Sports Watches – Cadence & Vertical Oscillation

You’ve completed your run and are going through your saved training run, and noticed that you have a few more measurements under running dynamics: cadence and vertical oscillation. (Not all devices record these measurements, and some of these measurements, such as vertical oscillation, are only possible if wearing a HR belt, and not wrist-based HR). Great! So what now? What do they mean? Am I running weirdly? Are these values normal? Hopefully I can help answer a few of these questions….

 

Running economy (RE) refers to the aerobic demand (oxygen consumption) of running at a given submaximal speed. Typically runners with good RE not only use less oxygen (are more efficient in using oxygen), but also tend to use less energy than runners with poor RE. Step rate (cadence) and vertical oscillation are two measurements which can be used to enhance/improve your RE.

 

Step rate, namely the number of steps you take per minute has been studied to improve RE as well as lower the risk of injury (1). It has been indicated that small increases in the step rate from your preferred/normal step rate, reduces forces at the ankle, knee and hip, and thus may reduce the risk of injury.

In addition to the step rate, one needs to consider the stride length. Stride length is taken from the one heel strike of the right foot to the next heel strike of the same foot (visa versa for the left, see image below). At a constant speed, stride length and step rate have an inverse relationship: if step rate increases, stride shortens, while if step rate decreases, stride increases.

stride-length-1

 

So what is the optimal cadence? What values should I be aiming for?

The typical cadence in most long distance runners is between 150 and 200 steps per minute with the optimal being recorded at 180 steps per minute – this is for optimal running efficiency.

So how do I make sure I am making 180 steps per minute? There are two ways:

  1. Get a sound track at 180 beats per minute, OR…
  2.  Use the metronome function on your watch, set it at 180 steps per minute and sorted.

Ok, you’ve now got the cadence down to the optimal number of steps per minute, but what about the looming vertical oscillation that keeps popping up after a run – what’s that all about?

Have you ever watched professional runners run, and noticed how their upper bodies don’t move much, but their legs are going crazy? Similar to what you would be seeing on a flight with the air hostess, especially in a slightly turbulent flight. All of this is related to vertical oscillation.

 

Vertical Oscillation is the degree of so-called “bounce” in your running motion. The typical vertical oscillation has been recorded between 6 to 13cm with elite runners falling in the lower end of this range. This one measurement has been shown to correlate with running efficiency, and not wasting energy as you rack up the km. How? Reduce the amount of “bounce” by increasing your cadence.

So what is so bad about this bounce? It’s got to do with the movement of your centre of mass (centre of gravity; COG) (2). An increase in the vertical oscillation is as a result of the increased displacement of the COG, which results in an increase in the amount of energy required to keep you balance (you’ve now increased the workload of the central nervous system). Now don’t think that you won’t get a movement in your COG – there will always be a displacement of the COG when moving, as the body adjusts to keep you balanced. As the images below show: your centre of gravity (COG)/centre of mass will move as one moves through the different phases of running – heel strike, mid-stance, toe-off.

centre-of-mass-changesnatural-running

Successful endurance runners have been characterized by less vertical oscillation, longer strides, and less change in velocity during the ground contact (3).

 

Biomechanically speaking, there are many different “angles” that one takes in further understanding how well one runs, and combining this with physiology, gives further insight into the kinematics of your running style, and helps provide corrective suggestions to enhance overall performance as well as preventing risk of injury. Look out for places that do biomechanical analyses of running – they could help you understand your running a little better – if you’re taking it a little more seriously.

 

 

References:

  1. Richardson, J.L. (2013). Effect of step rate on foot strike pattern and running economy in novice runners. All Graduate Plan B and other Reports. Paper 287.
  2. Winter, D.A. (1995). Human balance and posture control during standing and walking. Gait and Posture, 3(4).
  3. Kyröläinene, H., Belli, A. and Komi, P.V. (2001). Biomechanical factors affecting running economy. Med. Sci. Sports Exerc. 33(8): 1330-1337.
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