Tendinopathy impairs the functional and morphological entity of the Achilles tendon (AT). Oral supplementation of non-essential amino acids can alleviate inflammatory responses and help faster healing of Achilles tendinopathy, but this has not been substantiated in human AT.
PURPOSE: To investigate the effects of oral supplementation of the amino acid mixture on mechanical (stiffness) and morphological (size and echogenic) properties of AT and biochemical variables in humans.
METHODS: Sixteen males with existing discomfort of AT (e.g. swelling, dull pain, and stuck feeling during exercise) participated in a double-blinded placebo-controlled study. Participants were randomly assigned to Active (n = 8, mean ± SD: 22.9 ± 2.9 years) or Placebo (n = 8, 23.6 ± 6.0 years) groups. Participants consumed 4 g of test food 3 times/day for 2 weeks. On pre- (Day1) and post-2 weeks supplementation (Day15), ultrasound shear wave velocity (SWV) of AT at two different sites (calcaneal insertion and the most distal attachment of the soleus, MTJ) was measured every 10°, from 30° ankle plantar flexion to 10° dorsiflexion (every 10°). AT thickness and ultrasonic echo intensity, and biochemical variables in the sampled blood were also measured.
RESULTS: On Day15, Active group showed higher SWV values (6.6 ± 1.3 m/s) at the calcaneal insertion (ankle 30°) than Placebo group (6.2 ± 0.7 m/s) (p < 0.05), while at 10° dorsiflexion, SWV values at MTJ were significantly lower in Active (14.1 ± 1.3 m/s) than in Placebo group (14.5 ± 0.5 m/s) (p < 0.05). On Day15, AT echo intensity was significantly higher in Active (104.7 ± 5.7) than in Placebo group (97.3 ± 8.1) (p < 0.05). TNF-α and uric acid were significantly lower in Active (2.1 ± 0.9 pg/ml and 5.5 ± 1.1 mg/dl, respectively) than in Placebo group (2.7 pg/ml ± 1.4 and 8.1 ± 2.0 mg/dl, respectively).
CONCLUSIONS: The SWV results suggest that AT becomes stiffer and more resilient at its resting length and is subject to less mechanical stress under stretch by the intervention. The observed changes were accompanied by favorable changes in biochemical markers. Our results suggest efficacy of the present amino acid mixture for the faster healing of Achilles tendinopathy.