Skeletal Muscle Mitochondrial Function and Fatigability in Older Adults.

BACKGROUND: Fatigability increases while the capacity for mitochondrial energy production tends to decrease significantly with age. Thus, diminished mitochondrial function may contribute to higher levels of fatigability in older adults. METHODS: The relationship between fatigability and skeletal muscle mitochondrial function was examined in 30 participants aged 78.5 ± 5.0 years (47% female, 93% white), with a body mass index of 25.9 ± 2.7 kg/m(2) and usual gait-speed of 1.2 ± 0.2 m/s. Fatigability was defined using rating of perceived exertion (6-20 point Borg scale) after a 5-minute treadmill walk at 0.72 m/s. Phosphocreatine recovery in the quadriceps was measured using (31)P magnetic resonance spectroscopy and images of the quadriceps were captured to calculate quadriceps volume. ATPmax (mM ATP/s) and oxidative capacity of the quadriceps (ATPmax·Quadriceps volume) were calculated. Peak aerobic capacity (VO2peak) was measured using a modified Balke protocol. RESULTS: ATPmax·Quadriceps volume was associated with VO2peak and was 162.61mM ATP·mL/s lower (p = .03) in those with high (rating of perceived exertion ≥10) versus low (rating of perceived exertion ≤9) fatigability. Participants with high fatigability required a significantly higher proportion of VO2peak to walk at 0.72 m/s compared with those with low fatigability (58.7 ± 19.4% vs 44.9 ± 13.2%, p < .05). After adjustment for age and sex, higher ATPmax was associated with lower odds of having high fatigability (odds ratio: 0.34, 95% CI: 0.11-1.01, p = .05). CONCLUSIONS: Lower capacity for oxidative phosphorylation in the quadriceps, perhaps by contributing to lower VO2peak, is associated with higher fatigability in older adults.

Impact of body tilt on the central aortic pressure pulse.

The present work was undertaken to investigate, in young healthy volunteers, the relationships between the forward propagation times of arterial pressure waves and the timing of reflected waves observable on the aortic pulse, in the course of rapid changes in body position. 20 young healthy subjects, 10 men, and 10 women, were examined on a tilt table at two different tilt angles, -10° (Head-down) and + 45° (Head-up). In each position, carotid-femoral (Tcf) and carotid-tibial forward propagation times (Tct) were measured with the Complior device. In each position also, the central aortic pressure pulse was recorded with radial tonometry, using the SphygmoCor device and a generalized transfer function, so as to evaluate the timing of reflected waves reaching the aorta in systole (onset of systolic reflected wave, sT1r) and diastole (mean transit time of diastolic reflected wave, dMTT). The position shift from Head-up to Head-down caused a massive increase in both Tct (women from 130 ± 10 to 185 ± 18 msec P < 0.001, men from 136 ± 9 to 204 ± 18 msec P < 0.001) and dMTT (women from 364 ± 35 to 499 ± 33 msec P < 0.001, men from 406 ± 22 to 553 ± 21 msec P < 0.001). Mixed model regression showed that the changes in Tct and dMTT observed between Head-up and Head-down were tightly coupled (regression coefficient 2.1, 95% confidence interval 1.9-2.3, P < 0.001). These results strongly suggest that the diastolic waves observed on central aortic pulses reconstructed from radial tonometric correspond at least in part to reflections generated in the lower limbs.

Modelling body mass index and endometrial cancer risk in a pooled-analysis of three case-control studies.

OBJECTIVE: To quantify the relation between body mass index (BMI) and endometrial cancer risk, and to describe the shape of such a relation. DESIGN: Pooled analysis of three hospital-based case-control studies. SETTING: Italy and Switzerland. POPULATION: A total of 1449 women with endometrial cancer and 3811 controls. METHODS: Multivariate odds ratios (OR) and 95% confidence intervals (95% CI) were obtained from logistic regression models. The shape of the relation was determined using a class of flexible regression models. MAIN OUTCOME MEASURE: The relation of BMI with endometrial cancer. RESULTS: Compared with women with BMI 18.5 to <25 kg/m(2) , the odds ratio was 5.73 (95% CI 4.28-7.68) for women with a BMI ≥35 kg/m(2) . The odds ratios were 1.10 (95% CI 1.09-1.12) and 1.63 (95% CI 1.52-1.75) respectively for an increment of BMI of 1 and 5 units. The relation was stronger in never-users of oral contraceptives (OR 3.35, 95% CI 2.78-4.03, for BMI ≥30 versus <25 kg/m(2) ) than in users (OR 1.22, 95% CI 0.56-2.67), and in women with diabetes (OR 8.10, 95% CI 4.10-16.01, for BMI ≥30 versus <25 kg/m(2) ) than in those without diabetes (OR 2.95, 95% CI 2.44-3.56). The relation was best fitted by a cubic model, although after the exclusion of the 5% upper and lower tails, it was best fitted by a linear model. CONCLUSIONS: The results of this study confirm a role of elevated BMI in the aetiology of endometrial cancer and suggest that the risk in obese women increases in a cubic nonlinear fashion. The relation was stronger in never-users of oral contraceptives and in women with diabetes. TWEETABLE ABSTRACT: Risk of endometrial cancer increases with elevated body weight in a cubic nonlinear fashion.