One benefit of weight training is that everything is measurable - the weight of the bar, the weight of the plates we put on the bar, and the amount of weight our body can withstand to push or pull. We know this as our output or, more commonly, strength. The most effective way to measure our strength, and increase it, is by determining our one repetition max.
Take, for example, a back squat. The movement is like getting up from a chair while a weight sits on your shoulders.
If we wanted to calculate a one repetition max for this movement, we would continue to add weight to the movement until you could not stand up anymore. If we try to go straight for the heaviest weight, it would overload your central nervous system and we would fail. Your brain would say, ‘Mayday! Mayday! That’s too heavy. Get to safety now!’
Depending on your comfort level with the movement, we increase the weight with “big” jumps or “little” jumps. “Big” and “Little” are subjective to the athlete. Some athletes prefer bigger jumps with more rest between reps and some prefer smaller jumps between reps with little to no rest in between. A big jump for a lower body movement can be anywhere from 10 to 30 pounds while a little jump can mean 2 to 20 pounds, it is all based on your preference as the athlete.
I like to follow a lower body rep scheme for new athletes that looks like this:
1st SET - 15 reps at bodyweight or light weight as with just an empty bar
2nd SET - 10 reps at 10 to 30 pounds more than the 1st SET
3rd SET - 5 reps at 10 to 30 pounds more than the 2nd SET; since this is half the reps of the 2nd set, it could warrant a larger increase in weight for this set
4th SET - 3 reps at 10 to 30 pounds more than the 3rd SET; again, gauging the intensity based on how the 3rd set felt.
5th SET - 1 rep at at 10 to 30 pounds more than the 4th SET; since we have a lot of work under our belts at this point, might be best to do a smaller increase in weight from the previous set so as to not top out right away and give your muscles time to process the additional force needed to move the weight.
6th SET - 1 rep following the same guidelines in the previous SET.
Continue performing sets of 1 rep while adding regular increments in weight until you fail. The weight of your last successful set becomes your one rep max for that movement.
So now, the question becomes, why find your one rep max? The best answer is that it allows you to train with an intensity suitable for you and your current level of fitness.
For example, if I say to you, “we are doing 3 sets of 15 reps at heavy weight.” What does heavy mean to you? For one person, “heavy” might mean 15 pounds, but to another “heavy” might mean 50 pounds. Knowing your one rep max, I can say, “we are doing 3 sets of 15 reps at 80%” and we can calculate exactly how much that should be for you.
Knowing your one rep max ensures you train at a level that is appropriate for you and your fitness goals. It is a measure of your current strength and should increase as you progress in your fitness journey.