Maximal strength training improves muscle-tendon properties and increases tendon matrix remodulation in well-trained triathletes.

This study assessed the effects of a 12-week strength training (ST) intervention on Achilles and patellar tendon stiffness and tendon-matrix blood-borne markers in well-trained triathletes performing concomitant high-volume aerobic training. Eighteen triathletes (VO(2)max: 64.43 ± 4.65 ml kg(-1) min(-1)) were randomized into a combined endurance and ST group (3-times/week; intervention) or endurance-only group (control). Pre- and post-intervention assessments included ultrasound-based force-elongation measurements of the Achilles and patellar tendons, blood analysis of selected markers before and after an experimental ST session in weeks 1 and 12, and dynamic strength and endurance testing. Achilles (39.1 ± 31.8%) and patellar tendon stiffness (15.8 ± 8.5%), isometric maximal knee extensor strength (8.9 ± 5.7%), and squat one-repetition maximum (20.0 ± 9.7%) significantly increased in the intervention group (all p ≤ 0.002). Additionally, serum concentrations of matrix metalloproteinase (MMP) I (46.30 ± 20%; p = 0.027) and decorin (30.50 ± 19.94%; p = 0.015) increased after the first experimental ST session, while after the second session MMP-III (40.77 ± 20.13%; p = 0.040) and decorin (36.59 ± 37.81%; p = 0.007) were increased. Baseline tenascin-c concentrations decreased significantly only in the control group (-19.49 ± 20.55%; p = 0.029). Our data clearly show improved muscle-tendon properties of the plantar flexor muscles and quadriceps femoris, indicating Achilles and patellar tendon stiffness to be similarly responsive to heavy ST despite concomitantly performing high volumes of endurance training.