A workout method that alternates short bursts of vigorous exercise with brief recovery periods could be the “optimal exercise” for losing body fat while retaining muscles in older adults, scientists reveal in a new study.

Retaining muscles becomes a challenge with ageing, even as losing muscle mass increases the risk of several metabolic conditions like diabetes and heart disease.

Doctors recommend that older adults routinely engage in physical activity to prevent body composition changes and the consequent risk of disease and death.

However, the evidence for which exercise is best to improve body composition among older adults remains sparse, say researchers from the University of the Sunshine Coast in Australia. This is because most research findings comparing the effectiveness of different forms of exercise are derived from younger populations, which do not represent the metabolic and hormonal profiles of older adults, they say.

Now, a new study has compared the effect of different intensities of exercise on the body composition of over 120 seniors from the Greater Brisbane region in Australia.

“We found that high, medium and low intensity exercises all led to modest fat loss, but only high-intensity interval training, or HIIT, retained lean muscle,” said Grace Rose, an exercise physiologist from the University of the Sunshine Coast.

“Both high and moderate intensities improved the composition of weight carried around the middle,” said Dr Rose, adding, however, that moderate training also caused a “small decline in lean muscle”.

A general view of equipment as participants take part in a Kobox workout (["Getty Images for KOBOX"])

Their average age was 72 years old, and the mean body mass index was about 26, categorised as normal for people aged over 65.

The participants were randomly categorised into three groups, each completing different intensities of three 45-min supervised treadmill sessions per week for 6 months.

The findings, published in the journal Maturitas, can be useful in managing body composition in seniors, which is implicated in the progression of many chronic diseases as people age.

“High intensity training in this study involved repeated short bursts, or intervals, of very hard exercise – where breathing is heavy and conversation is difficult – alternated with easier recovery periods,” Dr Rose explained.

“Only HIIT had a significant reduction in body fat percentage from baseline to six months,” scientists wrote.

Researchers theorise HIIT could be leading to elevated muscle protein synthesis in older adults.

“HIIT likely works better because it puts more stress on the muscles, giving the body a stronger signal to keep muscle tissue rather than lose it,” she said.

However, scientists caution that further research is needed to confirm these effects and establish clinical recommendations.

“Overall, findings from this study suggest that where possible, healthy older adults should opt for high-intensity interval training over other aerobic intensities for body composition benefits,” they concluded.