Metabolic flexibility in postmenopausal women: Hormone replacement therapy is associated with higher mitochondrial content, respiratory capacity, and lower total fat mass.

Aim: To investigate effects of hormone replacement therapy in postmenopausal women on factors associated with metabolic flexibility related to whole-body parameters including fat oxidation, resting energy expenditure, body composition and plasma concentrations of fatty acids, glucose, insulin, cortisol, and lipids, and for the mitochondrial level, including mitochondrial content, respiratory capacity, efficiency, and hydrogen peroxide emission.

Methods: 22 postmenopausal women were included. 11 were undergoing estradiol and progestin treatment (HT), and 11 were matched non-treated controls (CONT).

Combined changes in temperature and pH mimicking exercise result in decreased efficiency in muscle mitochondria.

It is well known that exercise efficiency declines at intensities above the lactate threshold, yet the underlying mechanisms are poorly understood. Some have suggested it is due to a decline in mitochondrial efficiency, but this is difficult to examine in vivo. Therefore, the aim of the current study was to examine how changes in temperature and pH, mimicking those that occur during exercise, affect mitochondrial efficiency in skeletal muscle mitochondria.