Effect of habitual exercise on the structural and mechanical properties of human tendon, in vivo, in men and women

We examined whether long-term habitual training (a) was associated with differences in structural and mechanical properties in tendon in women and (b) yielded different tendon properties in men and women. Ten male runners, 10 female runners and 10 female non-runners were tested. Tendon cross-sectional area (CSA) and length of the patellar and Achilles tendon were determined with MRI. Ultrasonography-based measurement of tendon elongation and force during isometric contractions provided mechanical properties. Distal patellar and Achilles tendon CSAs were greater than the proximal part in all three groups (P < 0.05). Weight-normalized Achilles tendon CSA were similar in trained (2.78 +/- 0.17 mm(2)/kg(3/4)) and untrained women (2.60 +/- 0.13 mm(2)/kg(3/4)), while that in trained men (3.77 +/- 0.27 mm(2)/kg(3/4)) was greater compared with trained women (P < 0.01). Patellar tendon CSA were comparable in trained and untrained women, while that in trained men was greater compared with trained women (P < 0.01). Patellar tendon stiffness was greater in male runners (3528 +/- 773 N/mm) compared with female runners (2069 +/- 666 N/mm) and non-runners (2477 +/- 381 N/mm), (P < 0.01), but patellar tendon deformation, stress, strain and modulus were similar. These data indirectly suggest that the ability of Achilles and patellar tendons to adapt in response to habitual loading such as running is attenuated in women.