It can be more difficult to remain active during the dark, cold nights of winter. However, the importance of staying active at this time of year has been highlighted by a study, which found that just two weeks of reduced activity can have a major impact on the health of older people.

According to the findings, after just two weeks of less activity - equivalent to around 1,500 steps per day - adults over the age of 60 lose significant amounts of muscle. Furthermore, this coincides with substantial gains in body fat percentage, particularly around the waist.

This can lead to major losses in muscle strength, as well as decreased bone mineral density, which reflects the strength of the bones.

The UK study focused on two groups - one made up of people in their 20s/30s and one made up of people in their 60s. The researchers noted that most research on physical activity looks at extreme forms, such as complete immobilisation, however this is not relevant to the majority of healthy people.

They decided to look at the impact of just two weeks of reduced activity on people.

Before the two-week period of reduced activity, both groups did the same amount of physical activity over a four-day period, so that this could be used for comparison purposes. Participants did over 10,000 steps per day, but did not undertake any vigorous exercise.

The study found that after two weeks of reduced activity, muscle size, muscle strength and bone mass equally reduced in the young and old groups.

Also, both groups gained similar amounts of fat in their muscles and around their waist. However, the older adults had less muscle and more fat to start with. As a result, these changes are likely to have more of a detrimental effect among older people compared with younger adults.

Furthermore, the study also found that cardiorespiratory fitness (CRF) fell significantly among the older participants, but not the younger ones. CRF refers to the efficiency with which oxygen is supplied to muscles during sustained physical activity. Low CRF is usually found in those with poor physical health, and these people are more likely to develop diseases at a younger age.

The study also found that mitochondrial function fell among the older people, but not the younger ones. Mitochondrial function, which is the energy production of our cells, is important for muscle and metabolic health.

The researchers believe that these declines in CRF and mitochondrial function could play an important role in the loss of muscle mass and strength, and gains in muscle and body fat during physical inactivity.

"The severe impact of short-term inactivity on our health is hugely important to communicate to people. If the gym is hard to get to, people should be encouraged to just meet 10,000 steps, as even this can guard against reductions in muscle and bone health, as well as maintaining healthy levels of body fat," commented one of the study's authors, Juliette Norman, of the University of Liverpool.

Details of the findings are to be presented at the UK Physiological Society's conference, Future Physiology 2019, in Liverpool.