This week saw the 19th anniversary of parkrun! On Saturday 2nd October 2004, 13 people turned up at Bushy Park in London to complete the very first parkrun. Step forward to last weekend and almost 300,000 individuals completed a parkrun or junior parkrun at almost over 2450 events worldwide, whilst being supported by more than 38,000 volunteers.
Regardless of speed, all runners taking part in a parkrun will be taking a lot of steps during the course of their run. If a runner runs at a cadence of 170 steps per minute (spm) and crosses the line in a time of 30:00 (close to the average finishing time), they will have taken 5100 steps! Which is a lot!
When you go out on your next run, have a go at estimating your cadence by counting the number of steps you do during 60 seconds of running.
Running speed (m/s) = step length (m) * step frequency (spm) / 60
Run time (s) = run distance (m) / running speed (m/s)
Running: Repetition without repetition
Running is seen as an activity requiring a lot of repetitive movement. However, although all steps during a run will move you forwards towards the finishing line, no two steps will ever be exactly the same. Every step will show a subtle difference from every other step. These subtle differences between steps are referred to as movement variability, which has become of increasing interest to researchers during recent years.
To take this to the extreme, I suggest watching the Ministry of Silly Walks. Although very few of us are likely to run like this, what Jon Cleese expertly demonstrates is that there are so many ways to walk, or run, a step forwards.
The Ministry of Silly Walks
This is because the human body has what is known as an abundancy in degrees of freedom. For running, this means that there are an infinite number of ways that we can move the different parts of our leg to achieve a forward’s step. This can be thought of as repetition of task outcome without repetition of movement execution (Bernstein, 1967). Whilst some of these movements may be more efficient than others, all will get us towards our goal of moving one step forward, and runners will utilise these different options throughout their run.
The Role of Movement Variability
But why would runners do this? Is there not a particular step pattern that runners would want to repeat over and over again? In fact, the opposite is actually true. Sportspeople, including runners, have repeatably been shown to vary the way in which they achieve the same task goal (Bartlett et al., 2007).
This variability between repetitions is thought to provide a protective mechanism from overuse injury. If a runner moves in a slightly different way for each step, then they will stress their muscles, tendons and ligaments in a slightly different way. This will prevent any one muscle, tendon or ligament becoming overworked, which is thought to be the cause of overuse running injury (Bertelsen et al., 2017). What is even more interesting is that changes in movement variability may occur in the lead up to a running injury and could therefore be used as a tool to predict injury before it occurs (Fonseca et al., 2020).
The Future of Movement Variability
I’ve recently started a PhD in the Sports Engineering Research Group at Sheffield Hallam University and will be investigating the relationship between different measures of movement variability and overuse running injury. Whilst most research into movement variability has been laboratory based, I will be utilising wearable devices to look at runners’ movement variability during their normal outdoor running. I am aiming to conduct a study monitoring the movement variability of runners and their injury status over time.
To learn more about Ben and his work, you can check out his SHU profile and follow him on LinkedIn.
References:
Bartlett, R., Wheat, J., Robins, M., 2007. Is movement variability important for sports biomechanists? Sports Biomechanics 6, 224–243. https://doi.org/10.1080/14763140701322994
Bernstein, N., 1967. The Coordination and Regulation of Movements. Pergamon, Oxford.
Bertelsen, M.L., Hulme, A., Petersen, J., Brund, R.K., Sørensen, H., Finch, C.F., Parner, E.T., Nielsen, R.O., 2017. A framework for the etiology of running-related injuries. Scand J Med Sci Sports 27, 1170–1180. https://doi.org/10.1111/sms.12883
Fonseca, S.T., Souza, T.R., Verhagen, E., Van Emmerik, R., Bittencourt, N.F.N., Mendonça, L.D.M., Andrade, A.G.P., Resende, R.A., Ocarino, J.M., 2020. Sports Injury Forecasting and Complexity: A Synergetic Approach. Sports Med 50, 1757–1770. https://doi.org/10.1007/s40279-020-01326-4