Biomechanical Efficiency in Distance Running by Dominique Stasulli

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[This is a guest post by Dominique Stasulli. Dominique participated in the internship program at Athletic Lab]

Have you checked your form lately? Do you know the proper stride mechanics that’ll make you the most efficient runner possible? Running economy is defined as the energy utilized under a submaximal velocity, usually measured by the consumption of oxygen, per kilometer run, per kilogram body weight. The greater the running economy, the more efficient the runner, the better the performance. There are numerous factors both genetic and adaptive that can affect an athlete’s efficiency, with the focus here being the individual’s biomechanics. Let’s take a look at what goes into efficient form and break down each phase into its biomechanical constituents. The common errors that occur in each phase will also be addressed to give the reader an idea of what to look for in an athlete’s form. After reading, one should have a better understanding of what it takes to improve his or her running economy to minimize energy expenditure over long distances.

Stride mechanics can be broken down into the following foci in endurance running: foot placement, toe-off, thrust, rotation, and torsion. Constant low-speed running should be visualized as a cyclic wheel motion, rolling and circular without any jerky or shock-generating movements. The mechanics for high-speed running and endurance running are nearly equal, however, the displacement of energy is where the two differ. Reactivity and avoiding wasteful rotation should be emphasized in both. Bosch and Klomp wrote in Running: Biomechanics and Exercise Physiology Applied in Practice, that the amount of energy needed to oscillate the legs can be decreased by limiting the degree of movement of the entire pendular action; this can be achieved by keeping the support phase short (when one foot is in contact with the ground), and by pushing off “reactively” (1). Reactive muscles essentially recycle energy between phases as a function of muscle elasticity, and ultimately save the athlete energy costs over the long haul. Long ground-contact results in a greater energy expenditure and less recycling. Rotation, especially when dealing with the shoulders, trunk and pelvis, requires the body to use unnecessary energy to both produce the rotation and subsequently compensate for its inefficiency (1). Both errors will be examined in greater detail momentarily.

The most efficient runners exemplify a footstrike in which the foot lands directly under the hip at the moment when the entire weight of the body comes to rest on the support leg. Backward flexion of the hip is key in bringing that foot around as quickly as possible, and virtually eliminates heel-striking as a result. Without much backward flexion of the hip, the foot will land in front of the body’s center of gravity with the heel striking first, far in front of the hip, causing a deceleration effect (1). This braking effect is metabolically expensive and wasteful.

The general posture of the trunk should be more or less upright to avoid over- or underworking the hamstrings and the displacement of stored energy (1). The carrying angle of the arms is typically quite small and high to avoid fatiguing the muscles around the shoulder girdle (1). The motion of the arms is not linear or rigid as in sprinting, but more fluid along the front of the body, naturally flowing with the torsion of the trunk and pelvis along the longitudinal axis (1). Torsion of the trunk should not be confused with rotation. In rotation, the shoulder compensates for hip rotation by moving in the opposite direction, backwards as the same leg pushes off (1). Torsion, the correct motion, has the shoulder pushing forward on the same side that the leg toes-off (1); the shoulders seemingly “open up” to the driving knee, perfectly balancing the torsion, effectively cancelling out the rotation of shoulders and pelvis.

At the moment of toe-off in the support leg, the knee angle should be significantly less than 180 degrees; this ensures that the drive or thrust is angled backwards with the heel flip and the workload is directed onto the hamstrings (1). The hamstrings are the key players driving the stride; the stronger the pull of the hamstrings, the less vertical displacement of the runner, and thus the greater the focus on horizontal propulsion. Vertical motion is yet another energy leech and should be kept to a minimum. Less economical runners exhibit greater vertical impulses (2). A certain degree is necessary to give the hamstrings enough room to work through full oscillation, but this can be achieved by strengthening the small gluteal and dorsal muscles of the lower back (1). If these muscles are weak then the rectus femoris (central quadriceps muscle) needs to drive the vertical push-off, making for a costly compensation (1).

Sitting the hips low is a common adaptation of distance runners, simply because the rhythm of movement is slower than fast-paced running. This is okay, as long as inertia is not allowed to enter between the energy storing and unloading phases, since any loss in tension of the lower limb muscles and tendons will result in an enormous loss in energy (1, 3). This sloppy, loose technique is typically seen in runners with low power and reactivity or faulty coordination. Resistance training and explosive plyometrics are two proven strategies for improving lower-body stiffness to enhance running performance (3). Another point worth mentioning is that lack of tension around the ankle, lethargic dorsiflexion, causes ground contact time to increase, expending stored energy from the Achilles and surrounding tendons (1). On the contrary, too much plantar flexion of the ankle does not allow the muscles to tighten sufficiently enough for a reactive ground contact. The ankle should be stiff and only slightly dorsiflexed at ground contact.

The propulsive phase is where force is applied to the ground through the lower limbs in order to obtain forward horizontal displacement (2). Any deviation in weight or force distribution can be detrimental to the athlete’s running economy, since this subphase of ground contact is the most metabolically demanding of the entire gait cycle (2). The error most commonly seen here is the athlete who only runs with his or her legs, lacking tension in the abdominal and gluteal muscles, and not allowing the trunk to participate in propulsion. The act of propulsion, or thrust, should be carried out earlier in the support phase rather than later, to avoid long-axis rotation of the trunk (1).

During the floating phase, when both feet are off the ground, some common errors should be noted. A lack of sufficient knee drive results in lax plantar flexion of the ankle in the trail leg. This can be noted in an athlete who’s trailing knee lags behind the stance leg at the point of maximum ground contact. The swing leg’s knee should be already quite forward at this point in the stride (1). A recent 2014 study by Santos-Concejero and colleagues, investigated stride angle as a predictor of running economy (2). Stride angle is the tangent between the athlete’s vertical and horizontal displacement after toe-off to touchdown. Too great of an angle indicates vertical waste, and too low of an angle hinders stride length, possibly the most influential factor in running economy (2). Stride angle serves as a marker for the runner’s ability to maximize swing time and effectively transfer energy during quick ground contact (2), making it a solid assessment point for any coach.

Keeping these points in mind regarding each phase of gait analysis, coaches and athletes alike can gain better insight as to where precious metabolic energy is being lost in form. Stride mechanics are the most direct player in running economy and efficiency, but luckily also the most trainable. In practice, it is wise to focus on no more than one correction to technique at a time, giving enough time for neuromuscular adaptation to occur and become subconsciously integrated into the athlete’s natural stride mechanics. This adaptation occurs relatively quickly, as a function of age, with young children and adolescents being extremely neuro-adaptive. Once a completely efficient stride is in place and mechanically second-nature, the improvements in performance will soon follow, since the entire metabolic demand on form is reduced to a bare minimum and the focus shifts to cardio-circulatory economy rather than biomechanical.

REFERENCES

  • Bosch, F. & Klomp, R. Running: biomechanics and exercise physiology applied in practice. Maarssen, Netherlands: Elsevier (2005). Chapter 3.4: pgs 181-88. Print.
  • Santos-Concejero, J, Tam, N, Granados, C, Irazusta, J, Bidaurrazaga-Letona, I, Zavala-Lili, J, & Gil, SM. “Stride angle as a novel indicator of running economy in well-trained runners.” Journal of Strength and Conditioning Research 28:7 (July 2014). Pgs 1889-95.
  • Barnes, KR, McGuigan, MR, & Kilding, AE. “Lower-body determinants of running economy in male and female distance runners.” Journal of Strength and Conditioning Research 28:5 (May 2014). Pgs 1289-95.
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