Adults are advised to do muscle-strengthening exercises twice a week, as well as aerobic exercise, to help them stay active for longer, under new guidance from the UK's top doctors.
For the first time, it includes advice on safe activity levels for pregnant women and new mums.
Dance, bowls or Tai Chi are advised for over-65s to reduce falls in old age.
Physical activity protects against obesity, type 2 diabetes, heart disease and depression, the advice says.
The new guidelines on physical activity have been produced by the UK's chief medical officers and updated to reflect the latest scientific evidence. Their message is that any activity is better than none, and more is even better.
Prof Dame Sally Davies, England's chief medical officer, said most children and adults in the UK are not active enough.
"We need more active travel, we need people to get off the bus or the tube a stop early. We need people to climb stairs instead of getting in a lift. We need to be more active."
The guidelines recommend that adults build strength and balance to help stave off the natural decline in muscle mass and bone density that starts around the age of 50.
Tim Hollingsworth, from Sport England, said it was great to see the strength and balance exercises on a similar footing to cardiovascular exercise.
"The beauty of it is there are many ways to build strength and balance, whether it's at home, at the gym or through sport.
"Resistance training, circuit training, racquet sports and yoga are all great, for example, for improving muscle function, bone health and balance."
Dr Max Davie, from the Royal College of Paediatrics and Child Health, said families must try to build exercise into daily routines by walking or cycling to school, for example.
"We know that by doing so, it can have major mental and physical health benefits for their growing child both now and in the future," he said.