In a healthy adult, it takes about five hours on average to clear half the caffeine you consume, though this varies a lot from person to person. So half of a 4 p.m. coffee is still active around 9 p.m. One study found that a strong dose taken even six hours before bed could cut sleep by more than an hour.
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.