Soft tissue injury of tendons represents a major problem within sports medicine. Although several animal and cell culture studies have addressed this, human experiments have been limited in their ability to follow changes in specific tissue directly in response to interventions. Recently, methods have allowed for in vivo determination of tissue concentrations and release rates of substances involved in metabolism, inflammation and collagen synthesis, together with the measurement of tissue blood flow and oxygenation in the peritendinous region around the Achilles tendon in humans during exercise. It can be demonstrated that this region experiences an increase in blood flow during both static and dynamic exercise, and that exercise causes increased metabolic activity, accumulation of inflammatory mediators (prostaglandins) and increased formation of collagen type I in response to acute exercise. This coincides with a surprisingly marked drop in tissue pressure during contraction. With regards to both circulation, metabolism and collagen formation, peritendinous tissue represents a dynamic, responsive region that adapts markedly to acute muscular activity.