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cfilipov / MuscleBook

[ABANDONED] Muscle Book is an iOS workout tracker for strength training and body building.
GNU General Public License v3.0
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Inverse of e1rm #23

Open cfilipov opened 8 years ago

cfilipov commented 8 years ago

It might be useful to have the inverse of e1RM. That is, when doing pull ups for example, if you did 10 pull ups at a 166 lbs bodyweight, it would be nice to compare the equivalent number of reps at your new (higher or lower) bodyweight. The e1rm does this by normalizing to 1 rep, but I'd like to see if this can be done by figuring out by normalizing the weight.

JonathanGuberman commented 8 years ago

If the question is "can this be done," the answer is definitely yes. It looks like you're using Brzycki, but the process should be roughly the same for any of them. Set the 1RM max at the new weight and reps equal to the 1RM of the old weight and reps, then rearrange the equation to solve for new reps. It gives you: new_reps = 37 - (new_weight*(37-old_reps))/old_weight It seems to work; for example, if I use 100 for old_weight, 8 for old_reps, and 110 for new_weight, the equation gives 5.1 reps at the new weight. If I plug those numbers in here, it says that 8 reps at 100 and 5 reps at 110 are both equivalent to a 1RM of 124.

You could do the same equivalence and solve for new_weight if you wanted to figure out how many reps you should be able to do at a given weight, based on how many reps you can do at a different weight.

cfilipov commented 8 years ago

What would you call this field? I was thinking "Estimated Reps" or "Normalized Reps". I'm leaning toward the later.

JonathanGuberman commented 8 years ago

"Predicted reps"?