A sprinter has a personal best of 10.31 s for the 100 m, but needs to run at least 9.90 s to be internationally competitive. How can we use our knowledge of biomechanics to bring about an improvement in running performance?
By the end of this chapter you should be able to:
•Describe a process by which you would design a biomechanics testing programme
•Describe a process by which you would integrate biomechanics testing into a complete training/testing programme
•Draw a deterministic model of a sporting task or movement
You now have all the theoretical knowledge to apply biomechanical principles to the optimisation of human movement. But as you’ve noticed while reading the ‘Interview with the Experts’ sections, the development of biomechanics testing regimes and their integration into a complete (including physiological, medical, psychological) programme has its difficulties. What follows is a basic step-by-step method by which you might be able to design a programme for yourself.
FIVE-STEP METHOD FOR BIOMECHANICAL INTERVENTION
In order to improve running performance, we can use a step-by-step method similar to the one presented below, although you might put your own spin on it.
Step 1
Determine which part of the race requires the most improvement. Before we try to change anything we have to know what we would like to focus on. Each part of the race requires a different technique (e.g. starting vs. top speed) so we have to know the object of our programme. To do this we can perform a race analysis. Using force sensors in the starting blocks and timing lights on the track we can find out the reaction time and running time through different phases of the 100 m race. We might find, for example, that the reaction time and time to 40 m is comparable in the best athletes, but that the athlete’s top speed (e.g. time between 50 and 70 m) might not be as good. We’d expect then also that their speed in the concluding phase of the race would also be lower than their opponents because, as we saw in Chapter 1, the deceleration phase is influenced by the top-speed phase.
Step 2
Conduct a biomechanical (kinetic and kinematic) analysis to determine technique flaws in this phase of the race. By focusing on a particular part of the race we are able to place video cameras and ground reaction force recording equipment (e.g. force platforms) in the right place (e.g. at the 60 m mark) to capture the necessary detail. We would then need to determine which performance variables (i.e. technique factors that can vary between athletes) are of most interest. One way to determine which performance variables are worth monitoring is to write down the physical principles that you know might influence performance. As an example, my list would be:
1.Understanding velocity and acceleration: we need to know the velocity curve of the sprinter.
2.Action–reaction (Newton’s) law: we know that the magnitude and direction of the applied ground reaction forces will influence the acceleration (and therefore speed) of our athlete. If the forces are not appropriately developed, the athlete will not run fast (Chapter 5).
3.Arm and leg length during the running stride: remember, if our arms are extended then their moment of inertia will be greater and their angular velocity will be slower, even if our forces (well, our torques) are well applied (Chapter 8). As we also saw in Chapter 7, we need the knee to flex appropriately during the leg’s recovery phase in order to decrease its inertia and increase stride frequency.
4.Conservation of angular momentum: as shown in Chapter 8, it is important that the arms and legs move in unison so that rotations in the body are cancelled and running efficiency is optimised.
5.Centre of mass location: if the centre of mass is too far in front of the body we will tend to over-rotate and therefore deliver ground reaction forces inappropriately. If our centre of mass is too far back, we will find it impossible to run forwards. Very importantly, as we saw in Chapters 5 and 18, we tend to apply a braking force as the foot first contacts the ground. If the distance between our foot contact and centre of mass is too great then the braking force will be exaggerated.
Once we have written down these performance variables we can determine which exact variables we want to study. For example, we might measure the horizontal vs. vertical ground reaction force at various points in the stride (point 2), elbow and knee angles at various points in the stride (points 3 and 4), and the location of the centre of mass and its horizontal distance from the foot–ground contact point (point 5). By using our knowledge of biomechanics, we will then be able to alter the athlete’s technique to try to improve performance.
Another method of figuring out which variables are worth recording is to develop a deterministic model (see Fig. 19.1). A deterministic model is essentially a flow chart that shows which biomechanical factors most likely determine performance. For sprint running a typical diagram might look like this:
Fig. 19.1
In some cases you might choose to become more quantitative in your modelling. For example, the speed of release might be modelled like this (Fig. 19.2):
Fig. 19.2
By taking this extra quantitative step, we can see that the ground contact time becomes important, but, in opposition to many coaches’ ideas, a longer ground contact time should lead to a greater impulse and thus a faster running speed. If we look at the same line in the model, though, we can see that if the braking force is too great then the average horizontal force (and impulse) will be reduced. We know that this happens when the foot lands too far in front of the body’s centre of mass, so it’s only useful to increase ground contact time if other factors such as the braking impulse aren’t affected too much. Ultimately, the optimum case will be found through rigorous and continued testing of our athlete.
Step 3
Test the athlete’s personal characteristics. Remember that the biomechanical testing is only one part of a whole programme. As you’ve read in the ‘Interview with the Experts’ sections, the best biomechanists understand how to fit biomechanical testing into the bigger picture. It is possible that technique flaws are related to strength, flexibility or muscular endurance issues, coordination difficulties or psychological issues (for example, the technique flaws might occur only when the athlete is nervous or stressed). You will need to compare your findings with those of others in order to determine the best way to improve your athlete’s performance.
Design a plan to improve technique and other parameters. You will need to determine which technique flaws should be worked on first, and whether technical improvements need to be coupled with improvements in strength, flexibility, muscular endurance, psychological state, etc. A good biomechanist also determines the best way to show the coach and athlete what flaw they have found, and discuss with them both how and why they think it should be redressed; good, clear communication is the key to this step.
Step 5
Make a plan for re-testing. It is impossible to learn or modify a task without feedback, so your job is to continue to provide feedback in the most appropriate way (e.g. simple information often, or more detailed information less often, or both). Consider a darts player trying to improve their accuracy. It could not be done if they could never see whether they managed to put the dart where they intended. It’s the same for an athlete. If they don’t know whether they’ve achieved a technique they’ll never be able to perfect it.
Of course, this five-step process can become more difficult when other factors influence the optimum technique. For example, improving rowing technique requires a good knowledge of the leverage associated with the boat’s rigging and the influence of oar design on the hydrodynamics, and force application profile, of the oar. In this case, the athlete and the system (i.e. the boat) need to be considered together.
THE ANSWER
As you have seen, the answer to this question is well described above. You would make a five-step plan, ensuring that you use your biomechanics knowledge to optimise performance. A detailed plan is very important in order that the most influential biomechanical flaws are noticed and corrected. Once you have examined the weakest phase of the sprinter’s race (which was the top-speed phase in this example) you could then work through the starting and deceleration phases. You would provide continuous feedback to the coach and athlete in order to continue to improve (or maintain) the athlete’s technique and performance, and you would record how the biomechanical changes tended to change running times.
HOW ELSE CAN WE USE THIS INFORMATION?
Such a plan can be used for many athletes, although the important biomechanical concepts might change. For a swimmer, for example, you would have to consider some similar principles, such as velocity/acceleration, action–reaction (Newton’s laws) and conservation of angular momentum, but you would also have to consider wave, form and surface drag, Bernoulli’s theorem and pressure gradients, the dynamics of lift and others. You can also use a similar process to improve the performance of children who are learning a new skill, with injured or disabled patients who are re-learning activities of daily living, or with workers learning a new occupational task. Ultimately, a comprehensive process, which also includes input from other scientific disciplines such as physiology and psychology, can be used to optimise performance in any human pursuit.