Longitudinal Changes in Achilles Tendon and Medial Gastrocnemius Muscle Architecture During a 156-km Ultradistance Trail Running Event

This study aimed to assess the longitudinal changes in triceps surae muscle-tendon architecture to an ultra distance trail running. 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 Achille 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).