Time course of changes in the human Achilles tendon properties and metabolism during training and detraining in vivo

Abstract

The purpose of this study was to investigate the time course of changes in human tendon properties and metabolism during resistance training and detraining. Nine men (21-27 years) completed 3 months of isometric plantar flexion training and another 3 months of detraining. At the beginning and on every 1 month of training and detraining periods, the stiffness, blood circulation (blood volume and oxygen saturation), serum procollagen type 1 C-peptide (P1P; reflects synthesis of type 1 collagen), echointensity (reflects collagen content), and MRI signal intensity (reflects collagen structure) of the Achilles tendon were measured. Tendon stiffness did not change until 2 months of training, and the increase (50.3%) reached statistical significance at the end of the training period. After 1 month of detraining, tendon stiffness had already decreased to pre-training level. Blood circulation in the tendon did not change during the experimental period. P1P increased significantly after 2 months of training. Echointensity increased significantly by 9.1% after 2 months of training, and remained high throughout the experiment. MRI signal intensity increased by 24.2% after 2 months and by 21.4% after 3 months of training, but decreased to the pre-training level during the detraining period. These results suggested that the collagen synthesis, content, and structure of human tendons changed at the 2-month point of training period. During detraining, the sudden decrease in tendon stiffness might be related to changes in the structure of collagen fibers within the tendon.

Sports and exercise-related tendinopathies: a review of selected topical issues by participants of the second International Scientific Tendinopathy Symposium (ISTS) Vancouver 2012

“…85 The maxim that 'tendons don't like rest or change' ( Jill Cook, ISTS 2012 workshop) should be instilled in athletes with a propensity for tendinopathy and be communicated to coaches who plan preseason training sessions.…”

Neuromuscular mechanics and hopping training in elderly

“…Another possibility is that a longer training period would be required for elderly tendon to increase its stiffness due to longer adaptation period to correct loading technique although changes have been observed in young individuals two months after the start of strength training (Kubo et al 2012). …”

The Achilles tendon is mechanosensitive in older adults: adaptations following 14 weeks versus 1.5 years of cyclic strain exercise

“…However, unlike in muscles, it has to be ensured that the exercise intervention implements tendon strains corresponding to high mechanical loading (intensities of at least 80-90% of MVC) to induce tendon adaptation (Arampatzis et al, 2007a;Grosset et al, 2014). Similar to adaptations to loading, a relatively fast deterioration in the tendon mechanical, material and morphological properties has been shown during bed rest and paralysis (Kubo et al, 2000;Maganaris et al, 2006;Reeves et al, 2005), as well as trainingdetraining studies (Kubo et al, 2012). Such fast adaptation caused by high loads and deterioration following disuse or detraining indicates that the homeostatic response to changes in mechanical loading is a relatively quick process, occurring within 12-14 weeks, in both younger and older adults.…”