Hvilelengde

Hvilelengde, or resting length, is the length of an object or tissue when no external forces are applied. For elastic materials, it is the natural, stress-free length. In many contexts hvilelengde serves as a reference point for measuring extension or compression.

In engineering and physics, hvilelengde denotes the length at which internal forces are zero. If the object is shortened or elongated beyond this length, restoring forces arise. Rest length is used to design springs, polymers, and structural components, where deviations determine stiffness and load response.

In physiology, hvilelengde commonly refers to the resting length of a muscle or its fibers. At or near this length the sarcomere arrangement allows optimal overlap of actin and myosin for active contraction; moving away from this length reduces active tension and increases passive tension due to connective tissues and the structural proteins.

The hvilelengde can vary between muscles, individuals, and species and is influenced by joint angle and tone. It is a key parameter in biomechanical models of movement, rehabilitation, and athletic training because it affects force production and range of motion.

Related concepts include the length-tension relationship, resting length, slack length, and elasticity.