[This is a guest blog by Erin Ritterbusch who is currently an intern at Athletic Lab. Erin is a recent graduate of Auburn University where she received her Master’s degree in Exercise Science with a concentration in biomechanics.]

Growing up, my dad, an orthopedic surgeon, always told me to be wary of the treadmill. I really never understood those implications until I delved into the biomechanics of running during my master’s program. Surprisingly, I was not able to find a lot of research articles on this topic. Anyone who has run outside as well as on a treadmill can attest to the fact that these are two very different feelings. However, does this mean that we are more susceptible to injury? I believe it does because we have to alter the way that we run in order to compensate for what is propelling this motion. When we run on flat ground, we are using our own momentum to push us forward to accelerate, to maintain, or to slow down. However, on a treadmill, the belt below us is pulling us backwards with every step we take.

An article I came across on triathlete.com written by “The Gait Guys”, as they are known, made some very strong points about how exactly the treadmill affects your stride and muscles. To make a comparison, running on the treadmill is similar to running downhill. The backward motion of the belt catches the heel and pulls the forefoot onto the belt when your lead foot comes into contact with the treadmill belt. This accelerated motion demands a higher level of muscle strength in the anterior part of your shins. This is what causes such a prevalence of shin splints in those who run frequently on treadmills. There is also a neurologic “stretch reflex” present to protect muscles from tearing by strengthening the contraction and sends a signal to the antagonist muscles to relax. This stretch reflex that occurs in the hip flexors inhibits the hip extensors (glutes) from firing. The gluteal muscles are what normally work to draw the leg backwards when running and the motion of the treadmill can inhibit that function. If your lumbopelvic hip complex (see my previous blog to learn more about the LPHC) isn’t being engaged properly or adequately enough, the over activity of the hip flexors will then draw the pelvis forward which increases the arch in your spine, which can lead to back pain.

This stretch reflex can also inhibit the quads because of the stretching of the hamstrings as the knee is extended more from the treadmill than in road running. The moving belt also has a tendency to allow for more ankle dorsiflexion, which promotes more heel striking. Heel striking when running increases risks to injury because it occurs in front of your center of gravity and a larger downward motion after impact. This causes a “deceleration” or slowing down at impact between the heel and the ground, leading to biomechanical faults such as Achilles injuries or calf shortness. “Changes in joint kinematics at heel strike, such as knee- and ankle-flexion angles, would accompany any change in stride length and cadence…” (Gerlach, 661). Overall, these changes can affect a person’s gait and different muscles up the kinetic chain and these altered joint arthrokinematics increase stresses up the chain, which can lead to injury.

The other point to make is the consistency of the treadmill versus human variability of road running. With road running, you are able to dictate your speed, which allows you to control how long you are spending in each phase of gait. The other side of looking at this is that you don’t have a lot time to compensate because of the constant velocity of the belt, which can more or less cause more problems up the chain if you allow for them. Also, there isn’t much, if any, give to the surface of the treadmill, while in road running most surfaces have some give to them. Without any cushion as you land with each stride, this can be hard on your joints, such as your knees, especially for women who are shown to be more susceptible to knee injury. Overuse injury is more likely to occur if you consistently run on a treadmill as well. Flat ground possesses varied surfaces with each foot contact while the treadmill gives you the same surface over and over again. This unchanging surface promotes a repetitive stress of the same muscles and can result in injury. Not to mention, it isn’t hard to fall off the treadmill and hurt yourself if you aren’t paying enough attention. Trust me, I would know.

However, due to climate constraints or location, the treadmill may be the only option. The Gait Guys suggest that you should find a speed and incline that allows you to feel like you are slightly pushing the belt backwards instead of the belt pulling you backward with each stride. Being aware of gait differences and being in tune to how it feels may be sufficient enough in reducing injury on the treadmill.

References:

http://www.triathlete.com/2012/02/training/the-truth-about-treadmills_48165

Gerlach, Kristen E., et al. “Kinetic changes with fatigue and relationship to injury in female runners.” Medicine and science in sports and exercise 37.4 (2005): 657-663.