Airliners cruise at around 11,000 metres, but the cabin isn't kept at ground-level pressure: certification rules set a maximum equivalent to 8,000 feet, about 2,400 metres. At that lower pressure, gases expand by roughly a quarter to a third, which is why your bag of crisps puffs up, your ears pop and your stomach may feel bloated. Every flight is a little trip to the mountains.
Chlorine on its own is fairly gentle. But when it combines with urine, sweat and other grime from swimmers, it forms chloramines, which cause stinging eyes and that classic 'chlorine smell'. A well-kept pool barely smells at all. Shower before you swim and never pee in the water.
Muscle mass slowly shrinks with age, putting independence at risk. But in 1990, a study had nursing home residents aged 86 to 96 train their legs for eight weeks: their strength more than doubled. Muscle responds to training at any age. Getting up from a chair without using your hands is already an exercise.