Elizabeth C. Fisher

Muscle strength and body composition: associations with bone density in older subjects

This study investigated the relationship between isokinetic muscle strength and bone density (SPA and DPA) in men and women aged 45-77 yr. Regression models were adjusted for age, weight, smoking status, and calcium supplementation. Elbow extensors (but not flexors) peak torque was correlated with radial density in men (partial r = 0.26, P < 0.05) and women (partial r = 0.24, P < 0.05). Knee flexor (but not extensor) peak torque in women was significantly correlated with spine density (partial r = 0.28, P < 0.05), and muscle mass was significantly correlated with Wards triangle density (partial r = 0.35, P < 0.05). No associations between knee flexor or extensor muscle strength and spine or femur bone density were observed in men. Fat-free mass (FFM, hydrodensitometry) was associated with all bone density sites in males and females (partial r = 0.30-0.55; P < 0.05). These results demonstrate that 1) significant associations observed between elbow extensor strength and radial bone density in men and women may reflect loading along the longitudinal axis of the radius associated with elbow extensor activity; and 2) significant associations exist between knee flexor muscle strength and lumbar density in women only. Additionally, the associations between FFM and bone density do not necessarily reflect associations between isokinetic muscle strength and bone density.

The reproducibility of the Bruce protocol exercise test for the determination of aerobic capacity in older women.

The reproducibility of the Bruce exercise test protocol for the determination of maximal aerobic activity was evaluated in sedentary older women. Seventeen women between the ages of 51 and 68 yr performed five maximal graded exercise tests to volitional fatigue on a treadmill. VO2max (mL.kg-1.min-1) values averaged 27.5 +/- 1.1; 28.3 +/- 1.3; 28.4 +/- 1.3; 29.6 +/- 1.5; and 28.2 +/- 1.4 for trials 1-5, respectively, and were not significantly different. Criteria for a plateau in VO2 at the point of exhaustion were met in 21 out of 85 tests (25%). The mean coefficient of variation VO2max for the subjects for the 5 tests was 6.5% (range, 2.0-14%). Pearsons correlation coefficients for the study variables were significant, indicating good agreement between repeated tests (r2: between 0.70 to 0.89). Although there were no significant differences among the mean VO2max values in the 5 trials, 11 subjects had a 1.0 ml.kg-1.min-1 or greater increase in the VO2max from test 1 to test 2, and only 6 subjects had no change or a decrease in VO2max. The mean difference between T2 and T3 was lower (T1 vs T2: 0.8 mL.kg-1.min-1, T2 vs T3: 0.1 mL.kg-1.min-1) indicating slightly better agreement between the second and third set. Estimates of the between and within subject variance revealed a low within subject variance (4.2 (mL.kg-1.min-1)2) compared to the between subject variance (22.1 (mL.kg-1.min-1)2). This study demonstrates that a commonly used exercise testing protocol generates highly reproducible measurements of VO2max in women between 51 and 68 yr. The mean differences between tests and the high level of agreement between repeated tests suggests that a single measurement of VO2max can be performed to assess functional aerobic capacity in this population.

Protein Metabolism and Endurance Exercise

In brief: The use of proteins as a source of energy has been discounted in the past. However, current research has demonstrated that amino acids can contribute to whole body metabolism. The availability of amino acids can be increased by either elevating the rate of muscle protein breakdown or decreasing the rate of muscle protein synthesis. Research indicates that there is a substantial decrease in the rate of protein synthesis during exercise. We estimate that protein can provide up to 5.5% of the total caloric cost of exercise. Because essential amino acid requirements have been determined only for resting persons, the recommended maximum protein requirements may not be adequate for physically active individuals.