If you are like many runners, you have probably wondered whether you could improve your biomechanics – and whether that improvement might upgrade your performances and decrease your risk of injury.

Before I address whether that is possible, let’s take note of the fact that biomechanics is the study of the forces which act on the body during running, especially with regards to the muscles and skeletal system.  Kinetics is a branch of biomechanics which studies the forces and motions which are characteristic of the running gait.  Kinematics focuses only on the motions of the body during running without worrying about the forces, including the positioning of the joints and the movements of the legs, arms, trunk, and head.

In theory, there is an optimal way to move while running, a best-possible way to position the joints and create propulsive forces as you scamper along.  This could be viewed from a performance-improvement or injury prevention standpoint.  In the former situation, this would mean positioning the joints and creating forces in ways which maximize speed.  In the latter case, the idea would be that there is a specific way of running which minimizes stresses placed on the bones, connective tissues, and muscles of your legs and thus keeps running injuries at bay.

Exercise scientists have searched for such optima among elite runners, thinking that the very best runners would have naturally developed biomechanical patterns which promote the highest-possible running velocities and simultaneously block injuries.  Instead of finding predictable kinetics among the elites, however, the scientists have discovered wide variation in biomechanical variables.

Take maximum knee flexion during the swing phase of the gait cycle, for example.  Some elites flex their knees a lot during swing, reaching angles as great at 140 degrees, but others only flex to 109 degrees (the angle of the knee during running is defined as the angle between the actual position of the shin and an imaginary line drawn to indicate the position that the shin would occupy if the leg were perfectly straight; knee angle is zero when the leg is perfectly straight).  This kind of variation is found when almost all other biomechanical variables are studied.

In other words, scientific research suggests that running biomechanics are highly personal and probably depend on such individual characteristics as skeletal structure, flexibility, joint stiffness, muscle length, overall muscular strength, and neural coordination of gait.  There is not an optimal biomechanical pattern which can be applied to you – which can be used to change your individual biomechanics and thus alter your performances and risk of injury in a predictable way.

As a result, no coach or exercise scientist can make specific biomechanical recommendations to an individual runner with the assurance that the advised changes will work.  There is no optimal thigh angle for the various stages of stance or swing, for example, which has been identified as being better for performance or injury prevention.  There is no optimal degree of ankle dorsi-flexion during stance.  There is no optimal duration of the stance phase.  And so on.

What makes more sense is that increased activity and force production by the muscles of running, if they are produced at the correct times during the gait cycle, should improve running performances and might also provide a protective effect and lower the risk of injury.  This is probably why strength training for running has been linked with improved performances and a reduced rate of injury.  Thus, a sensible approach for runners to follow would be to strengthen the various movements involved in gait in a running-specific way, instead of artificially tinkering with movement patterns.

The perils of making recommendations about biomechanics are illustrated by a recent study from Belgium in which 84 individuals were monitored for knee (patello-femoral) pain during a six-week training period.  Subjects who were most likely to develop knee discomfort tended to land more toward the outsides of their heels during gait, compared with injury free individuals – and to roll toward the outsides of their feet during stance.

Now, we could tell these people to change their biomechanics in hopes of eliminating the knee injuries.  We could instruct them to land more toward the centers of their heels and to focus on not letting their feet roll toward the outside during stance.  We could get them to run more like the pain-free runners.

But it probably wouldn’t work.  The fundamental problem with these subjects was most likely a lack of running-specific strength, not the pronation per se.  The strength inadequacy let the ankles pronate to a greater extent, and this pronation might have put extra stress “up the chain” in the knees.  If we got these runners to land squarely on the middles of their heels and to focus on avoiding pronation, the lack of strength associated with their new biomechanical patterns might simply produce a new kind of injury.

But if you’re going to strengthen yourself, how should you do it?  The key is to make sure your strengthening movement mimics some part of the gait cycle of running.  Otherwise, the gains in strength will not transfer well to running, and you’ll end up stronger in the gym but not out on the roads.

Take hamstring strengthening, for example (a good thing to take, since hamstring injuries are so common among runners).  Many runners think that the key function of the hamstrings during running is to contract and extend the hip while the foot is on the ground, thus providing forward propulsive force.

In reality, the hamstrings are most-active during the swing phase of gait, when the foot is off the ground and the leg is swinging forward, getting ready for the next contact with the ground.

This is an eccentric action of the hams, one in which these key muscles are being stretched out while they produce force to control the forward swing of the leg, preventing this forward swing from getting out of control.

So here’s the picture: The hams are most active during running when the foot is off the ground and the leg is swinging forward.  Does this fact make it sound like hamstring curls, a very popular gym exercise, would be the best hamstring-strengthening drill?  To perform hamstring curls, a runner usually lies prone on a bench and uses the hamstrings to contract concentrically and flex the knee, with resistance provided by a bar positioned against the ankle.  Well, at least the foot is off the ground!

Even the classic exercise for the hamstrings – lunges - is not optimal, since it is performed in a way which puts most stress on the hams while the foot is in stance, not swing.

A much better hamstring-strengthening exercise for runners, one which includes hamstring activation towards the end of swing, would be bicycle leg swings.  To carry these out properly,  you stand with your usual running-tall alignment, with weight fully supported on your left leg (initially, the right hand may be placed on a wall or other support structure to maintain balance).  You begin by flexing your right hip and raising the right knee up to waist height (the right thigh should be parallel with the ground); as this is done, the right knee should be flexed to 90 degrees or more.  Once the thigh is parallel to the ground, you begin to extend the right knee (by swinging the lower part of the right leg forward, unflexing the knee) until the knee is nearly fully extended (the leg is nearly straight), with the right thigh still parallel to the ground.

As your right knee nears full extension, your right thigh drops downwards and backwards (scraping the right foot on the floor/ground as the leg moves back, something like rubbing mud off the bottom of the shoe) until the entire thigh and leg are extended behind the body (as if you were following through on a running stride).  Your right knee should be near full extension (the leg should be basically straight) until it reaches the peak of the backswing.  As your right hip nears full extension (as you approach the end of the backswing), you raise the right heel by bending your right knee; the heel should move closely towards the buttocks as this is done.  As this happens, your right knee is moved forward until it returns to the appropriate position in front of the body, with the right thigh parallel to the ground again.  This entire sequence of actions is repeated in a smooth manner so that the hip and leg move through a continuous arc without stopping or pausing.

Once you are able to coordinate the movement, the swings should be performed at a cadence of about 12 swings every 10 seconds or so (slightly faster than one swing per second).  To enhance the effectiveness of the exercise, a stretch cord should be attached to the “swing” (non-support) ankle at one end and a firm post, table leg, fence, railing, or other structure (at roughly knee height) at the other end.  You stand facing the post, table leg, fence, or railing, with enough distance between yourself and the structure so that the stretch cord significantly accelerates your leg forward during the forward-swing phase of the exercise (this forces the hamstrings to create a braking force during swing, exactly as they do during actual running).  This enhanced forward acceleration created by the stretch cord puts the hamstrings under considerable stress (as they try to brake the frontward movement of the leg) and is ultimately be very strengthening for the hamstrings in a running-specific way.

The hips should be kept fairly level as the exercise is performed.  Naturally, once you complete the required number of reps with the left leg as the support leg, you should change over to standing on the right foot while the left leg performs the swings.  Important things to avoid include too little tension on the stretch band (creating a situation in which the band won’t accelerate the leg forward properly), not getting good hip extension on “back swing,” a lack of explosive forward thigh movement, and a wobbling of the body as the swings are performed.  Begin with about 20 bicycle swings per leg, work up to three sets of 60, and gradually increase the resistance (and thus snap-back power) of the stretch cord.

It’s very likely that this exercise will help you avoid hamstring injuries far more than any biomechanical adjustments which could be suggested for you.