A 12-week trial in masters trail runners compared uphill intervals, circuit training and both combined. Only the uphill groups got faster on the trail. Here’s what each one changed, what the sessions looked like, and how to build hills and heavy strength work into a week.

Downhill running is cheap for the heart and lungs but hard on the quads, and unprepared legs fade late in a race. What a single descent does to muscle, which runners coped best, and how to coach and train the descent.