Hill training is far more effective at building strength than flat running. Some of the muscles and muscle groups that are strengthened and tightened by hill running include: the calves, the glutes, hip flexors, Achilles tendons and hamstrings. Hill training works the upper body and core muscles, too. It's a full-body workout, requiring the pumping of arms, and even abdominal work that comes as a result of all that up and down repetitive movement.
But muscle efficiency is as important as muscle size and strength, and hill training, especially short hill training regimens, develop explosive, precise muscle strength. Muscle efficiency is a principle of plyometrics, a training program in which muscles are stretched, held and released as a way to create targeted, high-powered muscle action. In short, hill training gives you endurance and provides the extra boost you need to finish strong in races and sprints [source: Frailoi].
Charging a hill without thinking about how to do it first, or researching how to do it first, can be very difficult. Aggressive hill training regimens should only be attempted by experienced distance runners. These exercises require more force, or more accurately, more muscle and cardiovascular conditioning. The quadriceps and connective tissue have to be increased in their capacity gradually. If an exercise calls for two sets of 10 reps, start with just a few. Otherwise you risk tearing a muscle or even damaging a knee or rupturing an Achilles tendon.
Some other things to remember in hill training: Always slow jog after attacking or cresting a hill. It helps the muscles and heart recover. If your heart rate remains elevated after completing the descent, take a rest before you climb another hill [source: Cooper].