Hippocrates once said that exercise is man’s best medicine and he was not wrong. If you need another excuse to hit up the gym, know that a lifetime of regular exercise significantly reduces the effects of aging on the immune system, muscle mass, and cholesterol.

A paper published in the journal Aging Cell measured highly active people aged between 55 and 79 on a range of fitness criteria. While it was previously assumed that aging causes the body to become frail regardless of how many gym hours you put in, the results suggest this is not the case. In fact, the active seniors were able to maintain the body fat, cholesterol levels, and immune system of a young person. In men, regular exercise was also found to keep testosterone levels high and possibly help sidestep the male menopause. 

"We hope these findings prevent the danger that, as a society, we accept that old age and disease are normal bedfellows and that the third age of man is something to be endured and not enjoyed," Niharika Arora Duggal, from the University of Birmingham, said in a statement.

All the active seniors involved in the study were amateur cyclists: the 84 men who took part had to be able to cycle 100 kilometers (62 miles) in 6.5 hours or less and the 41 women 60 kilometers (37 miles) in under 5.5 hours. Their data were compared to those of 75 healthy adults aged 57-80 and 55 healthy adults aged 20-36, none of whom exercised regularly. Smokers, heavy drinkers, and people with high blood pressure and health conditions were immediately excluded from the study so as not to confuse the results.

Most excitingly, perhaps, is the effect of exercise on immunity. It comes down to the thymus, an organ responsible for producing a type of immune cell called the T cell. Scientists expect the thymus to start shrinking and thus produce fewer T cells from the age of 20. Yet, the cyclists maintained the same T-cell count as the youngsters, suggesting regular exercise prevents the immune system from aging.

"Their bodies have been allowed to age optimally, free from the problems usually caused by inactivity. Remove the activity and their health would likely deteriorate," explained Stephen Harridge, Director of the Centre of Human and Aerospace Physiological Sciences at King's College London.

The team hopes this research could prove to be a solution to "the problem that we are living longer but not healthier”, a depressing reality confirmed in a report last year that revealed the expected number of healthy years is not keeping up with advances in life expectancy.

NHS England recommends doing 150 minutes of aerobic exercise a week. Study author Norman Lazarus' advice: "Find an exercise that you enjoy in whatever environment that suits you and make a habit of physical activity. You will reap the rewards in later life by enjoying an independent and productive old age."