There's no doubt that runners who regularly hit the hills get faster. However, you should vary your hill routines throughout the season just as you should vary your training. Because hill work is more stressful, progression is important.
Outdoors vs. Treadmill
I am often asked if running outdoors is more productive than running on the treadmill. The answer is that they both have their place in a good running plan.
The advantage of the treadmill is that you can set your workout parameters. If you're trying to keep your heart rate down during base training, you simply select a pace that keeps your heart rate in that zone.
With hill work, you can vary the pace and incline to create just the right amount of stress for your workout. It may be hard to find a long hill with a steady incline so the treadmill can create just that. You don't want to start off your hill work with too steep of an incline.
With the treadmill, you can increase the incline slightly each week and the resistance is constant. That being said, many athletes find it difficult to stay focused on a treadmill. It's important to include runs on varied terrain and downhill. The treadmill doesn't provide this. As you get closer to your goal race, I recommend trying to duplicate the race course and spend less time on the treadmill.
Hill Progression
The most important aspect of base training is staying aerobic and keeping your heart rate down. Hills will obviously drive your heart rate up but that doesn't mean you should eliminate them in base training. In fact, this is the best time to build a strength for the season. As the season progresses, intensity should as well. The following workouts are in order of progression throughout the season. It's important to follow this progression or overtraining and/or injury could result.
Hill climbing: Walk to run faster? Correct; I start even my fastest and most seasoned athletes out with hill walking. Walking on a steep incline can get your heart rate up just as much or more than a slow run and there is less impact and eccentric load. It is a great way to strengthen the gluteals, hamstrings and calf muscles. Hill walking is performed during transition phase and early base training. I also recommend trail hiking.
Base/endurance hill intervals: This workout is a bit more structured. I start the athlete out at a low base aerobic level and increase to a higher aerobic level towards the end of base and into general preparation periods. I prescribe intervals of five to 20 minutes with five to 10 minutes of recovery between efforts, up to two times a week. Pace and incline must be adjusted to keep heart rate in the zone. This may mean running very slow, but you will feel resistance on your legs. This is a good workout for the treadmill, but it can definitely be performed outdoors with a little planning.
Steady hill intervals: We take the top of your aerobic zone and hold a narrow heart rate range. Because this workout is more precise, it is easier to perform on the treadmill. Again, I prescribe intervals of five to 20 minutes with five to 10 minutes of recovery between efforts, up to two times a week.
Fartlek hills: This is one of my favorite workouts. On a hilly course, you will push hard on the uphill sections and run a relaxed pace on the downhill. This is an unstructured workout and is best performed outdoors. Fartlek hills build strength, power and aerobic capacity.
Tempo hill intervals: These hill intervals are performed at a much faster pace. Your heart rate will be slightly below threshold or your 5k race pace. I prescribe intervals of five to 15 minutes with at least 10 minutes of recovery between intervals. Perform this workout no more than once a week.
Hill bounds: Bounds are a springing motion with plenty of vertical power. Picture leaping from point to point with a long stride as you climb a hill. You want to work on producing quick, explosive power. I prescribe hill bounds of 50-75 meters. Recovery is a slow walk back down the hill. Usually four to eight of these will be enough. Perform this workout no more than once a week.
Hill sprints: Now we're talking ... This is hill speed work with no heart rate prescribed. On a hill of approximately 100 meters, start off at a moderate pace and build to a sprint. In the last 10 seconds, sprint as hard as you can to the top of the hill. I prescribe this workout no more than twice a month in race preparation period. I may prescribe several sets of three to four hill sprints. Recovery between sets is 10-15 minutes of easy running. Recovery between efforts is a slow walk back down the hill.
Hill strides: These are a technique drill. A lot of runners slow their stride rate and lengthen their stride as they attempt to power up a hill. The exact opposite should take place. Count your strides going uphill. Your stride rate should be around 30 right foot strides in 20 seconds. Work on a short, fast, efficient uphill stride. You should perform these in all periods throughout the season.
Don't forget that hill work is more stressful than running the flats. It's important to increase incline gradually and to let your body adapt. If you experience any calf or Achilles area pain, stop immediately and take a few days off. Don't resume training until you are pain-free. Hill work will help prevent injury and strengthen your tendons, joints and ligaments, but only if the stress load isn't too high. Fitness can't be rushed and hill work is no exception.