Abstract
Introduction
Tendon cross-sectional area (CSA) and stiffness increase in men during chronic exercise. The increase in tendon CSA and stiffness is not evident in women. In men, exercise increases tendon production of MMPs, IGF-1, and IL-6, which presumably contribute to tendon remodeling during chronic exercise. The purpose of this study was to determine if exercise-induced production of MMPs, IGF-1, and IL-6 are limited in women when compared to men.
Materials and Methods
Young men (n=9, 27±1 y) and women (n=8, 26±1 y) performed a single bout of calf press exercise (8 sets of 15 repetitions at 70% of 15-RM). A microdialysis fiber (3000 kDa cut-off) was inserted into the space anterior to the Achilles tendon immediately after exercise and during a control experiment. All proteins were evaluated with ELISA kits.
Results
In men IGF-I increased with exercise at 3 (p<0.05) but not 4 hrs. IGF-1 was not elevated at any measured time points in women. IL-6 increased with exercise to a similar extent in men and women at 3 hrs (p<0.05) but values returned to baseline at 4 hrs. MMP-9 increased with exercise at both 2 and 5 hours (p<0.05) in men but not in women. MMP-2 increased with exercise at 2 and 5 hrs to a similar extent in both men and women (p<0.05). In men TIMP-1 increased with exercise at 2 (p<0.05) but not 5 hrs. In women, TIMP-1 levels were elevated post-exercise at both 2 and 5 hrs (p<0.05).
Discussion
In men, resistance exercise resulted in a modest and transient increase in tendon production of IGF-1 and IL-6. In women, this is only evident for IL-6. MMP-2 and MMP-9 increased with exercise in men. The exercise-induced increase in MMP-9 was not seen in women. In contrast, MMP-2 increased in women to a comparable magnitude as men. TIMP-1 increased with exercise in men and women but remained elevated out to 5 hrs in women only. The blunted increase in IGF-1 and MMP-9 and a prolonged increase in TIMP-1 may contribute to the lack of tendon adaptations after chronic training in women when compared to men.
