L’électron libre

Here’s the deal, you push a chest press, say 70kg, you reach fatigue at 8 reps. You change gym, different chest press, same weight:70 kg, FIVE reps to fatigue, What the hell ???

Or…you’re in competition with a friend of yours (friendly competition is good, it provides motivation and results), he tells you his performance on his machine…how does that convert into a performance on your machine?

Well, yes, workout machines are very different from a brand to another, from a model to the newer model of the same brand. Worse, sometimes they don’t even show the unit (Kg or Lbs?), worse even more, the numbers sometimes mean neither Kg or Lbs, just numbering the iron plates.

If you use machines, as soon as you change gyms you’re in trouble when it comes to tracking performance.

The following presents a method to convert any performance to what it would be on a another machine or with free weights. The only hypothesis is that the exercises used in the conversion solicit the same muscle groups.

If used to convert a performance from a machine to free weights, this method provides a universal measure of performance.

This post will include an example of use soon.

HOW TO OPERATE?

In the following, mach1 and mach2 will be the names of the two different machines allowing to exercise the same muscle group in a very comparable manner.

STEP ONE: FIGURING OUT THE CONVERSION RATES

• Use the two-set method on a given machine (mach1) to assess your performance on it (say a chest press). Calculate the two coefficients (a_1 and b_1) that represent your performance on this machine. The details of how to use the two-set method to obtain these coefficients are presented on this page.
• After some rest (~4/7 days), do the same on the other machine (mach2). You get two coeffients, a_2 and b_2.
• Calculate the conversion rate from mach1 to mach2, therefore k_a= a_2/a_1, similarly k_b= b_2/b_1.

STEP TWO : USING THE CONVERSION

• Everytime you want to convert your performance, you will need to go through the two-set method on the CURRENT machine you use (mach1). You therefore have a and b for mach1, not necessarily the same as those you had the day you established the conversion rates.
  

———————————————————————-

SKIP THIS IF YOU HATE MATHS
The equivalent performance on mach2 (the reference) is given by :

becomes by conversion:

———————————————————————-

Just fix either x2, meaning the number of reps (resp. y2, the weight) for mach2 and the equation yields you the corresponding weight (resp. number of reps). In other words, you have the equivalent performance :

By fixing reps (x_2) you get the equivalent weight:

OR

By  fixing weight (y_2) you get the equivalent number of reps:

EXAMPLE OF USE

Coming soon