Technical baselayers, compression sleeves, mid-layer breathable tops; trail running is a hobby with a lot of kit on offer. But sometimes - particularly when the weather gets warmer - you can't beat a good ol' t-shirt for running around in. That's not to say tees are bereft are modern technology, though. Resident gear testers Jen & Sim Benson have put a selection through their paces to clue you in on what's what in the world of running t-shirts.