Why can you do 250 pounds on the leg press at your usual gym but only 200 pounds when you go somewhere else in town? You didn’t suddenly get weaker, and contrary to popular myth, it’s not because the gym was lying to flatter you. Machines are just different.
Machine design is important
Let’s take the leg press as an example, as almost every gym has one. This is the machine that you have some sort of seat and platform for your feet on. You push with your legs to either move the platform while the seat stays in place, or vice versa.
There are many different ways to build this type of machine. Some are vertical, with your feet just above your hips. Some are horizontal. For some, the seat slides up a ramp, pulling weights on a stack. Each of these is a completely different machine, and it should come as no surprise that the one with a slope and weight stack is calibrated differently than the one where your feet are over you and you load weight plates on it.
Think back to Elementary school physics for a minute. When a machine has a lever arm, like a shoulder press, the length of the arm changes the degree of mechanical advantage (or disadvantage) you have in lifting the weight. The number of pulleys and cables in a cable machine can also change the force required to move the weight stack. When weights move on an angled path, the steepness of the angle affects how easily the weights move.
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And even when you compare two apparently identical machines, there can be subtle differences. One might be better lubricated than the other so that its parts can slide more easily. They cannot be exactly the same either; Perhaps the manufacturer moved a pulley to a different location between the 2018 and 2019 models. You have the idea.
By the way, machines are not to be equated with dumbbells. Just because you can squeeze X pounds on your legs doesn’t mean you can put a barbell on your back and do the same amount of squats.
So are the numbers meaningless?
Not at all. Only the numbers matter on this machine. If one of the plates in the stack says 50 and the next plate below it says 55, then you know that you are stronger if you can repeat the 55 than if you could just do the pin at 50.
When visiting a new gym, go by feel. If you could do eight reps on the 55 pin at your old gym, find a weight that could do eight reps on the new machine. It doesn’t matter what number is on that weight or how much the stack of weights would weigh if you could pull it out of the machine and place it on a scale.
Think of it like game currency: you wouldn’t waste time Googling how many Monopoly Dollars are equal to how many are equal Robuxbecause there is no reason for either of them to ever measure each other meaningfully. Everyone is useful in their own world and nowhere else.
So yeah, be sure to put these numbers in yours Training diary. They help you track your progress. But don’t expect them to be the same on another machine across town.
