Running Cadence Part I
Running Cadence
What is cadence and what does it mean for running?
If you know what cadence is, you can skip this paragraph. For the rest of you, Merriam Webster lists two definitions of cadence that are fitting for our purposes: (1) the beat, time, or measure of rhythmical motion or activity; (2) a regular and repeated pattern of activity. In music we can think of cadence as the number of beats per minute and we can apply this concept to running in exactly the same way. So, let’s simplify our definition to mean the number of steps, or the number of times our feet beat the ground, per minute. If you are running a certain pace, let's say seven minutes per mile and you increase the number of steps you take each minute, you have increased your cadence. You’ve increased the beat. The hardest part of this to wrap your head around is that you can be running different speeds and have the same cadence. For example, I can run very slowly and take quick steps (increase turnover) and have the same cadence as when I am running quickly. I accomplish this by shortening my stride and taking more steps. I can also do the opposite and take longer strides while running quickly and have the same cadence as when I run slowly.
Why may running cadence be important?
Cadence is one important gait component researchers are looking at because small changes in cadence can have a big impact on running mechanics. On top of that, many gait characteristics that have been associated with a slower cadence have been identified as factors that can contribute to running related injuries. Let’s talk about why that is and discuss some of these non-ideal gait mechanics. Changes in cadence result in a change in stride length. Generally a lower cadence means a longer stride length and a higher cadence means a shorter stride length. Here’s what happens with an increased cadence and a decrease in stride length: (1) decreased braking force, (2) decreased peak vertical ground reaction force, (3) decreased peak hip adduction angle, (4) decreased peak knee flexion angles, (5) an increase in knee flexion angle at initial contact, (6) decreased vertical displacement and stride length, (7) decreased heel strike distance and ankle dorsiflexion at initial contact.1 Did you follow and understand all those components? That’s a lot to digest and I’d be surprised if they all make sense so we’ll take a look at each one individually.
Decreased braking force
As we talked about in an earlier post and in accordance with Newton’s laws, every action has an equal and opposite reaction. This means, when your foot strikes the ground, the ground strikes your foot back with the same amount of force and in the opposite direction. If you’re running with a long stride (decreased cadence) your foot will strike the ground further in front of you and your leg will be in a more horizontal position. Conversely, if you’re running with a shorter stride, your foot will strike the ground closer to your body and your leg will be in a more vertical position. So, when you strike the ground with your foot way out in front of you and in a more horizontal position, the ground pushes back toward your body in a more horizontal position (see the pictures below). This is what we refer to as braking force because the ground is pushing back toward you and slowing your forward movement. Now, when you’re running with an increased cadence and your foot strikes the ground just in front of or directly under your body, the ground pushes directly upward into your body. Not only does this not slow your body down as much, or put as much force through your leg, but it allows the spring which is made up of the muscles and tendons of your leg to absorb the force and release it during the push off phase of gait. This isn’t just a way to decrease injury, but it’s a great way to boost performance!
Heel strike with slow cadence
Notice how the angle of the force is directed backward towards the body increasing the braking force and decreasing efficiency.
Heel strike with fast cadence
Notice how the angle of the force acting on the ground is more upward and less horizontal which decreases the braking force on the body.
Decreased peak vertical ground reaction force
Vertical ground reaction force is related to braking force, but instead of acting on your body in a horizontal direction like braking force does, it exerts force on your body in more of a vertical direction. As we’ve already discussed, when your foot contacts the ground and you load your weight onto your leg, the ground pushes back with the same amount of force. When cadence is increased the amount of force you put through your leg into the ground decreases. This happens for a couple of different reasons, all of which allow the leg to be more springy and less rigid. The first way your body achieves this is by having a knee that partially bent, not straight when you foot hits the ground. This allows your knee to act more like a shock absorber and dissipate force versus rigidly striking the ground. A second reason is that your foot contacts the ground in more of a pronated versus a supinated position. In this position, the joints of the foot unlock and the foot absorbs force versus delivering all the force into the ground and then back up the leg. Lastly, the foot strikes the ground in more of a plantar flexed position which means more of the foot makes contact with the ground, not just the heel. When more of the foot contacts the ground, force is spread out throughout the foot and not just concentrated in one small area.
Decreased peak hip adduction angle
Abduction and adduction are two terms that are used to describe the position of the leg in regards to the hip. In a more adducted position, the leg moves more under the body and toward the midline, in a more abducted position the leg moves away from the midline and more directly under the hip joint. Too much hip adduction angulation can be problematic as it changes how force is transmitted through the knee. As the leg moves more into an adducted position, one side of the knee is compressed and the other side is stretched. If this situation happens for a prolonged period of time, the knee undergoes abnormal wear and tear, which can result in arthritis and damage to the cartilage in the knee. Increasing running cadence can result in decreased knee angulation, proper force transmission through the knee, and less wear and tear on the joint surfaces.
Decreased peak knee flexion angle
When running, as you load your weight onto your leg, the weight of your body and the force it has generated moving forward pushes on your knee and tries to make it bend. While this is happening, your quadriceps muscles, which straighten your knee, are working to keep your knee from bending. They control and slow the bend and then work to straighten your knee as you move toward the push off phase of gait. This means, the more your knee is bent, the harder your quadriceps have to work to control this force, and the more torque or wear and tear is placed on the joint.
As we’ve already discussed, at a slower cadence, the body experiences a higher ground reaction force and higher braking forces. Conversely, at a higher cadence the ground reaction force and braking force will be lower. Since ground reaction and braking forces are lower, your knee does not need to bend as much to control and dissipate these forces. As a result your quadriceps muscles and your knees undergo less wear and tear.
Peak knee flexion angle at slow cadence
Peak knee flexion angle with fast cadence
Increased knee flexion angle at initial contact
If you’re running with a longer stride and a decreased cadence, your leg will strike the ground further out in front of your body. The further your leg is out in front of you when you strike the ground the straighter, or more extended your knee will have to be in order to reach the ground. The closer to your body your leg lands, the more bent your knee will be. This is important because the straighter your leg and knee are, the less able your leg is to absorb and dissipate force. When you have a slight bend in your knee, you are better able to absorb and dampen the force of your leg striking the ground. The better you are able to absorb and dissipate force, the less likely you are to sustain an injury.
Slow cadence knee flexion angle at initial contact
Fast cadence knee flexion angle at initial contact
Decreased vertical displacement and stride length
Decreased vertical displacement means basically means your body doesn’t bounce up and down as much. As your cadence increases, you bounce less, simple as that. If you’ve ever jumped either on a trampoline or on the ground, then you’ll understand, the higher you jump, the harder you will hit the ground which means the harder the ground will hit you back. If you can manage to increase your cadence and decrease your bounce height (vertical displacement), you will hit the ground softer. As we’ve already discussed, decreasing your stride length will decrease braking force and ground reaction force.
Decreased heel strike distance and ankle dorsiflexion at initial contact
Decreased heel strike distance essentially means you strike the ground closer to your body. As we’ve already discussed, the closer your foot is to your body when you strike the ground, the lower the ground reaction and braking forces will be. When your foot strikes the ground further out in front of your body not only are forces higher just because of this, but they are higher because your ankle is in a more dorsiflexed (bent up position). This results in more force transmission through the leg for multiple reasons. (1) When the ankle is in a more dorsiflexed position, the foot is generally in a more supinated or stable and rigid position. This means the foot is not able to dissipate force as well and force is sent up the leg. (2) When the foot is in a dorsiflexed position, you are more likely to land on your heel. When you strike the ground with just the heel, force is not spread out through the entire foot and is more likely to get sent up through the leg.
To compound problems, when you land on your heel the muscles on the front of your leg have to work hard in order to slowly lower your foot to the ground. If the muscles on the front of your leg don’t control lowering, your foot will slap the ground and this will cause other problems. Over time, if the muscles on the front of your leg are having to work hard to control your foot as it lowers to the ground, they can become over worked and you can develop shin splints, compartment syndrome, and other issues. So, this is yet another reason you want to make sure your foot lands closer to your body when you strike the ground.
In the interest of keeping this post a reasonable length, I’ve decided to break it into two parts. In this first part, we discussed all the ways increasing cadence can improve gait mechanics. We also discussed how all of these changes can play a role in injury prevention and in boosting running performance. I encourage you to take the time to read and re-read this post so you fully understand everything that was discussed. When you are able to understand all of these concepts and put them to work for you, they can be very effective in preventing injury and improving your performance. Now, with that being said, don’t go and change your cadence a whole lot until we get to the second part of this post. In that post we will discuss the potential downsides of increasing cadence, what an ideal cadence is in steps per minute, how much of a change is appropriate for you, and how long it takes to make a lasting change in your cadence. I hope you enjoyed this post. Stay tuned and I’ll catch you in part II
