Running kit rarely wears out. It gets ruined. Almost always by one of three things, and all three are avoidable.
1. Fabric softener
Softener works by depositing a thin waxy film on fibres. On cotton towels that is what you want. On a synthetic knit it is a disaster, because the film sits across exactly the surface that was doing the work of moving moisture. A tee that has been softened a few times feels fine dry and behaves like a plastic bag wet.
The film also traps the bacteria that cause the smell you were trying to wash out. If you have a top that comes out of the machine clean and starts smelling within ten minutes of putting it on, softener build-up is the most likely reason. Several washes without it will usually strip it back.
Skip the softener entirely on anything synthetic. That is the whole rule.
2. Heat
Elastane is the shortest-lived fibre in most performance garments, and heat is what shortens it. Every hot wash and every hot tumble dry costs a tight or a bra some of its recovery, which is the ability to spring back after being stretched. When a tight goes baggy at the knee after a few months, that is elastane that has lost recovery.
Wash cold. Not warm, cold. Modern detergent is formulated to work at 20 to 30°C and there is nothing on running kit that needs more. Then hang it up. Synthetic knits dry fast enough hanging that the dryer buys you very little.
There is one exception. A water-repellent finish on a shell is reactivated by heat, so a wind shell that has stopped beading benefits from a low tumble dry. That is a specific fabric with a specific finish, not a general rule.
3. The wrong detergent, and too much of it
Biological detergents contain enzymes that break down protein and fat. That is useful on food stains and it is not useful on a garment where the only protein is your own sweat, which comes out fine without them. Enzymes are also hard on wool and on elastic.
The bigger problem is dose. Most people use two or three times what a load needs, and the excess does not rinse out. It stays in the fabric, attracts dirt and holds smell, which produces exactly the outcome that made you add more detergent in the first place. Halve what you currently use on a load of kit and see what happens.
A few things that do help
- Turn tights and leggings inside out. The inside is the side that was against skin.
- Do not leave kit balled up in a bag overnight. Nearly all of the smell problem is that, not the wash.
- Wash socks inside out. The grit that wears through a running sock lives in the pile.
- Do the zips up before washing a shell. An open zip slider chews through a light ripstop in the drum.
- Wash bras with the cups removed, so the cups keep their shape.
What about smell that will not go
A soak in cold water with a cup of white vinegar for an hour before a normal cold wash shifts most of it, and it is far gentler than the sports-specific washes sold for the purpose. If it comes back immediately, go back to the softener question at the top of this page.