BUTTERFIELD, T. A. Eccentric exercise in vivo: strain-induced muscle damage and adaptation in a stable system. Exerc. Sport Sci. Rev., Vol. 38, No. 2, pp. 51-60, 2010. The muscle tendon unit is a stable system, designed to operate eccentrically with efficiency and resiliency. Fiber strains, although minimized by tendon compliance during exercise, are essential components to decoding the mechanical and chemical signals during exercise. Subsequent cellular adaptations minimize the subsequent "dose" of stress and strain and serve to limit the exacerbation of damage into injury.