Fitness fans build their week around training, whether that means an early run before work, a lunchtime gym session or a short workout on the living-room floor. They usually know exactly what kit they rely on, and they tend to wear things out rather than leave them in a drawer. That makes them easier to buy for than it first seems.
Gifts that work are durable and simple to fit into an existing routine. A thick mat for floor work, a set of resistance bands that packs into a bag, a large bottle that survives being dropped on concrete, a gym bag with room for shoes. What tends to miss is clothing in a guessed size, gimmicky gadgets and anything that hints they should be training more. If you are unsure, look at what they carry to the gym or the park and replace whatever looks most worn.