performed by skeletal muscles during contraction. In physics, work is defined as the integral of force along the movement path, and for a muscle around a joint it can be expressed as W = ∫ τ dθ, where τ is the joint torque and θ the angular displacement. In simple terms, Muskelarbeit is the energy transferred to move a body segment or to resist external loads.

The sign of the work depends on the contraction type. Concentric contractions shorten the muscle and typically produce positive work on the moving segment; eccentric contractions lengthen the muscle while under load and yield negative mechanical work (the external load does work on the muscle); isometric contractions generate force without movement and do zero mechanical work.

Muskelarbeit is influenced by factors such as muscle force, contraction velocity, tendon elasticity, joint geometry, and neural activation. Biochemically, muscles convert chemical energy (ATP) into mechanical work and heat, so metabolic energy expenditure often exceeds the mechanical work performed. Gross efficiency for human muscle ranges roughly around 20–25%, varying with task and conditions.

In biomechanics, external work refers to the work done on the environment (for example lifting or propelling the body), while internal work accounts for energy spent in moving body segments. Measurements of Muskelarbeit commonly use force plates and motion analysis, sometimes complemented by estimates from joint power.

Applications include gait analysis, rehabilitation, ergonomics, and sports science. Power, the rate of doing work, is defined as P = dW/dt.