Submitted on November 3, 2008
Revised on January 8, 2009
Accepted on January 15, 2009
Combination of hormone replacement therapy and high physical activity is associated with differences in Achilles tendon size in monozygotic female twin pairs
Taija Finni1*, Vuokko Kovanen2, Paula HA Ronkainen2, Eija Pöllänen2, Gregory R. Bashford3, Jaakko Kaprio4, Markku Alen2, Urho M. Kujala2, and Sarianna Sipilä5
1 University of Jyvaskyla
2 University of Jyväskylä
3 University of Nebraska-Lincoln
4 University of Helsinki
5 University of Jyvaskylä,
* To whom correspondence should be addressed. E-mail: Taija.Finni{at}jyu.fi.
Estrogen concentration has been suggested to play a role in tendon abnormalities and injury. In physically active postmenopausal women hormone replacement therapy (HRT) has been suggested to decrease tendon diameter. We hypothesized that HRT use and physical activity are associated with Achilles tendon size and tissue structure. Study applied co-twin analysis of fourteen 54-62-yr-old identical female twin pairs with current discordance for HRT use for an average of seven years. Achilles tendon thickness and cross-sectional areas were determined by ultrasonography and tendon structural organization was analyzed from the images using linear discriminant analysis (LDA). Maximal voluntary and twitch torques from plantarflexor muscles were measured. Serum levels of estradiol, estrone, testosterone and sex hormone binding globulin were analyzed. Total daily metabolic equivalent score (MET-hours/day) was calculated from physical activity questionnaires. Results showed that in five physically active (MET>4) pairs the co-twins receiving HRT had greater estradiol level (p=0.043) and smaller tendon cross-sectional area than their sisters (63mm2 vs. 71mm2, p=0.043). Among all pairs, Achilles tendon thickness and cross-sectional area did not significantly differ between HRT using and non-using twin sisters. Intrapair correlation for Achilles tendon thickness was high despite HRT use discordance (r=0.84, p<0.001). LDA distinguished different tendon structure only from 2/6 examined twin pairs who had similar level of physical activity. In conclusion, the effect of HRT on Achilles tendon characteristics independent of genetic confounding may be present only in the presence of sufficient physical activity. In physically active twin pairs the higher level of estrogen seems to be associated with smaller tendon size.
