Interestingly, professional runners have frequently been shown to utilize shorter strides than their less accomplished, but nevertheless experienced, counterparts. In a related study of collegiate runners, researchers observed a decrease in running stride lengths from their first to their final year. How do you avoid the impulse to overstride, then?
Stride length
Stride length, both natural and optimal, increases at faster speeds. The key is to discover the way your optimal stride length feels, and it will follow you at any running speed. Renowned exercise physiologist, coach, and Running & FitNews editorial board member Jack Daniels, Ph.D., has observed repeatedly that leg turnover naturally determines stride length.
Focusing runners on reaching 180 steps per minute is an excellent way to move their stride length into the optimal range, without unduly placing all of their focus on running form. For many people, this running cadence is faster than they are used to attaining, but it achieves several noteworthy results.
Daniels writes, "The main problem associated with a slower turnover is that the slower you take steps, the longer the time you spend in the air." This displaces your body mass higher, and leads to a greater ground landing shock. A shorter stride means a lighter stride. Daniels advises that optimal stride rate should feel like you are running "over the ground, not into it."
Try to get the feeling that your legs are part of a wheel that just rolls along ... Try counting the strides of one leg for one minute and see how close you can get to 90. Alternately, you may count arm swings or count steps for 30 seconds and multiply the result by two. So optimal stride length and running turnover are really two sides of the same coin.
Ground-push: Pawback
The corollary to this revelation is the importance of your ground-push. Toward the end of the swing phase of the running gait, once your leg has swung fully forward, forcefully pull it down and back as the foot makes ground contact. Continue this backward pull then push of the leg as you move toward pushoff.
Accentuate the backward push against the ground, and not just a forceful push downward, otherwise you'll bounce up and down rather than propel your body horizontally across the ground. This is called pawback, and it is an important component of running economy.
Swing phase
To discuss yet another alterable factor that influences running economy, it's useful to further examine the swing phase. Following toe-off, contraction of the hamstrings brings the foot up and back toward the buttocks. The bent knee then straightens as the leg swings out ahead of the body's center of mass.
More energy is required to swing a limb with its weight distributed toward the end than concentrated near the joint, which helps explain why studies of optimal running economy have shown that larger upper legs and smaller (and therefore lighter) feet and calve muscles improve efficiency. A more flexed knee during this phase also improves running economy, as the forces required to bring the leg out in front will remain less with a compact leg position.
Quadriceps flexibility
Quadriceps flexibility is a key determinant of knee flexion. To stretch your quads, standing on one leg, keep the thigh of the other perpendicular to the ground and slowly bring your foot up against your buttocks. Over time, the less resistance your quadriceps impose on this action, the less energy you'll have to expend to bend your knee (which reduces the weight you're required to move at the end of your limb during swing phase).
The combination of a light, wheeling turnover, minimized bouncing, and greater quadriceps flexibility and knee flexion can help you achieve the right stride length and cadence for improved speeds at reduced injury risk, whether you're on an easy recovery run or in the midst of an intense track workout.
References:
Run Strong ed. by Kevin Beck, Human Kinetics, Champaign, IL, 2005
Improving Stride Mechanics by Jack Youngren, pp. 12-20
Creating Leg Turnover and Raw Speed by Greg McMillan, pp. 26-27
Daniels' Running Formula by Jack Daniels, Ph.D., Human Kinetics, Champaign, IL, 1998, pp. 80-82