Here's a quick and easy way to compare strength levels between individuals of different body weights. It’s commonly referred to as the two-thirds power rule and is an improvement on the more commonly used methods out there. I first came across this formula when I was reading through some of Dan Bakers' work, all of which I highly recommend (http://www.danbakerstrength.com). More recently, Dr. Greg Haff's work on monitoring brought it back to my attention.

Generally speaking, aside from the obvious absolute strength comparison (e.g. You lifted 120 lbs; I lifted 100 lbs. Therefore, you're stronger), the only other widely used comparison is the relative strength values, which are calculated by weight lifted/body weight (e.g. 200kg/100kg = 2 versus 150kg/70kg = 2.14). In this case, the lighter individual is classed as relatively stronger than the heavier individual because he can lift more weight per kilogram of body weight. However,  this is obviously the case. Lighter people will always be stronger relative to their body weight. Is this actually the case though? Are they actually stronger?

We know that the capacity for producing force exponentially decreases with additional body mass. The world record clean and jerk in the 105-kg class is 263 kg. This equates to an impressive two and a half times body weight. But when compared to the 56-kg class record, which is 168 kg, you can see that the lighter man has the better relative strength—over three times body weight! When we do max testing in my gym, the lighter guys always win the contest when you examine the results from a relative point of view even though the heavier guys always lift more weight. But who do the bragging rights really belong to? Hopefully, this method will settle the argument once and for all.

The two-thirds power formula is a handy method for comparing the two lifters to decide who is actually stronger. Here’s an example. In the first instance, the lighter individual is relatively stronger than the heavier individual with a 2.14 times body weight lift versus a two times body weight lift. But we know that lighter individuals are always going to be relatively stronger than heavier individuals, so using the two-thirds power formula, we can determine who is actually the strongest.

The formula is as follows:

Don’t get concerned about the math element to this. You really don’t need to have a math degree to figure it out. All you need is a calculator with a 'power to' button. All scientific calculators have one!

Using the example above, the figures are inserted into the formula (I've started with the heavier individual first):

This gives us the value of 9.14, which is the multiplier for the comparison between the lifts. Using this multiplier, we can see that the formula for the 70-kg individual is:

So the value that the 70-kg individual needs to lift is unknown, but the formula can be rearranged very simply to calculate:

The value comes to 157 kg. So in the example shown, the heavier individual is the strongest. The lighter individual would need to lift an additional 7 kg to be equally as strong.

For maximal strength lifts, you can use this formula to compare lifts with more accuracy than the relative strength comparison. This formula is also really handy for strength and conditioning coaches when comparing workloads during training blocks for the same individual and between athletes of different body weights. Just insert the number of reps and sets into the formula and work it out the same way. You can compare men with women as well using this formula, but it may be slanted slightly due to gender differences. Don’t be put off by the math. It's like a strength and conditioning version of brain training to keep you younger for longer while improving your programs.

That's all for now. My brain is fried from all this. Keep training hard and let me know if you found this useful.

Brendan Chaplin is the CEO and founder of Strength and Conditioning Education, the UK's largest S&C coaching and training company. You can reach Brendan on all social platforms @brendanchaplin where he will be happy to answer your questions and take your feedback.