Sprint Performance: Metres or seconds; which is more important?
At the end of my first entry, I suggested that a focus solely on forces at the expense of technique factors can cause us to miss some important determining factors in sprint performance. This blog post will begin to expand on how some of those factors play a role.
Two of the most important values to sprinters are the distance they have to run (in this case, I will focus on the 100 metres) and the time that it takes them to do so, for instance 10.00 seconds. As biomechanists, we like to combine these two values into a measure of the speed of the athlete, so that we can analyse which technical aspects of the performance influence that speed and therefore the likely outcome. To do this, we simply divide the distance run by the time taken, so in this example, the average speed of our sprinter throughout the run would be a nice round 10 m/s (metres per second).
In order to investigate the factors that can influence this speed, we can break the sprint down into different phases (start, acceleration, transition, maximum velocity etc. — but that’s probably a topic for another post), and ultimately further into individual steps. It has been well documented, for example on the BBC , that Usain Bolt takes approximately 41 steps to complete 100 metres, but other elite males can take anywhere up to 50 steps to cover the same distance [1].
If we consider the speed of any one of those individual steps, it can be improved either by increasing the distance that it covers, or decreasing the time that it takes. That is to say, if we want to run faster, each step can either cover a greater distance in metres or have a reduced duration in seconds. However, it is difficult to make both of these things happen together. If we try to make a step cover more distance then it will tend to take more time, and if we try to make a step take less time then it will tend to cover less distance. This ‘negative interaction’ has previously been nicely identified and investigated by Dr Joe Hunter and his colleagues in New Zealand in performers from a range of sports [2].
Across the scientific literature, biomechanists interested in maximising speed have often investigated step length (distance covered in metres) and step frequency (number of steps per second, which gives us the ‘per second’ part of the speed measure). There have been studies of step length and frequency at the start of a sprint [3, 4] and at maximum velocity (including my own [1]), but few that have measured individual steps throughout a sprint [5]. This is undoubtedly due to data capture difficulties over 60 or 100 metres, but perhaps could be overcome in future with improvements in technology or systems like Optojump or inertial measurement units.
Within that scientific literature there are some consistencies, but also numerous contradictions, on the relative importance of step length and step frequency to sprint performance. In my next post, I will delve in more detail into those published findings in order to address the question I posed at the start of this post — metres or seconds; which is more important to sprint performance?
References
1. Salo, A.I.T., Bezodis, I.N., Batterham. A.M. & Kerwin D.G. (2011). Elite Sprinting: Are Athletes Individually Step Frequency or Step Length Reliant? Medicine and Science in Sports and Exercise, 43(6), 1055–1062. doi: 10.1249/MSS.0b013e318201f6f8.
2. Hunter, J. P., Marshall, R. N., & McNair, P. J. (2004). Interaction of step length and step rate during sprint running. Medicine and Science in Sports and Exercise, 36(2), 261–271. doi: 10.1249/01.MSS.0000113664.15777.53.
3. Bezodis, N. E., Salo, A. I. T., & Trewartha, G. (2015). Relationships between lower-limb kinematics and block phase performance in a cross section of sprinters. European Journal of Sport Science, 15(2), 118–124. doi: 10.1080/17461391.2014.928915.
4. Slawinski, J., Bonnefoy, A., Leveque, J. M., Ontanon, G., Riquet, A., Dumas, R., & Cheze, L. (2010). Kinematic and kinetic comparisons of elite and well-trained sprinters during sprint start. Journal of Strength and Conditioning Research, 24(4), 896–905. doi: 10.1519/JSC.0b013e3181ad3448.
5. Nagahara, R., Naito, H., Morin, J. B., & Zushi, K. (2014). Association of Acceleration with Spatiotemporal Variables in Maximal Sprinting. International Journal of Sports Medicine, 35(9), 755–761. doi: 10.1055/s-0033–1363252.
