How to fine-tune your exercise prescription to train harder
By Strength Sensei CP
Publication Date: 2008
I’m often asked why I prescribe a repetition range in many of my workouts, such as 4 x 6-8. Why not 6 reps, or 7 or 8? And why don’t I use percentages of the 1RM (1 repetition maximum) that weightlifters use? Let me explain.
First, unless you are a competitive weightlifter, I am not a fan of using percentages. One reason is that muscles have different fiber types. Let’s say I want an athlete to do the leg press and the seated leg curl, and I prescribe a weight that equals 92.5 percent of their 1-repetition maximum. Using a standard percentage/rep conversation chart, you would expect the athlete to perform about 3 reps in both exercises. Not quite.
The quadriceps are primarily Type IIa muscle fibers (slow-twitch), whereas the hamstrings are primarily Type IIb muscle fibers (fast-twitch). The Type IIb fibers can produce stronger contractions than the Type IIa fibers, but the Type IIa fibers have more endurance. As such, this athlete might be able complete just 3 reps in the leg curl but can crank out a dozen reps in the leg press.
There are many excellent resources listing the fiber types of specific muscles, such as La Forza Muscolareby Carmelo Bosco, Ph.D. The problem is that neurological efficiency changes with training age. Using our example of the leg press, a beginner might perform 12 reps with that 92.5 percent weight, but after two years of training, those max reps at that percentage may drop to 10.
Training age affects an athlete’s neurological efficiency, such that they respond better to lower reps (This photo by Ryan Paiva @liftinglife; lead photo by Miloš Šarčev)
Another issue is that percentage systems lock you into weights that may be too heavy or too light for a specific workout. Let’s face it, some days everything feels heavy, such that there is no chance you can complete the prescribed weights at those percentages. Other days you feel amazing, and those weights are too light such that you easily complete all your prescribed reps and sets. In both cases, the quality of your workout is compromised.
The practical solution is to let the repetitions determine the load. Rather than 3 sets x 10 reps at 75 percent of 1RM, you write 3 x 10. You can use those percentage conversion charts as a starting point for beginners, but athletes need to keep accurate records so they can determine the best weights to use for every set.
Refining this suggestion, rather than writing a single repetition prescription for a set, prescribe a repetition range. The reason is accumulative fatigue affects performance. If the weight you use on your first working set barely allows you to complete 8 reps, you might only manage 9 or 8 reps on subsequent sets. Not being able to complete all the prescribed reps breaks you down mentally. Rather than 3 x 8, a better exercise prescription would be 3 x 6-8. If you somehow managed all 3 sets at 8 reps, great. If you hit 8,7,6 reps, still great!
There is a place for percentage systems in weightlifting, but using rep ranges is the most practical way to get bigger and stronger.