Trial objectives and purpose: The primary aim is to study the effects of moderately increased testosterone concentration on aerobic performance (endurance running time to exhaustion), and secondary aims to investigate the effects on submaximal work on treadmill, anaerobic capacity, muscle strength, body composition, behaviour and well-being, blood parameters, steroid hormone profile, gynecological parameters and skeletal muscle parameters in young healthy women in a double-blind, randomized, placebo-controlled trial. Treatment: Ten weeks of transdermal treatment with testosterone cream 10 mg daily or placebo cream in a randomized design (1:1). Primary outcome: Aerobic performance (running time to exhaustion on treadmill) Secondary outcomes: 1. Submaximal work on treadmill (oxygen uptake, ventilation, heart rate, blood lactate and subjective rate of exhaustion) 2. Anaerobic performance (Wingate test) 3. Muscle strength (Cybex apparatus, force transducer, counter movement jump) 4. Body composition (Dual X-ray Absorptiometry: muscle mass, fat mass, bone mass) 5. Behaviour and well-being (Quality of life, Profile of mood state, Confidence Questionnaire, Aggression Questionnaire) 6. Blood parameters (hemoglobin, hematocrit, reticulocytes, ferritin, CRP) 7. Steroid hormone profile in blood and urine 8. Gynecological evaluation (ovarian and endometrial variables on ultrasound) 9. Skeletal muscle morphology, metabolic enzymes and muscle protein synthesis Study population: Fifty healthy menstruating women will be included in the study and randomized to treatment with testosterone or placebo. Inclusion criteria: 18-35 yrs of age; body mass index (BMI) 19-25; non-smoking; a moderate to high self-reported level of recreational physical activity; not taking hormonal contraception and willing to use highly efficient non-hormonal contraception during the study (intrauterine device, bilateral tubal occlusion, vasectomised partner, same-sex partner, or sexual abstinence); accepting to not participate in any sports competitive event during the study period plus one month. Exclusion criteria: the presence of cardiovascular, liver, biliary or renal disease; hyperlipidemia; uncontrolled high blood pressure; endocrinological disorder; oligomenorrhea (menstrual intervals of more than 6 weeks) or amenorrhea (no menstruation for at least 3 months); pregnancy; a history of thromboembolic disorder; any malignancy; and intake of hormonal contraception the last two months prior to the study.
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Aerobic performance
Timeframe: Baseline and 10 weeks of treatment