Why “Lift X% of your 1RM for Y reps” isn’t always that helpful

Coaches prescribe a certain % of 1 RM to help clients choose a load for a set of reps. Like “Do 3 sets of 8 at 75% of your max”. Sounds scientific. But there’s a catch...

That % is based on your 1-rep max (the most weight you can lift once). But how many reps you can do at 75% depends on you, the exercise, and how fast/slow you move.

1. You - your training history matters. The more endurance-trained you are, the more reps you can do with a given % of 1RM. Think of it this way - 2 phones with 25% battery. One dies in 30 mins, while the other refuses to die. Same number, different endurance.

   
   

2. The exercise - some exercises are easier than others to do with a given % of 1 RM.

   
   

3. Lifting speed/ Tempo - You can perform more reps at a given % of 1 RM with a faster tempo than with a slower tempo.

If we combine these variables, the difference is stark.

Let’s say two people lift 70% of their 1-rep max. One's a marathon runner doing leg press at lightning speed. The other’s a powerlifter doing seated rows in slo-mo.

Guess what?
The runner might crank out reps like they’re doing laundry. The lifter? Might gas out halfway through their Spotify ad. Same weight. Same percentage. Totally different experience.

Why does this matter?

Muscles need to experience sufficient effort in order to adapt. If you stop too early, you don’t challenge them enough. If you push too far, you burn out.

So what do we do instead?

1. Test first, suffer later - test how much someone can lift for max reps (e.g. their 10-rep max, 3 rep max), then just subtract a couple reps to stay safe. So if they can leg press a small truck for 10 reps, you ask them to do 8.
   Basically: Find the edge. Now back off a little.

2. The “leave some gas in the tank” method (Reps in Reserve). You’re not testing anything. You're eyeballing it like Gordon Ramsay seasoning food. Stop when it feels like there's just enough pain left in the tank. Some people will hit 6 reps. Others, 10. Doesn’t matter. As long as they don’t hit full failure, we’re good.

3. Bar speed method. This gets fancy. Track how fast the weight moves. The slower it gets, the closer you are to failure. Once that bar starts moving like it's underwater? Time to stop. You're in the red zone.

Moral of the story?

Percentages don’t mean much without context. They are a starting point, not a law. Listen to your body, not just your spreadsheet. What matters is effort - the right signal. Whether you do that through rep maxes, reserves, or bar-speed radars is immaterial.