Your baby sister is powerful. Your grandad is powerful. We are all powerful. This is because power is the product of force and velocity (P = F x v) and all human movement is a mixture of these two variables. The gentle slow stroke of a mother pacifying a child, or the quick jab of a boxer, can be loosely termed power movements as they both have different contributions of force and velocity.
So where am I going with this? Well many of you are interested in making your athletes more powerful, which if you improve force and/or velocity capability, is relatively easy to achieve. Making people stronger (increasing force capability) is the focus of many resistance training programs as improving velocity capability is typically a little more difficult. However, I am going to propose that for many of you that improving power is not where it is at, rather improving explosive power, or the power per unit time is where your focus should be. For many of your athletes the power that they can produce in 100 milliseconds (sprinting)or 300-600 milliseconds (different types of jumps) for example, is the critical determinant of success i.e. the power per unit time or explosive power. To change/train this variable then, you need to understand how to measure it.
Since power is the product of force and velocity, collecting such data would intuitively make sense. Correct? Not really! Have a look at the stylised graphs in Figure 1, this type of data is great at showing us the effects of: 1) heavy - slow resistance training (force dominant); 2) plyometric training (velocity dominant). None of the curves, however, provide us any insight as to the explosive power capability or the power per unit time. So, where to next?
This makes a little more sense as we are looking at power per unit time and having force on the x-axis a contributor to power, and time on the y-axis, should provide the data we are looking for. Correct? Not really! What we are looking at in this graph is the peak force of two athletes, and the slope of the lines to the peak force is called their rate of force development (RFD). You can see the slope of Athlete A is steeper than Athlete B, therefore they are producing more force at 100 ms as compared to the other Athlete B. Athlete A produces more force per unit time, that is they have better RFD capability. However, RFD is not the same as explosive power. So often I see practitioners, mix RFD and power in the same sentence thinking that they are the same quality. They are not, power is the product of force-velocity data and RFD force-time data. They are distinctly different curves. So, where to next?
To measure explosive power ability, power-time curves are the data we need to be looking at. We have a pre-occupation at investigating force-time data (for good reason), however, if explosive power is of interest, then invest your time in the power-time curve. Of real interest is the rate of power development (RPD). How many times have you seen that measure reported in the literature? Not a lot methinks. So, if you are interested in improving the explosive power of your athletes then you would be interested in changing the steepness of the slope (RPD), and hence producing more power per unit time. In the example provided in Figure 3, Athlete A was tested initially (Pre) and after 6 weeks (Post) of training, RPD improved so that the athlete was producing more power in a time epoch (i.e. 100 ms in this example).
In sum, power is easy to change, increasing force capability is the focus of many programs, due to the easy gains via resistance training. However, explosive power rather than power might be the athletic quality that is most important for you to monitor in optimising the performance of your athletes. In this case power-time data/curves become very important and RPD is king! Not many people go here, so there is opportunity for practitioners, trainers, coaches and researchers to unpack this measure in more detail through the use of linear position transducers, accelerometers and/or force plates.
Over the next three-four posts I’d like to share with you some ideas for explosive power development. Until then – thanks for reading.
JC Online provides online physical conditioning education for physiotherapists, strength and conditioning coaches and physical therapists. If you have any questions about our courses and other resources, please get in contact with us using the email above.
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