RESUMO
Physical activity is an important factor for maintaining and probably increasing bone mass in humans. However, the mechanism by which this takes place is not completely understood. The purpose of this study was to examine the influence of physical exercise on serum alkaline phosphatase (ALP) and in particular, the bone isoforms of ALP. Six ALP isoforms were quantified by high-performance liquid chromatography: three bone (B/I, B1, and B2), and three liver ALP isoforms. In addition, serum calcium, parathyroid hormone (PTH), and other markers of bone formation and degradation, as measured by osteocalcin and cross-linked carboxyterminal telopeptide of type I collagen (ICTP), were analyzed. The study groups comprised 15 women, 8 postmenopausal (range 51-62 years) and 7 near age of peak bone mass (range 21-27 years). When the postmenopausal women exercised on an ergometer cycle until exhaustion we found significant increases in serum of bone ALP isoforms B1 and B2, and phosphate, even considering the hemoconcentration that occurred during the exercise. When the young women jogged in a moderate tempo for 40-40 minutes the levels of serum B2 and PTH increased. All changes turned towards baseline within 20 minutes after exercise. In conclusion, exercise increased serum ALP bone isoforms B1 and B2, and their responses were differentiated. As B1 and B2 are known to represent specific bone compartments, cortical and trabecular bone, the present findings may indicate different effects on bone of weight- and nonweight-bearing exercise.