JOURNAL OF BONE AND MINERAL RESEARCH Volume 9, Number 10, 1994 Mary Ann Liebert, Inc., Publishers zyxwvutsrqpo Effects of Free Mobilization and Low- to High-Intensity Treadmill Running on the Immobilization-Induced Bone Loss in Rats PEKKA KANNUS,' HARRl SIEVANEN,' TEPPO L.N. JARVINEN,2 MARKKU JARVINEN,* MARTTI KVIST,3 PEKKA OJA,' ILKKA VUORI,' zyxwv and LASZLO JOZSA4 ABSTRACT After an immobilization period of 3 weeks, the effects of free remobilization (8 weeks) as well as low- and high-intensity treadmill running on the bone mineral content (BMC) and density (BMD) of the hindlimbs of Sprague-Dawley rats zyxwvut (n zyxwvutsrqp = 70) were studied using a dual-energy x-ray absorptiometric scanner. In the low-intensity running program, the rats were allowed to move freely in the cage for 1 week, after which they started to run on a treadmill twice a day for zyxwvu 7 weeks. The speed of the treadmill was 20 cm/s, with an uphill inclination of 10". The running time was gradually increased from 20 minutes per session to 45 minutes per session. In the high-intensity group, the program was similar, with the exception that the speed of the treadmill was 30 crn/s, with an uphill inclination of 30". Immobilization for 3 weeks produced a significant BMC and BMD loss in the immobilized left femur and tibia (mean loss 9.6%, p < 0.001) but did not affect the right free limbs. Both low- and high-intensity running restored mineral content in the immobilized limb; however, an average 5% difference (p < 0.05) in mineral content of the right and left limb bones persisted. In the running groups, the values for the immobilized left limbs were at the same level or exceeded (range 3.8-11.6%, p < 0.05-0.01) and those of the free right limbs exclusively exceeded (range 5.3-15.9%,p < 0.05-0.01) the corresponding values of the age-matched control rats. In the group with free remobilization, the BMCs and BMDs always remained below those in the controls (range -3.2 to -12.6%, p values ranging from NS top < 0.01). Thus, this study showed the need for greater than normal activity to restore the BMC and BMD from disuse to normal. INTRODUCTION OTH HUMAN' AND ANIMAL" Is' studies have shown that B physical exercise can increase the bone mineral content (BMC) and density (BMD) of a healthy bone. but there is still uncertainty about the frequency, intensity, duration, and type of activity that provides maximum anabolic stimulus to bone.( 12.16- 18) The osteogenic effects of training seem to be quite specific to the anatomic sites at which mechanical strains Overactivity may in turn have a negative occur,l 12.Ih. 19.201 effect on bone mass,(lh.21-23) and the positive effect of training disappears relatively quickly if the subject returns to the previ- ous level of a~tivity.'~.l~.''.*~' Immobilization is a frequently used treatment for soft tissue and bone injuries despite resulting muscle and bone atro- phy,(12.25-32) Immobilization stimulates bone resorption and depresses bone formation (especially in trabecular bone), result- ing in osteoporosis; that is, the bone mass decreases with respect to its volume along with simultaneous deterioration in the material and geometric properties of the bone, but the ratio between calcified and noncalcified matrix, as well as the chemical composition of bone, remains essentially un- 'President Urho Kaleva Kekkonen Institute for Health Promotion Research and Tampere Research Station of Sports Medicine. Tampere. Finland. 'Department of Biomedical Sciences, University of Tampere, and the Department of Surgery, Tampere University Hospital, Tampere, Finland. 'Sports Medical Research Unit, Paavo Numi Center, Turku, Finland. Department of Morphology, National Institute of lraumatology, Budapest. Hungary. 1613