Frank Shorter, 1972 winner of the Olympic marathon, said “Hills are speed work in disguise.”  Runners often add hill work to their training, either in the form of hill repeats or running over hilly terrain.  Hills certainly produce a different and more intense workout then flat surfaces.  The question is often asked as to which is better.  To deal with this question we need to look at the differences.

Running or walking up hill is a hard workout, because you are lifting your body weight a few inches with each step.  This raises your heart rate and provides a good aerobic workout.  Stride length is shorter than on flat land, forward speed is slower than the same effort would produce on the flats, and impact is less.  So, the uphill is great for building muscle strength and cardiovascular fitness.

Then comes the downhill.  One way to avoid going down after going up is to run on a treadmill.  Another way to avoid the downhill is what one clever runner did.   She did hill repeats with her coach waiting at the top of a long hill ready to drive her back to the bottom.  Going down produces increased impact, and this is tough on the whole body, especially the knees.  There is a natural tendency to lean back to slow the descent and avoiding falling on your face.  This puts even more impact on the heels.  In a race, the experts advise leaning forward and speeding up.  This is, of course, scary, and dangerous and not for the faint of heart.

Going downhill produces what are called eccentric contractions.  This is when a muscle tries to contract while it is being stretched by an outside force.  A simple example:  lifting and then lowering a heavy weight by bending the elbow.  On the way up, the bicep contract and shorten.  This is the normal muscle contraction and called a concentric contraction.  On the way down, gravity wants to pull that weight down very fast, and the bicep tries to slow the descent but is lengthened as it tries to contract.  Unfortunately, downhill running causes eccentric contractions.  These are primarily in the quads, but in other areas as well.  This is the reason downhills cause a lot of delayed onset muscle soreness.

Going uphill stores potential energy because you have lifted a weight, your body, to a higher elevation.  The rule in physics is that all the potential energy gained by lifting a weight is returned on the way down.  But in running, the downhill does not return nearly as much energy as it took to go up.  On a bike, it is possible to relax and freewheel all the way down.  Here you get a near complete return of energy except for a little taken away by wind resistance and friction.  If you are running on a road where the inclines are very slight, there is a significant return of energy on the downs.  This often makes the decline feel easy, fast, and pleasurable.  On steep hills, there is a lower percentage of return and the down often feels difficult and painful.  One good thing about running on a very slight downhill is that it can be beneficial for learning to improving turnover rate and stride length thus improving speed.

The Comrades race in South Africa is run downhill on even years and uphill on odd years.  It is about 90K or 55 miles, but the two distances are slightly different, so it is difficult to compare times.  However, most who have run both say the down is more difficult.

Bottom line:  Uphill running or walking is a great strength and cardio workout and should be added to training even if your races are on flat surfaces.  The downhill parts can be problematic and should be carried out with care.