Journal of Medical and Biological Engineering, 21(2): 75-78 2001 75 Functional Adaptation of Bone Ronald F. Zernicke *,1,2,3 Gregory R. Wohl 1,2 Steven K. Boyd 1,2 Stefan Judex 4 1 McCaig Centre for Joint Injury and Arthritis Research, Alberta, Canada 2 Departments of Mechanical Engineering and Manufacturing Engineering, and 3 Faculty of Kinesiology , University of Calgary, Alberta, Canada 4 Department of Biomedical Engineering, State University of New York, Stony Brook, New York, USA Received 3 January 2001; Accepted 6 March 2001 Abstract Bone adapts to altered mechanical stimuli, dietary changes, or injury. Dietary calcium and vitamins play significant roles in maintaining skeletal health, but high-fat diets may contribute to osteopenia. Exercise, generally, helps to maintain bone mass and counter osteoporosis, but highly strenuous exercise can also have detrimental effects on bone— particularly for immature bone. Negative exercise effects may also be linked to diet, as insufficient dietary protein can impair bone development and remodeling during periods of intense exercise. Bone remodeling can contribute to tissue repair, but chronically altered loading after a joint injury can stimulate remodeling processes that negatively influence the joint. Anterior cruciate ligament injury at the knee, for example, commonly leads to osteoarthritis, and early changes in the periarticular cancellous bone may contribute to the development of knee osteoarthritis. Each of these factors can influence skeletal health, but the mechanisms remain unclear by which bone interprets its environment and responds to physical stimuli or injury. To understand why different levels of exercise are beneficial or detrimental and why altered joint loading leads to changes in periarticular bone structure, underlying mechanisms must be understood by which bone interprets its mechanical environment. Mechanical stimuli, diet, and injury have potent influences on skeletal health and function, but the underlying mechanisms for these adaptations are incompletely understood. Here, we review our research that provides important insights into bone adaptation processes. Keywords: Bone, Adaptation, Diet, Exercise Introduction Nutritional and metabolic factors are two of the predominant influences on bone morphology, mechanical properties [1], and mineral content. Diets high in fat and sucrose (HFS) can produce pronounced negative effects on the skeletal system. For example, young rats fed an HFS diet had inferior bones compared with age-matched controls fed a low- fat complex carbohydrate diet [1] (Table 1, adapted from [2]). Deleterious HFS diet effects on L6 vertebra and femoral neck were due to reductions in both bone material and structural properties [3]. Conversely, tibial morphology was not affected by the diets [4]. The significant decreases in HFS tibial structural properties were related to the reduction in bone material properties. The HFS metatarsus had a cross-sectional area that was greater than controls [4]. Though there were significant reductions in HFS metatarsal bone material properties, there were no differences in metatarsal structural properties. Thus, * Corresponding author: Ronald F. Zernicke Tel: +403-220-5607; Fax: +403-220-0448 E-mail : zernicke@ucalgary.ca diet differentially affected the immature rat skeleton. In high- metabolism regions containing trabecular bone (L6 vertebra and femoral neck) decrements in bone structural properties were due to a combination of reduced bone material properties and changes in bone morphology. In cortical bones of the appendicular skeleton, decrements in structural properties were due to reductions in bone material properties. High-sucrose diets in the rat elevated blood insulin levels and induced hyperinsulinemia, which in turn produced hypercalciuria. Calcium deficiencies and high insulin levels produced poor bone mineralization and adversely influenced bone mechanical properties. In a long-term study, the HFS diet did not stimulate adaptation to arrest progressive osteopenia [5]. After two years, HFS rats had significantly greater body mass than the control rats (low-fat, complex carbohydrate diet), but HFS femoral necks and L6 vertebra were mechanically inferior. Methods Regular, prolonged exercise can help maintain bone mass and counter osteoporosis. As well, active children can reach higher peak bone mass in early adulthood than sedentary