Prior to the 1940s, most medical doctors believed that weightlifting was bad for your health; that it damaged your heart. But it's not that they specifically singled out lifting weights as potentially damaging to your ticker. Nah, they were pretty much against any type of extreme effort.
Hell, it's a wonder we beat the Nazis: "Go over and fight the bastards, but take plenty of breaks and for heaven's sake, don't do anything strenuous."
Enter Thomas Delorme MD, who was himself a weightlifter. In contrast to the other medicos of the time, Delorme believed weightlifting could help rehab injured World War II soldiers. He got a chance to prove it in 1944 when Sergeant Thaddeus Kawalek limped in to see him for help with his bum knee.
Fortunately, Kawalek was a like-minded soul. Not only did he lift weights, too, but he also believed in Delorme's theories about the restorative and rehabilitative benefits of resistance training.
If you were directing the historical docudrama of Delorme's career, this is when you put together a training/rehab montage and queue the choir of heavenly angels because weightlifting made Kawalek's knee get better a lot faster than other patients with a similar diagnoses. He ultimately regained full use of his knee.
This story was one of the specific occurrences that led Delorme to come up with his philosophy of weightlifting, a philosophy most of us practice to this day and refer to as the science of progressive overload.
In general terms, the following is the foundation Delorme laid out, something every lifter learns pretty fast if they're at all serious about their sport. It's what we call the "repetition continuum":
- Low reps and heavy loads (1 to 5 reps per set using 80 to 100% of 1RM) optimize gains in strength.
- Middle-of-the-road reps (8 to 12 reps per set with 60 to 80% of 1RM) are best for hypertrophy.
- High reps (15 or more reps using loads below 60% of 1RM) are best for building muscular endurance.
That's weightlifting gospel, right? If lifting had its own 10 Commandments, the preceding would be three of them, smack dab between "thou shall not tie up the squat rack by doing biceps curls" and "thou shall not wear loose underwear that allow people to see your balls when you bench press."
But there's a heretic in our midst, four of them really, and one of them is former T Nation contributor and strength-training research machine, Brad Schoenfeld.
So cinch your weightlifting belt a little tighter and get ready for a jolt because Schoenfeld and his colleagues' latest paper – "A Re-examination of the Repetition Continuum" – suggests that the body of research on the subject fails to back up what Delorme laid out all those years ago.
In fact, after looking at all the pertinent research, Schoenfeld et al. note that the evidence for all those rep ranges is really weak and they all work pretty much the same for building strength and growing muscle (as long as you adjust volume).
Furthermore, they note that the evidence for how we normally train for muscular endurance really doesn't pan out at all.
What the What?
Let's take a brief look at what Schoenfeld and associates said about each of the adaptations supposedly targeted by the repetition continuum:
1. Strength (1 to 5 reps)
Before you get all crazy, Schoenfeld admits that the meta-data "shows a clear advantage to using heavier compared to lighter loads when the number of sets are similar between conditions."
However, the research is filled with examples of significant strength gains being made with very light loads (over 20 reps per set). Of course, there's a "dose-response" relationship in play between load and strength gains. In other words, you'd need to do a lot more reps with light weight to approximate the strength gains seen in those training exclusively with high loads.
This might not be as true, though, when lifters approach their "genetic ceiling." These individuals might need to consistently train closer to their 1 RM.
Still, it's murky. Schoenfeld reminds us that, "...an important point to consider is that researchers generally carry out 1RM testing on exercises performed as part of the interventional program." In other words, studies on strength gains do their testing on the same exercises used in the actual study. This may give skewed results.
Schoenfeld himself did a study where subjects used heavy loads on traditional exercises and were then tested on an isometric device instead of the same exercises they'd used during the study. The subjects proved to have gained strength alright, but the gains were small and statistically insignificant.
Keep in mind that while Schoenfeld and company aren't by any means trashing the concept that heavy loads lead to superior strength gains, they are saying that there's some ambiguity.
2. Hypertrophy (8 to 12 reps)
Bodybuilders pretty much have all their mail sent to the 8 to 12-rep zone. The trouble is, most of the research that weakly supports this rep zone comes from studies on the hormonal response to lifting. Sure enough, study after study shows that mid-range training leads to hormonal spikes, but unfortunately, tiny, transient hormone spikes don't do much to enhance a physique.
Other studies show an increase in muscle protein synthesis (MPS) from mid-range training (while showing that the use of heavy loads can impair MPS), but Schoenfeld sees a problem: "Indeed, evidence shows a lack of correlation between acute post-exercise MPS measures and chronic increases in muscle mass."
And, when looking at all the research across the board, Schoenfeld found no difference in muscle hypertrophy between comparing high loads (over 60% of 1RM) versus low loads (less than 60% of 1RM).
However, as was the case with strength as an adaptation, volume seems to play a pivotal role: low loads can lead to the same or comparable degrees of muscle as using medium-load weight, but it requires more reps and more total volume.
3. Muscular Endurance (15 reps or more)
It makes intuitive sense that doing a lot of light-weight reps would increase your muscular endurance, but some research has shown contradictory results where medium-load reps resulted in greater gains in muscular endurance than low-load reps.
And, if there was a positive correlation between high-reps and muscle endurance, it seemed to be more relevant to the lower body than the upper body.
Unfortunately, most of the studies used a fewer number of sets for the light-load testing than what was used for medium-rep testing. It makes you wonder if the results would have leaned more in favor of high reps for endurance if they'd used an equal number of sets instead of using an equal amount of total load.
Viewed collectively, Schoenfeld concludes that the body of research shows that high-rep and medium-rep training show similar increases in muscular endurance.
What the Hell Do I Do Now?
Okay, so there's no ideal hypertrophy zone. That's no reason to fret. This info should be seen as liberating because you're now free to use a wide variety of rep ranges to achieve your goals.
Schoenfeld does admit, though, that the use of moderate loads might still be the most efficient way to train. Consider that light load training involves doing lots and lots of reps, which leads to spending a longer period of time in the gym. Training with light loads and high reps can also lead to metabolic acidosis "that can cause discomfort."
Regarding heavy loads, that type of training also requires more time spent in the gym. It's also harder on the joints.
Maybe the best answer is, as Schoenfeld suggests, "combining load ranges as part of a structured resistance training program." Of course, they'd take away his PhD badge if he didn't add the obligatory note: "...further study is needed to draw stronger conclusions on this topic."
Related: Reps Don't Matter
- Schoenfeld, Brad J, et al. "Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re-Examination of the Repetition Continuum," Sports, 2021, 9, 32.