Previous studies, monitoring walking speed and jumping height, have suggested that HRT reduces the impacts of age-related decline in muscle mass and strength.
This new study is the first to explore these effects at cellular and molecular levels.
The research team observed pairs of postmenopausal identical twins - of whom only one of each pair was receiving HRT - in order to rule out genetic differences, and then performed close examination of muscle biopsies taken from them.
"We found that even though individual muscle fibres did not change in size, the muscles of HRT users showed greater strength by generating a higher maximum force compared to non-HRT users. It is thought that using HRT, at least in part, reduces modifications of muscle contractile proteins that are linked to ageing," Dr Lars Larsson, from Uppsala University Hospital Sweden, who led the study, said.
"HRT is also associated with a more efficient organisation of myonuclei, which are essential components for muscle fibre function. In HRT users, the different myonuclei arrangement optimises cellular level protein transport that leads to improved muscle function," said Larsson.
"Fall and fall-related injuries are common among elderly individuals, with significant socioeconomic consequences for individuals and society, and women are affected more than men due to the decrease in female sex hormone production," Larsson said.