The effect of acute exercise on collagen turnover in human tendons: influence of prior immobilization period

Mechanical loading of human tendon stimulates collagen synthesis, but the relationship between acute loading responses and training status of the tendon is not clear. We tested the effect of prolonged load deprivation on the acute loading-induced collagen turnover in human tendons, by applying the same absolute load to a relative untrained Achilles tendon (2-week immobilization period prior to acute loading) and a habitually loaded contra-lateral Achilles tendon, respectively, within the same individuals. Eight untrained, healthy males had one lower limb totally immobilized for 2 weeks, whereas the contra-lateral leg was used habitually. Following the procedure both Achilles tendons and calf muscles were loaded with the same absolute load during a 1-h treadmill run. Tissue collagen turnover was measured by microdialysis performed post-immobilization but pre-exercise around both Achilles tendons and compared to values obtained by 72-h post-exercise. Power Doppler was used to monitor alterations in intratendinous blood flow velocity of the Achilles tendon and MRI used to quantitate changes in tendon cross-section area. Acute loading resulted in an increased collagen synthesis 72 h after the run in both Achilles tendons (p < 0.05) with no significant difference. No signs of acute tendon overloading were demonstrated by Power Doppler, and tendon cross-section area did not change as a result of immobilization and reloading. The present study indicates that 2 weeks of tendon load deprivation is not sufficient to affect the normal adaptive response to loading determined as increased collagen synthesis of peritendinous Achilles tendon tissue in humans.