Twenty weeks of weight training increases lean tissue mass but not bone mineral mass or density in healthy, active young women P.D. Chilibeck, A. Calder, D.G. Sale, and C.E. Webber Abstract: Twenty young women (20.3 ± 1.0 years) participated in a weight training program in which upper and lower body exercises were done twice per week for 20 weeks. Ten other women (20.2 ± 0.4 years) served as a control group. Training resulted in significant ( p < 0.05) increases in arm curl (73%), bench press (33%), and leg press (23%) lifting performance. Whole body (3.7%), trunk (3.0%), arm (9.7%), and leg (3.3%) lean tissue mass also increased significantly, based on measurements made by dual energy x-ray absorptiometry (DEXA). Changes in the control group were small and nonsignificant. In contrast, training did not increase DEXA-measured bone mineral content (BMC) and density (BMD) in a whole body measure nor in arm, leg, ribs, thoracic and lumbar spine, and pelvis segments. Similarly, hip BMC and BMD at femoral neck, trochanter, intertrochanter, and Ward’s triangle sites, and total hip did not increase with training. The data indicate that a resistance training program that effectively increases strength and lean tissue mass in young women may fail to increase BMC or BMD over a 20-week training period. Key words: strength, body composition. Résumé : Vingt jeunes femmes (20,3 ± 1,0 ans) ont participé à un programme d’entraînement avec poids et haltères impliquant les membres inférieurs et supérieurs, à raison de deux fois par semaine, pendant 20 semaines. Dix autres femmes (20,2 ± 0,4 ans) ont fait partie d’un groupe témoin. L’entraînement a induit des augmentations significatives ( p < 0,05) de la performance en ce qui a trait à l’extension des jambes (23%), au développé-couché (33%) et à la flexion des bras (73%). La masse tissulaire maigre des jambes (3,3%), des bras (9,7%), du tronc (3,0%) et du corps entier (3,7%) a aussi augmenté de manière significative, tel qu’indiqué par les mesures effectuées par absorptiométrie double énergie à rayons X (ADEX). Chez le groupe témoin, les variations ont été faibles et non significatives. À l’opposé, l’entraînement n’a augmenté ni la densité (DMO) ni le contenu (CMO) minéral osseux, mesurés par ADEX, dans le corps entier et dans des segments de bras, de jambes, de côtes, de régions lombaires et thoraciques de la colonne et de bassin. L’entraînement n’a pas augmenté non plus le CMO ni la DMO de la hanche au niveau du col du fémur, du trochanter, de l’intertrochanter, du triangle de Ward et de la hanche totale. Les résultats indiquent qu’un programme d’entraînement de force avec résistance, qui augmente efficacement la force et la masse tissulaire maigre chez les jeunes femmes, pourrait ne pas augmenter le CMO ou la DMO sur une période d’entraînement de 20 semaines. Mots clés : force, composition corporelle. [Traduit par la Rédaction] Introduction Osteoporosis is a growing health problem; osteoporotic frac- tures are increasing at a faster rate than the increase in average age (Martin et al. 1991). Exercise has been promoted as a pre- ventative measure against osteoporosis, as more active people generally have greater bone mineral density (BMD) (Alekel et al. 1995) and decreased incidence of osteoporotic fractures (Cooper et al. 1988). For women, who are at greater risk of osteoporosis later in life, the increase in BMD and bone mineral content (mass, BMC) that naturally occurs during the third decade of life is favourably augmented by physical activity (Recker et al. 1992); thus, this may be a crucial decade in which to maximize BMD and BMC in women, using the type of exercise consid- ered most effective for this purpose. Strength training (most commonly practised as weight training) may be the most effective type of exercise for increas- ing BMD and BMC for three reasons. First, strength training imposes loads on bone that are dynamic (versus static), large in strain magnitude, and irregularly distributed. This pattern of bone loading has been found to be most effective in increasing bone formation in animals (Lanyon et al. 1982; Lanyon and Rubin 1984; Rubin and Lanyon 1985). Second, cross-sectional studies show that young female strength-trained athletes have greater BMD than endurance-trained individuals and un- trained subjects (Davee et al. 1990; Heinonen et al. 1993). Third, both within groups of young female athletes and within the general female population, a positive correlation has been found between muscle strength and (or) muscle mass and BMD and (or) BMC (Doyle and Brown 1970; Eickhoff et al. 1993; Nichols et al. 1995; Snow-Harter et al. 1990). In light of this evidence implying the effectiveness of Received January 5, 1996. P.D. Chilibeck, A. Calder, D.G. Sale, 1 and C.E. Webber. Departments of Kinesiology and Nuclear Medicine, McMaster University, Hamilton, ON L8S 4K1, Canada. 1 Author for correspondence. Can. J. Physiol. Pharmacol. 74: 1180 – 1185 (1996). 1180 © 1996 NRC Canada