Longitudinal changes in Achilles tendon and triceps surae muscle architecture during a 156-km mountain ultramarathon.

Abstract

This study aimed to assess the longitudinal changes in triceps surae muscle-tendon architecture to an mountain ultramarathon. Experienced trail runners (N=55, 78% men, age: 45.2 [13.5] years) participated in a 156-km trail run (6000m climbing) consisting in six 26-km laps. The resting architectural properties of triceps surae muscle-tendon were measured using ultrasound imaging for Achilles tendon cross-sectional area (AT CSA), medial gastrocnemius muscle pennation angle, thickness, length and fiber length. Measurements were performed the day before the race (Baseline), at 52-km (T1), at 104-km (T2), at 156-km (T3) and 12 hours after the race (H12). Among finishers (n=41), there was a significant biphasic change in AT CSA during the race (P = 0.001). Firstly, a significant decrease in AT CSA occurred between Baseline and T1 (P = 0.006), with greater decrease for participants averaging speed >8 km/h (p = 0.014). Secondary, there was a significant increase in AT CSA especially between T2 and T3 (P = 0.006) that was correlated with a decrease in average speed (P = 0.001) and alteration of spaciotemporal running parameters (p < 0.05). Changes in muscle-tendon architecture was not significantly different between finishers (n=41) and non-finishers (n=14). In 47 participants (85.5%) who completed the follow-up, AT CSA at H12 was greater compared to Baseline (P = 0.010). The main finding is the significant and biphasic modification of the AT CSA during a 156-km mountain ultramarathon with an initial decrease corresponding to mechanical stress followed by a secondary increase suggesting adaptive mechanotransduction persisting after 12 hours.