Running Exercise for Short Duration Increases Bone Mineral Density of Loaded Long Bones in Young Growing Rats

Running Exercise for Short Duration Increases Bone Mineral Density of Loaded Long Bones in Young Growing Rats

YOSHINOBU HAGIHARA,¹ ARATA NAKAJIMA,¹ SATOSHI FUKUDA,² SUMIO GOTO,¹ HARUZO IIDA² and MASASHI YAMAZAKI¹

¹Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, Chiba, Japan
²International Space Radiation Laboratory, National Institute of Radiological Sciences, Chiba, Japan

Running exercise is an effective therapy for the prevention of osteoporosis; however, appropriate duration of exercise has not been determined. We therefore investigated the effect of exercise duration on bone mineral density (BMD) and systemic bone metabolism using young growing rats. Fifteen 8-week-old female Wistar rats were divided into three groups according to running load: control group (no running), short duration (30 min/day) and long duration (180 min/day), and animals ran on a treadmill 5 days per week over an 8-week period. BMD of the tibia was measured using peripheral quantitative computed tomography, and serum levels of tartarate-resistant acid phosphatase (TRAP), a bone resorption marker and alkaline phosphatase (ALP), a bone formation marker were measured to know whether the treadmill exercise would affect systemic bone metabolism. Short-duration running exercise (30 min/day) caused a significant increase in BMD of the metaphyseal trabecula (p < 0.05) with a reduction of serum TRAP levels (p < 0.01) and an increase in serum levels of calcium (p < 0.05) and phosphorus (p < 0.01). Conversely, long-duration exercise (180 min/day) significantly reduced BMD of the diaphyseal and metaphyseal cortex and that of the diaphyseal trabecula with a significant reduction of serum ALP levels and a significant increase in serum phosphorus. These findings suggest that short-duration exercise may increase BMD through suppression of bone resorption, whereas long-duration exercise may reduce BMD through suppression of bone formation. Exercising for short duration but not prolonged exercise is recommended to increase BMD of loaded long bones.

keywords —— running exercise; duration; bone mineral density; bone formation; bone resorption.

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Tohoku J. Exp. Med., 2009, 219, 139-143

Correspondence: Masashi Yamazaki, M.D., Ph.D., Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan.

e-mail: masashiy@faculty.chiba-u.jp