Running Science

by Owen Anderson

  The problems associated with a large positive shin angle can be discerned from table 5.1, which examines shin angle in the momentous 2011 Boston Marathon. (In this particular race, two men completed the competition in times faster than the world record, and American runner Desiree Davila made a strong bid to win the race outright.)

  The reader will note that the first-, second-, and third-place male finishers all come from the group with smaller positive shin angles while Ryan Hall, the American entrant, had a large shin angle and finished fourth. On the women’s side, the winner, Caroline Kilel, ran with a relatively small shin angle, 65 percent smaller than that of Davila, the second-place American finisher. It is tempting to speculate that Davila could have beaten Kilel had she not had to overcome greater braking forces with each step. It is also reasonable to assume that Hall would have been much closer to Geoffrey Mutai and Moses Mosop had he employed a smaller shin angle.

  Stride Rate

  Having a relatively high stride rate is an element of form associated with higher performance and enhanced economy. Studies reveal that elite runners almost always use stride rates of 180 steps per minute or greater during competitive situations, while less accomplished runners often move along at about 170 steps per minute. It is interesting to note that increasing stride rate—not elongating stride length—is also the primary way in which most runners upgrade their maximal running velocity. Runners can work on increasing stride rate by running with a watch or metronome that beeps at the appropriate rate (3 times per second or 90 times per minute if one foot is being monitored). Alternatively, contacts with the right or left foot can be counted over a 1-minute period, and stride rate can consciously be adjusted upward if it is found to be slow. Using a midfoot strike and conducting explosive training also tend to heighten stride rate.

  Pose Method

  A so-called revolutionary new way of running was introduced by running-form researcher Nicholas Romanov. Called the pose running method, the technique involves striking the ground with the midfoot and maintaining a flexed knee during the stance phase of the gait cycle. The characteristic pose geometry is achieved with a simultaneous vertical alignment of the ipsilateral shoulder, hip, and heel of the supporting foot (see figure 5.5). From this posture, a runner is supposed to lean forward; in fact, movement is initiated with the forward fall of the upper body. As motion of the upper body is initiated, the supporting foot is lifted by flexing the knee; actual pushing away from the supporting surface (i.e., the ground) is avoided. Note how different this is from usual running. In each successive stance, contact is made with the ground by the midfoot (i.e., the ball of the foot), not the toes or the heel, and flexed knees are maintained throughout the entire gait cycle.

  Figure 5.5 Vertical alignment of the ipsilateral shoulder, hip, and heel of the supporting foot as prescribed by the pose method.

  The pose method seems to be an attempt to let gravity provide a significant fraction of the energy required to move forward. Essentially, one is falling forward and then catching oneself with the forward-swinging foot instead of producing high-energy-cost, propulsive forces against the ground with the various leg muscles. There is an intuitive appeal to this approach: A similar pattern of gait has been observed in scientific studies of Kenyan women who manage to carry increasingly heavy loads without significantly expanding their energy expenditure.16

  In research carried out by Romanov and Tim Noakes of the University of Cape Town, the biomechanics of pose running were compared with heel-toe running and the midfoot-landing style.17 Twenty male and female runners who normally ran with a heel-toe style were recruited from running clubs in the Cape Town area and were given instructions on how to run using the midfoot style and also using the pose method. It took them about 15 minutes to learn how to run with the midfoot-landing style and 7.5 hours to assimilate the pose technique. All of the runners then ran 10 different trials at self-selected speeds with each of the three styles of running (heel-toe, midfoot, and pose), and data related to running speed and biomechanical factors were collected as they ran.

  As it turned out, the average speed selected by the subjects for midfoot running was about 6 percent faster than that used for pose running. Pose running was associated with shorter stride lengths and smaller vertical oscillations of the pelvic girdle compared with both heel-toe and midfoot running. With pose, the feet are kept closer to the ground and stride lengths are shorter, making a smaller arc of the center of mass as the body moves forward from one foot to the other. Naturally, since the pose method involves falling forward rather than launching oneself upward and forward with a strong push on the ground, stride lengths and vertical oscillations tend to be diminished.

  Horizontal propulsive forces were lower with the pose method than with midfoot and heel-toe running. Although peak knee flexion during the swing phase of the gait cycle was the same in all three running styles, the knee flexed to a greater extent in preparation for initial foot contact with pose than with the other two styles. Finally, the eccentric work done at the knee during stance was less with pose than with heel-toe and midfoot running. Since the pose knee is already highly flexed when the foot hits the ground, the quads have very little eccentric work to do to control knee flexion during the stance phase. With both midfoot and heel-toe running, the knee is straighter when the foot strikes pay dirt, so the quads have a much bigger job controlling the resulting knee flexion that occurs, and thus eccentric work is greater. (The quads stretch as they work while the foot is on the ground, and so their task is termed eccentric.)

  This might suggest that pose running would be more economical than the other styles since those large muscles, the quads, are doing less work, but the eccentric work carried out at the ankle during stance was actually greater with pose than with heel-toe and midfoot running. Perplexingly, the researchers did not publish any data related to running economy in relationship to the three styles, nor did they make any attempt to determine the effects of pose running on performance.

  The lower eccentric work carried out at the knee during pose running might suggest that pose is kinder to the knees—or at least to the quads—during running and thus might be recommended for runners with knee problems. However, GRFs were equivalent between pose and midfoot running, even though midfoot running was carried out at a faster pace because GRFs usually increase as running speed goes up. No scientific research has explored the relationship between pose running and injury rates. Anecdotal reports indicate that most of the pose trainees in the study previously described became injured during the two-week period after the adoption of the technique. However, this sharp rise in injury rate might have resulted from the quick transition to pose running and the changes in work output required for various muscles in the pose-trained legs—particularly the muscles around the ankle areas, which have to work harder—rather than a fundamental deficiency in pose running per se. The lesson to be learned is probably not that pose produces many injuries but rather that any shift in running form must be adopted gradually, giving muscles, connective tissues, and nerves a chance to adapt.

  A supporting, follow-up investigation completed by a team of researchers from the Exercise Science Department at Colorado State University at Pueblo revealed that 12 weeks of instruction in the pose method for a group of experienced triathletes actually led to a significant deterioration in running economy along with a reduction in stride length.18 In these pose-trained athletes, the oxygen cost of running at a specific speed actually increased by about 8 percent over the course of the study.

  Conclusion

  The results of scientific research suggest that good running form is linked with the following:

  greater hip extension during the drive phase of gait,

  enhanced knee flexion during swing,

  augmented plantar flexion and a straighter leg during toe-off,

  smaller arm movements,

  limited upper-body motions,

  higher stride rates,

  midfoot str
iking,

  slight forward inclination of the body from the ankles during stance,

  flexion of the leg at the knee at initial moment of foot strike, with the foot relatively close to being under the center of mass (leg is not straight), and

  shin angle at 0 degrees or just slightly positive.

  Coaches and runners can use this information in a very practical way. For example, a runner’s metronome, sold online and at running-specialty stores, can be used to adjust stride rate. The use of a metronome can often help straighten out other form problems in addition to a slow stepping rate: When an athlete who has been running at 170 steps per minute suddenly begins to keep pace with a metronome set at 180, the stride rate obviously improves, the leg tends to be less straight at impact with the ground, the knee is more flexed at impact, the ground-contact pattern is more likely to be midfoot striking, and the foot will be more nearly under center of mass at impact, thus improving the previously described shin angle. Running unshod or with minimal shoes will also help a runner adjust form properly: Barefoot running makes it difficult to be a heel striker and thus increases stride rate and discourages landings where the leg is straight out in front of the body.

  Drills can be used to improve body-forward inclination: The best one is to stand in a running-ready position, lean forward slightly from the ankles, and then run quickly while preserving the forward lean. Runners can consciously work on using smaller arm movements, and upgraded core strength should keep the torso under control. Explosive training should improve hip extension and increase control of the knee during stance.

  Video analysis is critical for monitoring all form adjustments. Before-and-after video examination of foot-strike pattern, stride rate, body inclination, foot position at landing relative to center of mass, knee flexion at landing, arm movement, upper-body stability, and leg dynamics is critical for determining the extent of progress which is being made. Fortunately, great video cameras are now available for less than $100, and the modern cell phone with video capability can also be used to monitor form progressions.

  Chapter 6

  Running Surfaces, Shoes, and Orthotics

  During running, a force greater than two times body weight passes up the leg each time the foot hits the ground.1 Over time, these repetitive impact forces can produce injuries in the muscles, bones, cartilage, tendons, and ligaments of the legs.2

  Runners have two general ways to limit the potentially destructive effects of these impact stresses. First, running shoes contain midsoles that deform, or compress, each time the foot collides with the ground, absorbing and temporarily storing some of the impact force as elastic energy. This absorbed force is prevented from passing upward into the structures of the foot, ankle, shin, calf, knee, thigh, hip, and upper body; instead, it is returned to the running surface to produce some of the propulsive force required for toe-off.

  In addition, a runner’s internal structures (e.g., muscles, tendons, ligaments, bones, joints) compress and change position at impact, muffling the upward transference of force through the leg. With each footfall, the arch of the foot flattens, the ankle joint torques and flexes, the knee undergoes rotation and flexion, and the hip flexes. All these actions soak up impact forces and can reduce direct trauma to muscles, connective tissues, and joints.

  Impact of Running Surfaces

  Many runners believe that the surfaces on which they run also play a role in determining the magnitude of impact forces and thus the risk of injury. Early scientific research seemed to support this idea. In one investigation, subjects who trained on hard concrete floors developed abnormal changes in knee joint cartilage after 2.5 years of training.3 This study helped spawn the notions that running on hard surfaces promotes injury and that endurance running is generally bad for athletes’ knees.

  The so-called athletes in this study were actually sheep, however, and the loading forces and neuromuscular responses to force applications associated with foot-ground impacts are likely to be quite different in humans. No study with human runners has ever detected differences in knee cartilage wear and tear associated with differing running surfaces. In addition, a little-known aspect of the sheep research was that the bones around the sheep’s knees remodeled themselves and were unusually strong after 30 months of walking on concrete.

  Follow-up research with human runners in this area defied conventional wisdom and found that the ground-reaction forces (GRFs) at the foot and the shock transmitted up the leg and through the body after impact with the ground varied little as runners moved from extremely compliant to extremely hard running surfaces.4 As a result, researchers gradually began to believe that runners are subconsciously able to adjust leg stiffness prior to foot strike based on their perceptions of the hardness or stiffness of the surface on which they are running. This view suggests that runners create soft legs that soak up impact forces when they are running on very hard surfaces and stiff legs when they are moving along on yielding terrain. As a result, impact forces passing through the legs are strikingly similar over a wide range of running surface types. Contrary to popular belief, running on concrete is not more damaging to the legs than running on soft sand.

  In one study, researchers at the University of California at Berkeley hypothesized that runners coordinate the actions of the muscles, tendons, and ligaments in their legs so that the lower limbs behave like mechanical springs during ground contact.5 The data obtained in this investigation suggested that the stiffness of a leg spring is highly dependent on the running surface. If this were not true, peak GRF and ground-contact time would change dramatically as athletes ran on different surfaces; in reality, these measures stay relatively constant. The Berkeley researchers found that runners tripled their leg-spring stiffness as they moved across a compliant, soft surface compared with running over hard ground.6 Ground-contact time and center of mass vertical displacement remained constant in spite of a thousand-fold change in running surface stiffness. The inquiry indicated that the sum of leg stiffness and surface stiffness does not change when humans run, even when surface stiffness is altered dramatically. As surface stiffness increases, leg stiffness decreases, and vice-versa.

  Regulation of leg stiffness can occur before runners even take their first steps on a surface of altered resiliency, indicating that a runner’s nervous system creates an expectation of surface hardness before it is actually physically encountered. In a fascinating study, six runners trained at a velocity of 3 meters per second on a track with two types of rubber surface: a compliant, soft surface (surface stiffness = 21.3 kN per meter) and a noncompliant, hard surface (surface stiffness = 533 kN per meter). (A kN is a kiloNewton, or 1,000 Newtons; a Newton is the force required to accelerate a mass of 1 kilogram at a rate of 1 meter per second squared, that is one meter per second per second.) As they ran along the track, the runners completely adjusted leg stiffness for their first steps on the different surface: They decreased leg stiffness by 29 percent between the last step on the soft track and the first step on the hard surface.7 As a result, stride rate and the vertical displacement of the center of mass during stance did not change as the transition was made despite a reduction in running-surface compression (deformation of the running surface in response to being struck by a runner’s foot) from 6 centimeters to less than .25 centimeters per footfall.7

  Sizing Up Running Shoes

  Scientific research on running shoes has often yielded surprising results and has shattered many of the most popular beliefs about running footwear. For example, brand loyalty may be a bad idea from an injury-prevention standpoint, motion-control shoes might actually enhance motion, more expensive shoes could increase the risk of injury, and the life expectancy of running shoes might be much longer than expected.

  Running-shoe midsoles are also surfaces on which endurance runners must run. The research on running surfaces suggests that midsole stiffness would have little effect on the forces transmitted up the leg during ground contact, despite certain manufacturers’
contentions that their running shoes provide better cushioning and thus protection from impact forces than models produced by different companies. Science suggests that runners simply change the stiffness of their legs in response to changes in midsole stiffness, which would mean that all running shoes provide similar levels of cushioning.

  Midsole Stiffness Affects Proprioception

  The story is complicated, however, by the fact that midsoles of modern running shoes also change proprioception, or the way a runner’s foot feels and experiences the running surface. The running-shoe midsole is a kind of mattress on which the foot lands with each foot strike and therefore can be viewed as an information limiter, robbing a runner’s nervous system of key information about the actual running surface. Wearing running shoes may change a runner’s interaction with the ground in the same way that wearing thick gloves alters an individual’s ability to play the piano or determine the texture, density, and stiffness of any object.

  Putting on a pair of running shoes with soft, compressible midsoles might fool a runner’s nervous system and create the illusion that impact forces are slight. This could curb nervous system responsiveness and might prevent a softening, or decrease in stiffness, of the leg itself. It does not seem surprising, then, that scientific evidence suggests that soft, compliant, cushiony midsoles might actually permit the highest impact forces to travel through the legs during running.

  This evidence comes in part from research in which well-trained athletes stepped off a platform 27 inches high and landed either on a compliant mat or on a hard surface. In each case, the impact force transmitted into the leg associated with the hard landing was lower than the force associated with the soft touch-down.8 It appears that athletes make careful musculoskeletal adjustments to minimize shock forces when they know they are going to land on a hard surface and are less careful when they realize that each landing will take place on a soft material. While such findings seem to contradict the research on running surfaces, which indicates that forces are the same across all surfaces, these findings do reinforce the idea that runners automatically adjust leg stiffness in response to the kind of surface on which they are landing.