Purpose: to study the effect of estrogen replacement on muscle hypertrophy in response to 12 weeks resistance training in postmenopausal women Hypothesis: Transdermal administration of 17-β estradiol enhance the anabolic effect of resistance training on muscle mass, strength in postmenopausal women Primary outcome: Muscle hypertrophy (muscle CSA, muscle fiber type specific CSA) Secondary outcome: Messenger RiboNucleic Acid (mRNA)(real-time PCR), protein (western blotting), satellite cell proliferation and activation, Strength, functional test, muscle protein synthese.

Design: Two groups of healthy postmenopausal women (½-5 years after menopause) who have not performed regular resistance exercise (<1 times per week) the last two years. Randomized, controlled intervention study +/- transdermal administration of estrogen (17-β estradiol). Both groups perform 12 weeks of supervised progressive resistance training (3/week) aiming to induce muscle hypertrophy in the legs.

Inclusion Criteria:

• Postmenopausal women, more than 6 months, but less than 5 years since last menstruation.

Exclusion Criteria:

• Less than 2 hours exercise with moderate to high intensity per week the last year, no regular resistance exercise the last 2 years (less than 5 exercise bouts during the last year)
• No previous or present lower limb injuries which may hinder participation in strength training
• No use of medicine which may influence the adaptation to strength training such as regular use of nonsteroidal anti-inflammatory drugs and use of statins, no muscle
• Joint or metabolic diseases or other chronic diseases that would affect the results of the investigation, high blood pressure (>140/90), smoking