At any time, a tendon undergoes both catabol ic and anabolic processes. Under conditions of normal loading, these pro- cesses are balanced and provide the basis for a healthy homeostatic state within the tissue. This balance may be disturbed by the type, intensity and frequency of loading (see Magnussen et al. [20] for a detailed review). A load may be applied to a tendon longitudinal to its collagen fibres (tension or tensile load) or perpendicular to the line of the fibres (compression), the latter particularly at its bony enthesis. Tensile loads may be applied actively via muscle contraction or passively via stretching. Tendon loads will be particularly high when the muscle is active and the tendon is lengthening at the same time, i.e. ec- centric contractions in the outer range, where anatomical compression may also occur [21].