Strength and cross-training for runners

Very useful, and it splits into two jobs. The first is staying injury-free: get the key muscle groups strong and train the firing patterns running uses, usually with plyometrics or work that loads you the way running does, so muscles, tendons and ligaments toughen in the right way. The second is economy: lift like a powerlifter, heavy and low-rep, the big lifts like squats and deadlifts. That is where the real running gains sit. When time is tight, do the injury-prevention work first.

Best on a day you have already run hard in the morning, with the heavy lifting in the evening. Same logic as the running: stack the hard work together so the easy days stay genuinely easy. Strength backs off in the taper.

It can be a real help. Cycling and swimming build aerobic fitness without loading your legs the way running does, and too much running load is exactly where injuries creep in. It is one of the best ways to add aerobic work while protecting your legs.

Not at all. It just comes down to managing what you are doing and the total load across the week. Keep the easy things easy and the hard things hard, and a daily habit is fine.