Is Drag Important for Runners?
Cyclists are notorious for attempting to reduce the effects of drag as much as possible. Aerodynamic helmets, shaved legs, and aero bars are the norm within this sport. Runners, on the other hand, seemingly don’t care about the effects of drag on their performance, which begs the question: Is drag important for runners? Here, drag, as well as factors that affect drag and how to overcome them, will be discussed.
What is Drag?
Simply put, there are a number of forces acting against a runner as his or her body is propelled forward. The three most important factors are propulsion, wind, and drag. Propulsion is the force applied by the runner’s muscles to achieve forward, accelerating motion. Wind, which can be helpful or detrimental, causes further acceleration if the wind is at the runner’s back.
Alternatively, deceleration occurs if the wind is opposing the runner. Drag is the force of air resistance that is applied by the wind, causing further deceleration. Even on calm days, drag can play a role in a runner’s ultimate deceleration, particularly as a runner’s speed increases.
Factors that Affect Drag
There are a number of factors that affect the amount of drag a runner experiences, including:
In cycling, the difference between a casually fitting jersey and a form-fitting jersey is 91 seconds over the course of a 40k time trial. How do those baggy running shorts flapping in the wind or that loose t-shirt compare for runners? According to one study1, the contribution of a runner’s clothing to drag can be significant. Here, the study’s authors looked at the effects of drag on both sprinters and distance runners while using a wind tunnel. By reducing the amount of clothing a runner was wearing, he or she could decrease wind resistance by approximately 2%, which had large implications for performance, particularly at the elite level.
Another aspect that can affect a runner’s aerodynamics is hair. For women, even the difference between a braid and a ponytail can change the runner’s drag force. In the same 40k time trial described above, women who put their hair in a braid were able to shave 14 seconds from their overall time. For runners, hair may play an even more pivotal role, as there are no aerodynamic helmets to block the majority of the wind. Runners can decrease the effects of drag by keeping their hair short and close to their head.
Body and Facial Hair
For men, body and facial hair are another factor that increases wind resistance. Cyclists who shaved their legs reduced their time trial time by 70 seconds, which is significant over the course of 40k. For runners, having a smooth body might not produce the same impressive results (no such studies have been performed); however, there is no evidence to suggest that body hair (particularly long beards) wouldn’t slow down finishing times to an extent.
Runners are well aware that poor running form reduces a runner’s efficiency; however, how much of a factor is aerodynamic drag in this equation? In short, excessive movement2 of limbs produces additional wind resistance, which can ultimately cause deceleration. For instance, runners should move their arms strictly in a forward and backward motion.
When elbows move from side to side, instead of back and forth, they create additional wind resistance that ultimately affects a runner’s forward momentum. The above study looked at the aerodynamic cost of leg position. In speed running, maximum speed is limited by the athlete’s ability to rotate his or her legs forward and backward, relative the hip joint. If a runner has any inversion within his or her hips that causes ankles to deviate from the plane of strict back and forth motion, wind resistance will be increased. Therefore, poor biomechanics in the lower legs, particularly due to poor hip strength, hinders a runner’s aerodynamics.
Poor Race Strategy
Additionally, the way in which a runner approaches his or her race strategy3 can affect the amount of wind resistance experienced, especially among sprinters. In general, sprinters rely on fast acceleration at the start of their race and the ability to maintain a high velocity.
However, runners can only maintain all-out effort for a limited period of time before their running form diminishes, which results in greater drag and deceleration. Scientists found that for sprints lasting less than 80 – 100 seconds, it is energetically favorable to approach the race as an all-out effort despite the aerodynamic cost at the end; while for longer races an even pacing strategy is energetically ideal.
Just as clothing and hair can affect a runner’s air resistance, so can the seemingly smallest of gimmicky items. Tutu’s, jewelry, hair ribbons, and ”schwings” all slow down a runner and increase the energetic costs of his or her movement. Even shoe laces that are too big increase a runner’s overall drag.
Thus far, everything mentioned that affects the amount of drag experienced by a runner is largely based on controllable factors. However, one aspect that a runner cannot control is his or her height. Height increases body mass disproportionately, which means that a taller runner will experience more air resistance on a relative scale than a shorter runner.
The amount of power that must be produced in order to overcome the effects of drag as a runner’s height increases is very high. Until Usain Bolt’s world record performance, the average height of world-class sprinters was 5’11, whereas Bolt is 6’5’’. Among marathoners, the list of distance runners who are over 6’ tall is a short one.
How Does Drag Affect Runners?
First, it should be noted that drag does not affect all runners equally; at least, not runners of all paces. In cycling, drag effects are first noted at 15 km/hour, which is equivalent to 4:00/km, or 6:24 per mile pace, for runners. Therefore, on a calm day the typical runner does not need to worry about the energy losses due to drag.
However, for athletes who are trying to make marginal gains, even a 1 – 2% reduction in drag can have performance enhancing implications. For instance, one study1 suggests that 2% drag reduction equates to a time savings of 0.01 seconds in the 100 m dash, and 5.6 seconds in the marathon. At the elite level, even a tiny fraction of time is important.
In another study4, runners were placed in a wind tunnel and the effects of drag were compared to downhill and uphill treadmill running. When the wind velocity was greater than 15 meters per second (approximately 33 miles per hour), runners leaned into the wind which converted drag into body lift and caused further deceleration.
However, even on calm days with low wind, the energetic cost of overcoming drag for sprinters is 7.8% when running at a speed faster than 22 miles per hour; 4% for middle distance runners when running faster than 13 miles per hour; and 2% for long distance runners covering ground faster than 11 miles per hour. While the average runner does not compete at these speeds, when the opposite is true (i.e. an athlete is running into an 11 mile per hour wind), overcoming drag forces requires a significant amount of energy.
In another important study5, physiological factors were determined as a result of drag. For instance, it was found that oxygen intake increases as a square of wind velocity, meaning that runners work disproportionately harder as the wind grows stronger. Using a real example, for a 65 kg runner at marathon effort, oxygen intake significantly increased from 3 liters per minute with minimal wind, to 5 liters per minute at a wind velocity of 40 miles per hour.
Since running at marathon pace (here, approximately 6:00 per mile) only requires 2% of a runner’s energy in order to overcome drag on a calm day, it is easy to see that as the wind velocity increases, marathoners (and by corollary mid distance runners and sprinters) must produce a significant amount of power in order to overcome air resistance as evidenced by the changes in oxygen intake.
How to Overcome Drag
Regardless of whether you are an elite runner or a back-of-the-packer aiming for a personal best on a windy day, there are a number of strategies available for overcoming wind resistance.
Perhaps one of the most energetically favorable steps that a runner can take on race day is to draft behind another athlete or group of runners. For instance, in the seminal study5 on running and drag forces, it was found that air resistance in track running accounts for 7.5% of the total energy cost at middle distance speed and 13% at sprint speed.
Middle distance athletes who ran 1 m behind another runner virtually eliminated air resistance and reduced their oxygen intake by 6.5%. In fact, a large component of the sub-2 hour marathon project relies on the concept of drafting. Exercise physiologists believe that if these marathoners are able to draft off a person or vehicle for the entire duration of 26.2 miles, as opposed to the halfway point, as occurs in most major marathons, a time drop of 2 – 3 minutes from the current marathon world record (2:02:57) is possible. This time drop does not factor other performance enhancements into the equation.
While drafting is great for runners who are near other athletes (or who are part of an elaborate optimization experiment, as is the case for the sub-2-hour marathon project), what can runners who are winning their race or are relegated to lanes do to overcome drag? If you watched the 2016 Rio Olympics, you might have noticed Aeroswift Tape on Nike’s top athletes. According to Nike, this tape (which resembles kinesio tape but has a specialized exterior) reduced air resistance by 2 – 3% in wind tunnel tests.
Finally, an important consideration for reducing the effects of drag is simply optimizing your race day outfit. Form fitting clothes, cropped or braided hair, shaved legs, and the removal of additional accessories such as necklaces, earrings, and non-necessary gear can help runners make marginal improvements which might be the difference between a great performance and a personal best.
1. Kyle, C. R., & Caiozzo, V. J. (1986). The effect of athletic clothing aerodynamics upon running speed. Medicine & Science in Sports & Exercise, 18(5). doi:10.1249/00005768-198610000-00003 Link
2. Schenau, G. J., Koning, J. J., & Groot, G. D. (1994). Optimisation of Sprinting Performance in Running, Cycling and Speed Skating. Sports Medicine, 17(4), 259-275. doi:10.2165/00007256-199417040-00006 Link
3. Hanley, B. (2014). Pacing profiles and pack running at the IAAF World Half Marathon Championships. Journal of Sports Sciences, 33(11), 1189-1195. doi:10.1080/02640414.2014.988742 Link
4. Davies CTM. Effects of wind assistance and resistance on the forward motion of a runner. J Appl Physiol 48: 702–709, 1980 Link
5. Pugh, L. G. (1971). The influence of wind resistance in running and walking and the mechanical efficiency of work against horizontal or vertical forces. The Journal of Physiology, 213(2), 255-276. doi:10.1113/jphysiol.1971.sp009381 Link