Analysis of Power Outputs in the Clean Uncovers New Information
If you’ve ever seen those graphs of power outputs that show how much power is generated during each part of an exercise, then I’m sure you’ve imagined up some ways to use this information. If you’re anything like me, you also get a nerdy thrill at the idea of combining math and physics with the exercises we do all the time in the gym.
What you might not be aware of, however, is that the common methods of measuring this output might not give you the total picture. Sure it shows you where the power needs for each exercise are the highest, or lowest for that matter, and probably shows you the most common sticking points that we face, but perhaps we could get more out of these charts with more sophisticated methods. In a study published this month in the Journal of Strength and Conditioning, researchers looked to compare the various methods measuring power output.
One good reason to compare power measuring methods is to examine the differences between them. This might seem trivial at its surface, but knowing the difference can tell you which graph might be best for your purposes. In fact, the traditional methods for measuring power output are great for barbell lifts, but might not be as good for other types of athletic movements.
The traditional methods involve measuring the force an athlete puts into the ground, called ground reaction force (GRF), or the movement of the barbell or other implement. This sounds complicated, and the analysis of it can be very complex, but think along the lines of bouncing up and down on your bathroom scale. Notice that the needle goes up and down, sometimes less than your weight and sometimes more. This is essentially GRF.
One method that is not very common at all is to measure the forces at each joint. This method is less common because it is both expensive and time consuming to do right. However, I’m sure I don’t have to tell you why this information might be important.
In this newest study the researchers compared all of these methods for examining one of the Olympic lifts, the clean. Not only did they look at each method, they also used various loads that were at fixed percentages of each of the participant’s maximums.
The researchers discovered some interesting tidbits. The number of correlations between the traditional methods and joint methods increased as the weight got higher, topping out at 85% of the participants’ maximum. This means most likely that technique is best above 85% of the max, and the power generated by the joints is most effectively transferred to the bar. This also supports the use of the traditional power measurements for heavy barbell movements, as they line up nicely to the joint power. For exercises that do not demand maximal power, however, measuring joint power output is likely a better way to determine how best to prepare for a sport.
The other, more obvious information we get from examining the joints individually is that they do not share power evenly. For example, the hips and knees actually had the highest power outputs at 75% of 1RM, whereas the ankle had its highest at 85%. Less surprising is that the hips peak early in a clean, whereas the knees and hips peak just before the end.
This type of data can give us a more detailed picture of where our sticking points and weaknesses originate, and will also provide the most accurate information for more complex activities. I look forward to seeing more if this sort of data in the future.
1. Kristof Kipp, et. al., “Correlations Between Internal and External Power Outputs During Weightlifting Exercise,” Journal of Strength & Conditioning Research, 27:4 (2013)
Chart courtesy of Jason Lake, from "Biomechanics and Newton's Law: Force-Time Curves and Human Movement."