What Does The Research Say?
Ask the average bodybuilder how to build muscle and they will give you the standard training prescription:
A moderate-to-high repetition scheme in the 8 to 12 range with moderate loads (60 to 80 percent of the 1RM) to optimize muscle gains.
This approach for “hypertrophy training” fits into a generally accepted “repetition continuum” that goes like this:
- Low reps and heavy loads (from 1 to 5 repetitions per set with 80 to 100 percent of 1RM) is used to train for strength.
- Moderate reps and moderate loads (from 8 to 12 repetitions per set with 60 to 80 percent of 1RM) is used for hypertrophic gains.
- A high repetition scheme with light loads (15 plus repetitions per set with loads below 60 percent of 1RM) is recommended muscular endurance.
This continuum is pretty much gospel in the strength and conditioning field, but a new review shows limited research to fully support this approach. Let’s take a closer look.
The Repetition Continuum—What Does The Evidence Say?
The idea that it is possible to train for strength, hypertrophy, or muscular endurance with specific weight and repetition schemes comes from a 1945 study. Although the basic tenets of this belief may be true, emerging research challenges aspects of this theory and clarifies pitfalls to such a limited view when designing training programs.
Training For Strength
Load is thought to be the dominant factor in increasing strength as heavier load training is generally observed to elicit greater increases in strength independent of training volume. For example, training loads of 80 percent to failure lead to greater increase in neuromuscular strength over 6 weeks than loads of 30 percent. And a meta-analysis shows significant advantages of using heavier loads over 60 percent of the 1RM compared to lighter loads for increasing strength. The trend holds true for younger and older populations and for upper and lower body training.
Heavy Loading Trains The Brain To Exert Maximal Effort
Of course, anyone who has ever lifted heavy knows there’s a substantial difference between maximal load training and loads in the 80 percent range. Maximal loads that are 95 to 100 percent of the 1RM are extremely challenging from both a physical and psychological standpoint. By repeatedly lifting extremely heavy loads, lifters may develop the mental ability to go all out.
Targeting High-Threshold Muscle Fibers
Another issue is whether it’s possible to target the highest threshold muscle motor units without near maximal training. Some studies show that by training to failure you can recruit a substantial percentage of high threshold units, though it’s unclear if recruitment across loading conditions (30 percent v 80 percent) is equal.
Highly trained individuals are likely to experience continued maximum strength improvements when training closer to the 1 RM as one approaches their genetic ceiling. Additionally, studies that follow a periodized program that include strength, hypertrophy, and power focused training produces greater recruitment of muscle fibers than those that use only one loading scheme. As more research comes out, it’s a good bet we will find that including multiple loading protocols that include near maximal load training will yield the greatest gains in strength and hypertrophy.
Training For Hypertrophy
Hypertrophy refers to the growth of muscle tissue. It’s the main concern of body builders and has relevance for all populations because muscle is a key factor in athleticism and plays a vital role in longevity and health, especially in older adults.
It’s generally viewed that hypertrophy is optimized by training in the mid-range of the continuum with 8 to 12 reps and 60 to 80 percent of the 1RM. However, the research is not so cut and dried. Although bodybuilders tend to train in this range, and studies show this type of training generally shows greater post-exercise elevations in anabolic hormones like testosterone, the effect of these transient increases on muscular adaptations is dubious. In regards to the impact of loads on muscle protein synthesis, there is conflicting evidence:
Moderate Vs Light loads For Hypertrophy
Some studies show similar levels of protein synthesis in response to both low (30 percent of the 1 RM) and high (80 percent of the 1RM) loading when training is performed to failure. However, in real life, practicality is important. There’s a case to be made that few people will consistently perform low-load training with the degree of effort that is needed to produce results.
If you’ve never tried low-load training to failure, it’s tough both physically and mentally. Studies show training with low-loads produces more discomfort, displeasure, and a higher rating of perceived exertion than training with moderate-to-high loads. Moderate load training is thought to be more enjoyable, which would promote long-term adherence and encourage better overall outcomes.
Heavy Vs Moderate Loads For Hypertrophy
With regards to the effect of moderate versus heavy loads on hypertrophy, the research suggests they are comparable. This goes against the gospel of the “repetition continuum” with one study finding that trained men who performed the squat and bench press 3 times per week at a loading range of either 8 to 12 repetitions or 2 to 6 repetitions found similar changes in muscle thickness in both the chest and thigh muscles.
Another study showed similar muscle growth in response to 7 sets of 3RM or 3 sets of 10 RM for 8 weeks in trained men. The one downside to the heavy loading condition was overtraining: Participants complained of joint-related overtraining issues observed in response to 8 weeks of 7 sets of 3 RM training.
Once again we see a similar problem to drawing conclusions as with the Strength section: Looking at results over a fixed period of time in which only one training protocol is used will never yield the robust results of a long-term periodized program that allows you to train in phases, building muscle during a hypertrophy-phase and then stimulating those new muscle fibers with a strength phase.
Training For Muscular Endurance
Muscular endurance is the ability to resist muscular fatigue when using submaximal resistance. The theory goes that repeated muscle actions improve buffering and oxidative capacity, an increase in capillarization and mitochondrial density, and enhanced metabolic enzyme activity.
Although there is some evidence of a load-related effect on muscular endurance, other studies don’t support it. For example, one study that compared high (3 sets of 5 to 8 RM), medium (2 sets of 15 to 20 RM), or low (1 set of 30 to 40 RM) loads showed that the medium-load condition produced the greatest increase in muscular endurance in the upper body, followed by the high- and then low-load condition. For the lower body, low-load training produced the greatest increase in muscular endurance followed by similar improvements in the medium- and high-load conditions. Researchers conclude that lighter loads may be more effective for muscular endurance when training the lower body or when testing on an absolute basis (when lifting a fixed load a set number of times such as the NFL bench test whereby the athletes lift 225 pounds as many times as possible).
Much more research is needed on the impact of loading on training adaptations. Studies done on women are particularly important because there is evidence women have greater endurance and capacity to resist fatigue, so there may be significant sex-specific differences in adaptations across the repetition continuum.
Looking at the effect of load without also considering the impact of other training variables such as tempo or rest is a nearsighted approach. When programming workouts, always carefully consider all the training variables in your toolbox to get the best results.
Studies lasting 6 to 8 weeks don’t replicate real-life. A well-designed training program will follow a periodized model with planned phases that allow for progressive overload to ensure the body keeps adapting. In our Foundations of Periodization and Program Design Online Course, we teach how to design short and long-term programs to optimize performance and training outcomes. We also distinguish between functional and general hypertrophy and teach you how to load for each in order to meet unique goals of athletes versus the general population.