Physical Aspects of Trail and Fell Running

Keven Shevels

This article is reproduced from the booklet “An Introduction to Trail and Fell Running” with the permission of Trailguides Limited. Further information on the booklet can be found at:

Not many people from a non-running background make the sudden decision to try trail and fell running. It is a relatively safe assumption that those who are either contemplating trying or are new to off-road running have come from one of the other running disciplines and in all probability road running. As such they will be aware of the physical demands that running places on the participant. But what of the additional physical requirements over and above what would be the norm for, say, the average road runner. This section looks at these additional demands.

Running style:

The classic endurance running style is all about running as fast as possible while using the least amount of energy. This tends to give a running style with the arms close to the side and moving backwards and forwards, slightly crossing the body. At the same time the body is held vertical with a slight lean forwards. Stride length is not too long and the thigh is not lifted as high as in fast paced running with the foot skimming just above the running surface. When running off- road this classic style still holds true as being the most energy efficient method of running. However there are sections in every off-road race where this energy efficient style has to be modified and changed. In certain circumstances the most economical running style is not the most practical or efficient. Practical examples of this are:

  1. Running down hill where the arms are used for balance and where the stride length and head and body position may be altered.
  2. Running uphill where there is a greater lean forward into the hill and arms will pump more vigorously to help power legs.
  3. Running across uneven terrain where high vegetation may force the runner to adopt a higher than normal knee lift.
  4. Running across uneven terrain where the runner may be constantly having to change stride length, unlike the road runner who gets into a constantly repeating rhythm.

The off-road runner may be constantly changing running pattern to meet changing ground conditions. In these circumstances it makes logical sense to adapt their training schedule to include exercises that will improve the ability to change running pattern both quickly and constantly.

Stable and Unstable Ground

In this guide the terms stable and unstable ground are often mentioned.

In order to make the most effective use of his running stride the runner needs to place his/her foot on a hard level surface. This will enable them to make the most use of their energy and power to push themselves away from the ground on the take-off stage off the stride. The classic examples of a hard level running surface are athletics tracks and roads. These are considered to be stable surfaces.

In the off-road world nothing is as stable as these two although such surfaces as forest roads and well-made vehicle tracks can be considered as stable. Any other ground can be considered as being unstable to various degrees because it does not allow the runner to make the maximum use of his/her energy and power.

This may be due to the ground being soft and absorbing energy or being uneven and/or loose and not allowing the runner to push-off in a straight line or it could be any combination of the two. Because of this, running on unstable ground is naturally slower than on stable ground.

All off-road running is classed as running on unstable ground. For the off-road runner, the choice is finding the least unstable ground to run over in order to make the most effective use of his/her running action.


Running off-road places certain stresses on the body over and above those encountered during normal running. Starting at the bottom we’ll look at the various muscle groups in turn and establish what these stresses are.


Starting right at the bottom of the leg, the ankle. The optimum running position has the foot and ankle pushing away from the ground after landing. This push is best done in a straight line with the foot and ankle level and providing a stable support for the push. In road and track running the running surface is relatively level and stable and therefore no great problem for pushing off. However with off-road running the foot will probably land on an uneven surface and as it lands will roll in one direction or another. In order to control this roll and prevent the body over-balancing resulting in a fall, the ankle muscles will compensate to bring the ankle back into a level position during push-off to maintain the straight ahead direction of travel. This compensation obviously works the ankle muscles and ligaments a lot more than just normal running. Stiff and sore ankles are quite often the result of running over rough, uneven ground.

The ankles can also suffer during downhill running. The effect of gravity as you run downhill is increased compared to flat running because of the angle of descent, the leg falls a little bit further than normal on each stride. This means that the ankle suffers a little bit more stress and impact shock than during normal running.

Buttock muscles

The buttock is comprised of three muscles:

  1. Large.
  2. Intermediate.
  3. Small.

These muscles are used a lot more during off-road running compared to road running. The large buttock muscle powers the backward drive of the leg and this is heavily used when running uphill. The intermediate and the small buttock muscles stabilise the hip and restrain the upper body preventing it folding inwards on every stride. These are heavily used while running down hill as gravity and the angle of the descent combine to give increased stride length.

Groin muscles

The groin muscle or to be more precise the adductors work quite powerfully as the foot leaves the ground and starts to swing forward. During this swing, the leg rotates outwards in relation to the hip. The adductors then come into play and swing the leg back towards the midline of the body. Additional pressure is placed on the adductors when side stepping or suddenly changing direction. Occurrences that do not happen during road running but which are common movements when running off-road.

Thigh muscles

The thigh muscles or quadriceps (quads) are used during running to prevent excessive knee flexion. When running, gravity pulls the knee downwards on every foot strike, this is known as knee flexion. Due to the angle of descent, the quads can be put under considerable pressure when running downhill. As the proportion of downhill running is that much higher during trail and fell compared to road running the stresses that the quads are placed under is also considerably higher.

Calf muscles

The calf muscles are very important for running. They bend both the knee and the ankles so that the body can be raised on to its toes during the push-off stage of the running action. Additional strain can be placed in these through coping with running on uneven terrain and up and down slopes.

Trunk and upper body muscles

In the normal running action the trunk remains almost erect with only a slight forward lean, while the arms assist the running action by balancing the rhythm of the legs. When running off-road this all changes. The trunk muscles, both back and abdominal, are used more often as there is a much higher movement of the body compared to road running. This is due to the balancing action from having to run across uneven ground and particularly due to the fact that the additional stresses placed on the other muscle groups ultimately all run through the core of the body, the trunk. Again the arms and shoulders have a much higher rate of movement than compared to road running. This ranges from being pumped backwards and forwards to help power uphill movement to being carried in the outstretched position to aid balance while descending.

Energy consumption:

One of the most heard comments from beginners to off-road running is how tired they feel after a race. More tired than after a corresponding road run. A large chunk of this is down to the increased energy demands that is placed on the body by off-road running compared to running on the road or track, but what causes this extra need for energy.

The answer to this is down to three factors:

  1. As part of the motion of running the body lands on one foot and then immediately pushes away again to take-off for the next stride. This push and take-off requires an explosive force, which in turn requires energy to power it. Part of the energy comes from the bounce-back effect of the foot hitting the ground. The harder the surface, the stronger this bounce-back effect. Correspondingly the softer the surface the weaker the bounce-back. This happens at the moment the foot impacts the ground. A softer surface will absorb more of the impact force than a harder one resulting in a weaker bounce-back. The weaker bounce-back means that the runner has to expend more of their energy to lift their legs. This may not seem much but consider how many times the runner lifts the legs during the course of a run and it soon mounts up. As a practical example of this principle take a rubber ball and bounce it on a concrete floor and then bounce it on a grass field. On which surface does the ball bounce higher and farther ??
  2. By its very nature running off-road crosses more unstable ground than roads or track running. In order to keep the body in an upright position there needs to be some compensating use of other muscle groups. It is often not fully understood by runners that there is an increased demand of the core muscle groups such as the abdominal and upper and lower back. In addition to this there is an increased usage of the arm and shoulder muscles for both balance and to power up hill running. In short this means that you are using more muscle groups during the activity of off-road running and this usage requires energy.
  3. Be it trail or fell there is nearly always more hills than there are in a corresponding road run. Uphill running requires more energy than level running. In reality the concept of what you lose on the uphills, you’ll get back on the downhills does not apply. When compared to running on the level, running up an incline of 6% [6 metres of vertical climb per hundred metres of level distance] will use 35% more energy. On the other side running downhill on the same slope only reduces the effort by 25%, a mismatch of 9% of the runners energy consumption. As you can see the hillier the course the higher the cost in energy expenditure.

Ok, so off-road uses more energy but what effect does that have on training and competition. Keeping things fairly simple, the primary fuel for all exercise is carbohydrates. This is converted into Adenosine Triphosphate or ATP, which is the actual fuel for the explosive muscle contraction, which powers all movement. Once the body store of carbohydrate is exhausted the body then changes fuel source to run on fat reserves, however fat is a much less efficient fuel source than carbohydrate and can result in a significant difference in performance levels. For normal running the average runner holds enough carbohydrates in their body for 90 minutes of exercise. As we’ve seen above off-road running has a higher energy consumption than normal running. Therefore the carbohydrate reserve will be consumed before the 90 minutes is reached. The body will start switching to using fat reserves a lot sooner than on a corresponding road run. The rougher and more physically demanding the course, the higher the energy usage and the sooner carbohydrate reserves are depleted. Off-road running is therefore much more endurance based than even regular long distance running and needs to be trained for as such. This training may mean a higher proportion of endurance ( long runs ) sessions and may also include practicing replenishing energy stores while on the run.

Slow running and walking:

One of the fundamental criteria of all endurance running is getting the best performance out of the bodies limited energy stores. The most effective way of doing this is even paced running. Top quality runners are capable of churning out times where the mile splits are within seconds of each other. Unfortunately even paced running is totally dependant upon having an even running course and surface in front of you. If there is a large hill to go up or come down or a rough running surface to cross then it becomes very difficult to maintain an even pace. By their very nature off-road courses will always contain elements that will force the runner to constantly change pace. Each course will have sections where the runner will be able to run fast and where they will be forced slow the pace and maybe even walk. It then becomes important to factor the ability to pace change into the runners training.

To anybody participating in road running there is a self-imposed mental disgrace about walking. This is probably due to the fact that a road race is more accessible to spectators and self-pride prevents any walking in front of them. With off-road running there is a different attitude. In both trail and, especially, fell races there maybe sections of the route where it is just too inefficient to attempt to run and it makes more sense to walk. This may be down to the nature of the ground being crossed such as overgrown vegetation i.e. deep heather or more likely down to the fact that the hill is just too long and steep to run up.

Load carrying:

Although not usual in competition, there may still be a requirement for the road runner to carry drinks or waterproofs during training. With the off-road runner there is a definite requirement to carry drinks and equipment during both training and competition. This additional load will vary depending on the event and the equipment required. However carrying additional weight of any size will impose higher physical demands upon the runner. Load carrying will effect the running style, endurance capacity, energy consumption, running speed and strength requirements.


As with all runners a regular general stretching routine or even possibly a yoga session will provide enough flexibility for the off-road runner. However there are three areas that do warrant extra attention and need to be included in any stretching routine.

Upper body stretches.

As we have seen the trunk, back and shoulders play a more prominent part in off-road running. It is surprising how many runners neglect to include stretching exercises for these areas into their routine. This needs to be done.


Most runners do include quad stretching exercises into their routine. However, as explained previously, off-road running makes a considerably heavier demand on the quads than other forms of running. This gives a greater importance to these exercises.


The groin area or to be specific the adductor muscles play a major part in all running activities. However both trail and fell running place a particular stress on them due to side-stepping or sudden changes in direction when competing off-road. This can over-exert these muscles and give considerable discomfort in the groin area, often called a groin strain. This over-exertion is mainly caused by an inflexibility of these muscles. Incorporating specific exercises into your stretching routine will help act as a preventative against any possible injuries.

This article is reproduced from the booklet “An Introduction to Trail and Fell Running” with the permission of Trailguides Limited. Further information on the booklet can be found at: