Relationship between leg bone mineral values and muscle strength in women with different physical activity

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Abstract
This study examines whether knee extensor muscle isometric, isokinetic, and isoinertial strength values in women with different physical activity and body composition patterns are related to leg bone mineral density (BMD) and bone mineral content (BMC) values. A total of 129 women aged 17–40 participated in this study. They were divided into four groups: strength-trained (n = 33), endurance-trained (n = 32), normal weight sedentary (n = 41), and overweight sedentary (n = 23) women. In addition, the subjects were grouped as physically active (n = 65) or sedentary (n = 64) women. BMD and BMC for both legs (LBMD and LBMC, respectively) and for the dominant leg alone (DLBMC), body fat percentage and lean body mass (LBM), maximal knee extension isometric (ISOM) and isokinetic (ISOK) strength at the angular velocity of 60 deg·s−1, and isoinertial leg explosive strengths (countermovement jump CMJ) were measured. In endurance-trained women, LBMD was dependent on body mass index (BMI) (33.7% of the variance, R 2 × 100), and in the physically active group and the total group with LBM (14.6% and 15.6%, respectively). In the overweight group, LBMD was dependent on ISOK strength (21.7% of the variance, R 2 × 100). In the sedentary and total groups, ISOM strength was more important (10.3% and 5.0%, respectively); in the strength-trained group, body weight influenced LBMC, accounting for 71.6% of the variance (R 2 × 100). In the endurance-trained women, height influenced LMBC (37.9%, R 2 × 100). In sedentary and overweight women, LBM accounted for 52.1% and 61.4% of the total variance in LBMC. In these groups, ISOM strength accounted for 15.3% and 25.9% of the variance in LBMC. In overweight women, ISOM and ISOK strength together influenced LBMC highly (64.8% of the variance, R 2 × 100). In the sedentary group, the influence of LBM on LBMC was higher than in the active group (82.1% and 50.5% of the variance, respectively). In the total group, LBM influenced LBMC, accounting for 54.5% of the variance (R 2 × 100). ISOM strength (22.7%) alone or in combination with ISOK strength (35.8%) and CMJ (41.7%) (R 2 × 100) in LBMC in the sedentary group explained the variance. In the total group, ISOM strength alone (13.2%) or in combination with CMJ (17.1%) influenced LBMC (R 2 × 100). Our results suggest that (1) muscle strength and anthropometrical parameters were associated with LBMD; (2) LBM and ISOM strength had a significant relationship with DLBMC and LBMC only in nonathletic women; and (3) strength measured with different regimens highly influenced LBMC compared with LBMD, especially in the sedentary groups.