The Effect of High Rep Training on Strength and Size
In a recent research study(1) a group of researchers set out to explore the impact of lighter weight and higher rep training on muscle mass and function. They designed a study “to compare the adaptive changes in muscle size, contractile strength, and MHC (fiber type) composition evoked by resistance training performed at either low or high contraction intensity (i.e. low or high reps) while equalized for total loading volume”
Specifically, this study compared 10 sets x 36 reps using 15.5% 1RM to 10 sets x 8 reps using 70% 1RM. The study ran 12 weeks, with 3 workouts each week.
How did the 10×8 program do? It produced a 7.6% increase in muscle size (hypertrophy) and a 35% increase in 1RM (one rep maximum).
Not bad. Not bad at all. And, candidly, not the least bit surprising. Heavy weights and low reps has long been the accepted way to maximize strength and size.
How about the 10×36 reps program? Many would predict that such a “high” rep range would build endurance and, if it didn’t cause an outright decline in strength and size, would surely not increase strength and/or size. Remember, standard physiological and training wisdom is that more than 20 reps is “endurance” training and endurance training does not increase strength and size. This belief is reflected in the following quote I read on a bodybuilding forum. “Anything beyond 20 reps is high, and not good for strength gains”.
Anyone who would predict that high reps are good for endurance only would be wrong.
The 10×36 program produced a 19% increase in 1RM and a 2.6% increase in muscle size. Pretty impressive for a program many would call “endurance training”.
There are a couple of things to be learned from this study. First, this study clearly shows that a program consisting exclusively of heavy weight and low reps produces greater increases in strength and size than a program consisting exclusively of lighter weights and higher reps. This isn’t any sort of surprise – research over the past 80 years has very consistently shown this same thing.
But there is more to the story than just heavy weights and low reps wins. The most glaring point to consider is that “high” reps increased strength levels 19% and muscle size 2.6%. This naturally brings up two questions. Is this the only study that has shown “high” reps increase strength and size? And from a physiological standpoint how do higher reps cause strength and size to increase?
There have been multiple studies comparing changes in strength and size from different rep ranges and, despite what conventional wisdom teaches, these studies have consistently shown that higher reps cause increases in both strength and size. Yes, heavy weights and low reps increase strength and size the most. But that doesn’t mean higher reps don’t also build strength and size. Conventional wisdom has incorrectly interpreted the research as “heavy weights and low reps build strength; light weight and high reps build endurance”. The first lesson from the research is that “light weights and high reps do increase strength, just not as much as lower rep schemes.”
It is important to note that the research has shown that the higher the rep range the smaller the increase in strength and size. So while reps in range of 25- 35 can build strength an impressive amount, the higher above this that you go the smaller the increases in strength.
There is no getting around the fact that a program of only heavy weights and low reps builds significantly more strength and size than a program of only lighter weight and higher reps. So if you are trying to decide what reps you should exclusively be doing, pick reps less than 20. But, this study also clearly shows that that conventional strength training thought is inaccurate to some degree. Higher reps do increase strength and size.
This brings us to the second question. What logical explanation can we come up with to explain these results? By what physiological mechanism could high reps build strength?
The most logical answer is that what conventional physiological and training wisdom call “high” and “endurance” really aren’t particularly “high”, nor are they really “endurance”. It appears that “high” and “endurance” start somewhere far beyond 20 reps. Exercise doesn’t suddenly transform from “strength” to “endurance” within a matter of a few reps. Going from 12 reps to 24 reps in the same exercise doesn’t somehow turn the exercise into an “endurance” workout. Instead, strength and endurance exist on a continuum, with both elements being trained at all reps. Training at the strength end of the continuum, training between 1-15 reps, increases strength the most and endurance the least. As you increase the number of reps strength is less affected and endurance is more affected, until at some point you are doing so many reps that changes in strength are no longer measurable. That point happens somewhere above 150 reps, according to the research.
What the research hasn’t told us is how higher reps built strength and size. What physiological mechanism is at play that causes higher reps to build both strength and size? If there are different physiological reasons for how low reps build strength and how higher reps build strength, then it raises a fascinating question. What if you combined low reps with higher reps? What would the results be? If different physiological mechanisms are responsible for the increases in strength and size at different reps then would a combination program of different reps result in better results than single rep programs? As we have seen higher reps do increase strength and size and if they build strength due to a different mechanism than lower reps there may be some advantage in combining lower rep training with higher rep training.
This study doesn’t answer the question but this one does. In the meantime, the point is that light weight and high reps are not really “endurance” exercises; high reps are both strength and endurance training and the degree to which they affect strength or endurance depends on the number of reps being performed.
Holm L, et al, Changes in muscle size and MHC composition in response to resistance exercise with heavy and light loading intensity, Journal of Applied Physiology, Nov 2008, 105:1454-1461