by Shawn McDonald
Running biomechanics involves the study of the motions and timing involved in the running stride. Research has been conducted in the past to detail joint flexions, muscle contractions, the role of arm swing in running economy, as well as stride rates and length among other topics. In the column this month, we will examine the specifi cs of the running stride and what good running form looks like, and detail a few drills you can use to improve your running biomechanics. The winter and early spring are a great time to clean up your mechanics and get ‘back to the basics’.
Good form involves running with an upright posture. Aim to keep the center of your head, shoulders, hips, and foot-striking ankle in a vertical line. Avoid leaning forward from the waist, which often happens when runners get fatigued late in long races or training runs. A forward or backward lean causes stress on postural muscles in the abdomen and back, which raises your energy cost. During the foot strike part of the stride, the leg should be slightly flexed such that the knee is just in front of the head-shoulder-ankle vertical line. Aim to keep your foot strike directly under or slightly in front (by an inch or two) of your center of gravity by landing just behind the ball of your foot, not on the heel. If you land on your heels, you are over-striding (see stride frequency section and drills below), in effect braking and losing momentum on each stride, lowering your running effi ciency.
Throughout the stride, your arms should be at your sides, with a loose 90-degree angle formed at the elbows. Move your arms in a natural, relaxed pendulum motion from the shoulders, forward and back. Your hands should come up to a few inches below your shoulders at the highest part of the arm swing, and to a couple of inches above your hips at the low point. Do not move your shoulders from side to side and don’t allow your hands to cross the centerline of your body on the forward arm swing. Such side to side motion wastes energy and can throw you off balance, particularly if running on uneven trail. Make sure your arms, shoulders, and hands are relaxed throughout each stride and keep your hands slightly cupped. After foot strike, allow your heel to drop and contact the ground, then push off with the ball of your foot. After push-off, both of your feet will be off the ground, the part of the stride cycle called forward recovery.
When running downhill, lean forward slightly with your whole body so as to maintain the 90-degree alignment of your head-shoulderships- ankle with the ground. For uphill running, lean slightly into the hill with your whole body so as to form a stable platform with which to push yourself up the hill using your quadriceps and calf muscles. Avoid leaning over from the waist, which interferes with deep breathing and can cause tension in the midsection and shoulders.
The running stride or cycle consists of two periods, called the support phase and the forward recovery phase. During the support phase, one foot is in contact with the ground. In the forward recovery phase, the trailing foot has left the ground and moves up, forward, and then down to its next contact with the ground. (The walking stride differs from the running stride in that one foot is always in contact with the ground.) Each foot is in contact with the ground for just over a quarter of a second for most stride frequencies. Actions that take place during the support phase include: knee fl exion, tibia rotation, pronation of the subtalar joint in the foot, ankle fl exion, supination of the subtalar joint, locking of the midtarsal joint, inversion of the calcaneus (heel bone), hip extension, and knee extension. Motions involved in the recovery phase include hip fl exion, pelvis rotation, knee flexion, knee extension, hamstring contraction, and forward movement of the foot and leg.
Proper mechanics involve moving the body forward, with a minimum of vertical motion of the body trunk as a whole. Keep as a mental picture the way in which the top of the head of Alberto Salazar stayed parallel to the top of the wall of the Queensborough Bridge during the New York City marathon. The foot at each foot strike should be straight and in line with the direction of forward motion. If the feet are turned outwards the distance covered by each stride is reduced and more stress occurs on the lower legs and knees (Williams, 1990).
Considering that all these processes occur in a span of about 0.7 seconds (at a stride frequency of 180), it can be diffi cult to know if the mechanics of your own running stride are ‘normal’ or effi cient. Videotaping can be used to examine the specifi cs of your stride and any changes that occur over a period of training. If you have access to a physiology lab, you could have measurements made of your oxygen use at different running speeds (see Lore of Running, pp. 28-29, and Figure 2.4). Then after doing form drills for several weeks, again have physiological tests performed to see if your oxygen costs at several running speeds (‘effi ciency’ or ‘economy’) have improved.
The stride frequency of a runner is the number of times per minute that one of their legs completes a stride cycle. The stride length is the distance between successive foot strikes of the same foot. Stride frequency and stride length increase as speed increases (Cavanagh and Kram, 1990). There are a number of variables amongst runners that affect which combination of stride length and frequency they employ for a particular running velocity. These include leg length, leg muscle development, hip fl exibility, degree of prior training (both in terms of volume and intensity), and state of fatigue (Cavanagh and Kram, 1990). Most runners develop stride lengths and frequencies that are most effi cient for their bodies via trial and error over the many hours of training. Also consider that shortening or lengthening this optimum stride length can raise the energy and oxygen costs of running. In particular, under-striding uses too many running cycles to cover a particular distance per minute, while over-striding causes deceleration, as leg muscles in effect break the momentum of the body to allow it to catch up with the planted foot.
Most runners will have stride frequencies in the range of 160-180 per minute. This means that each foot strikes the ground about 80-90 times per minute. A runner moving at six minutes per mile with a stride frequency of 180 would have a stride length of ten feet. Remem half of this distance, or about five feet. A runner covering ground at nine minutes per mile using a stride frequency of 160 would have a stride length of 7.3 feet. To determine your stride frequency, count the number of times your left foot hits the ground in one minute, and then multiply by two. Try running at various speeds over the course of a training run, while counting your foot strikes periodically, to get an idea of how your stride frequency and stride length change as your velocity changes. To change your stride frequency at a given velocity is not easy and will take lots of practice. Try doing the quick stride drill below a couple of times a week. The drill work might be worth it if your current stride frequency is outside of the above range.
Physiological benefits of good form
Using proper body form and running mechanics lead to better efficiency and economy for a given fitness level. For example, consider two runners with the same VO2 max. One runner has a shuffle stride, smooth arm swing, and appropriate stride frequency. The other runner has a low stride frequency, leans over substantially from the waist, and has a high knee lift and ankle kick. In a race, the first runner will beat out the second, less efficient runner. By using a more economical body posture and running mechanics, the first runner is getting more bang for their aerobic buck, even though both runners might be moving along at the same percentage of their VO2 max during the race.
A runner with the same VO2 max but better economy will also burn less fuel during a race, which is important for races of marathon length or greater. The efficient runner will become less fatigued late in the race, helping them to finish faster. An efficient, well-balanced running stride also puts less stress on running muscles and major joints, leading to fewer injuries over the many months a runner trains to prepare for an ultra. The difference between inefficient and economical mechanics can sometimes be heard. A runner with a rough stride will land harshly with their feet slapping the ground. An economical runner will glide along, landing softly on each foot while using a rhythmic, powerful arm swing to aid leg motions. Runners who overstride land more on their heels, which can wear down running shoes more quickly.
A runner may be more or less efficient when running uphill or downhill compared with perfectly flat terrain (Gregor, 1970). Economy changes in this case may be due to factors such as doing the bulk of training on hills (or flats), body weight distribution, limb lengths, and using a stride that is not optimum for the terrain. Using a weak arm swing when running uphill or an arm swing that is too vigorous (especially if the arms leave your sides and cross over the trunk centerline of your body) on downhills can lead to lower running economy.
Drills to improve form and mechanics
In the pose drill developed by Romanov (2001), the body is in a relaxed S shape while standing on one leg with the other leg in the middle of the recovery phase, with the ankle at mid-calf level. While in the pose, check that your head, shoulder, hip, and ankle are in vertical alignment and that your weight is on the ball of your foot, with your heel slightly lifted off the ground. The position of the heel and ball of the foot at contact are important, as this allows the ankle and Achilles tendon to act as springs to store kinetic energy as the body falls towards the ground with each stride. Your contact point with the ground should be close to your center of mass, underneath the trunk axis of your body. Your knee, ankle, and hip should be slightly flexed while in support. Your upper body should be relaxed with your arms hanging naturally, and about a 90-degree angle formed by each elbow. Check each of these pose features using a side-view mirror or have a friend or coach help you. Practice holding the pose standing on your left leg for ten seconds. Then break the pose and walk around for a few seconds. Then resume the pose and hold again, and repeat several times. Then switch the support leg, repeating the pose, hold, and break process several times.
A drill called the Pony (Romanov) is used to practice exchanges of support between your legs during the running cycle. Begin in the running pose, with the non-support ankle off the ground a few inches. Lift the support ankle vertically while transferring your body weight to the opposite leg, which is falling to the ground and relaxed. Start each exchange by lifting the support leg (ankle), not by pushing down on the non-support leg. Focus on lifting the ankle vertically, not forwards or backwards. The ball of each foot should contact the ground first and weight should be shifted without causing muscle tension in the non-support leg, until that leg starts to bear weight. An advanced form of this drill can be done by eliminating pauses between each exchange of support, by increasing the amount of ankle lift, and by adding body lean (see the Romanov article for one leg hopping and body leading drills).
In the foot-tapping drill (Romanov), hold the non-supporting leg with the ankle elevated. Then allow this leg to drop to the ground by relaxing all the muscles in this leg. Remain standing on the support leg and allow the foot of the non-support leg to tap the ground. As soon as you tap, fire the hamstring on this leg to elevate it. Seek to keep the quadriceps of the non-support leg relaxed during the whole motion. Tap with one leg for perhaps a minute, then take a short break, and repeat by tapping with the other side. This drill develops your ability to make quick, balanced exchanges of support by minimizing the effort needed to lift your heels.
Begin the heel kick drill (Morris) by using a slow jog. Use a short stride and bounce on your toes. Raise your heels as high as possible behind your body. Try to get your heels to bounce off your buttocks. Most of the movement should be done using your lower legs with little upper leg motion. You should move forward slowly, covering 30 to 50 meters. Repeat this distance a few times. This drill helps you improve range of motion in your lower legs while developing a better sense of the motion and location of your ankles during the running cycle. The quick stride drill (Morris) is useful if you want to increase the quickness of your foot strike or increase your stride frequency. Start out at a slow jog. Increase your stride rate so that you take as many strides in 25 meters distance as possible. Focus on foot speed and quickness. Repeat several times.
Developing an economical running stride is a matter of combining good running form and proper biomechanics of the legs and arms. Benefits of form work include improved balance and coordination while running on all surfaces, lower impact forces on the body (fewer injuries), and faster race times. Unnecessary movements will be eliminated and quickness will be added to your stride. Form drills are a great way to retrain your nervous system to complete the correct sequence of motions with good timing. The cooler months of the year are a fine time to add form drills to your routine, as many runners are completing lower volume/intensity training.
Hughes, D. “The art of running: a biomechanical look at efficiency” http://www.texastrack. com/coaching_article_5.htm
Dallam, G. and Romanov, N. “Developing Improved Running Mechanics” article in 2001 USA Triathlon newsletter
Morris, R. “Running drills” http://www.runningplanet.com/training/running-drills
Noakes, T. Lore of Running (1991) Leisure Press, Champaign, IL (pp. 18-38)
Cavanagh, P. and Kram, R. (1990) Biomechanics of Distance Running (pp. 35-63)