In this study adaptations in body composition, physical fitness and metabolic health were examined during 21 weeks of endurance and/or strength training in 39- to 64-year-old healthy women. Subjects (n = 62) were randomized into endurance training (E), strength training (S), combined strength and endurance training (SE), or control groups (C). S and E trained 2 and SE 2 + 2 times in a week. Muscle strength and maximal oxygen uptake (VO(2)max) were measured. Leg extension strength increased 9 +/- 8% in S (P < 0.001), 12 +/- 8% in SE (P < 0.001) and 3 +/- 4% in E (P = 0.036), and isometric bench press 20% only in both S and SE (P < 0.001). VO(2)max increased 23 +/- 18% in E and 16 +/- 12% in SE (both P < 0.001). The changes in the total body fat (dual X-ray absorptiometry) did not differ between groups, but significant decreases were observed in E (-5.9%, P = 0.022) and SE (-4.8%, P = 0.005). Lean mass of the legs increased 2.2-2.9% (P = 0.004-0.010) in S, SE and E. There were no differences between the groups in the changes in blood lipids, blood pressure or serum glucose and insulin. Total cholesterol and low-density lipoprotein cholesterol decreased and high-density lipoprotein cholesterol increased in E. Both S and SE showed small decreases in serum fasting insulin. Both endurance and strength training and their combination led to expected training-specific improvements in physical fitness, without interference in fitness or muscle mass development. All training methods led to increases in lean body mass, but decreases in body fat and modest improvements in metabolic risk factors were more evident with aerobic training than strength training.