Does Mixing Loading Ranges Lead to More Muscle Growth?
Only have a second? Check out the takeaway below. Have 5 minutes? Check out the rest of the newsletter.
TRAINING TAKEAWAY: While there are limitations to the available data, some evidence suggests that combining low-load and high-load training may maximize muscle growth compared to only training with moderate to high loads. Further, there is likely little downside to this approach. Performing a top set followed by progressively lower load backoff sets is an easy and enjoyable programming strategy to leverage this concept.
Background
So long as sets are sufficiently close to failure, muscle growth seems to occur independent of load (% of 1RM). Indeed, multiple studies have shown essentially identical muscle growth on both the whole muscle and fiber level when training with high or low loads. However, many studies in this area examine the topic in a binary fashion as all sets for each group are performed with only one load. When loading ranges are combined, synergistic effects - greater muscle growth than what would occur with the same number of sets but only in one loading range - may occur. This article will examine the evidence relevant to this question.
Research Review
Researchers have long speculated that high and low loads utilize different mechanisms to deliver a hypertrophic stimulus. For example, some claim that low loads preferentially grow the slower twitch type I muscle fibers due to less motor unit recruitment at any given point in a set. In other words, lower load sets may lead to more time where the type I fibers must predominantly shoulder the loading demands because fewer motor units are recruited at any point in time.
Despite many logically derived theoretical mechanisms, the experimental evidence doesn't seem to support the idea that high and low loads result in substantially different outcomes. Recent meta-analyses from Lopez et al. and Refalo et al. failed to demonstrate significant differences in whole-muscle or fiber-level hypertrophy outcomes when comparing groups training with different loads. However, as mentioned, these analyses compare training conditions with only one load (i.e., high or low).
I'm aware of eight studies (1,2,3,4,5,6,7,8) that compare what I will call "mixed modal" approaches. In these studies, one group trains with only moderate to high loads while the other group trains with a combination of low and high loads. You can see a pooling of their effects on muscle growth below:
Results
Note: The study by Goto et al. did not provide the raw standard deviation to calculate the effect size. The SD from the study from Aguiar et al. was used as it has a similar design.
The pooling of these effects leans in favor of mixed modal approaches [Standardized Mean Difference = -0.19 (95%; Confidence Interval: -0.54, 0.16)], but there are a few things to keep in mind.
First, half (3) of these studies use low loads combined with blood flow restriction (BFR). When pooled as a BFR subgroup, there was a negligible difference between mixed modal and unimodal approaches [SMD = 0.03 (95% CI: -0.42, 0.47)]. However, since BFR decreases the number of repetitions one can perform, it effectively "increases” the load used. For example, performing a set to failure with 30% of (non-blood flow restricted) 1RM without BFR, one may get 34 repetitions. With BFR, they won't be able to reach 34 repetitions, and the degree to which performance drops is likely influenced further by the occlusion pressure. Overall, the lack of observed differences in this BFR subgroup analysis is challenging to explain. On the one hand, the potential effects of mixed modal training may be isolated to very low loads (perhaps <40% of 1RM), and BFR may effectively "increase” the load out of that range in many cases. On the other hand, BFR augments the metabolically stressful environment created by any load, and this is the primary suspected mechanism by which low-load training would produce differential effects compared to high-load training.
In the other subgroup of studies - simply non-BFR studies - a second consideration exists. The non-BFR studies show a potentially practically relevant effect in favor of mixed model approaches [SMD= -0.36 (95% CI: -0.85, 0.13)], but 2 out of 5 perform additional sets in the mixed modal group compared to the unimodal groups. This is notable because additional sets are generally an advantage for muscle growth. However, in the study by Aguiar et al., the light load sets were performed with 20% of 1RM. In other research by Lasevicius et al., a group training with only 20% of 1RM did not experience optimal hypertrophy. Thus, this suggests that synergistic effects of low-load training may exist when combined with high-load training. That said, the overall effect is essentially zero when this study is removed [SMD= -0.05 (95% CI: -0.30, 0.19)], so caution is warranted.
Practical Applications
Based on the above findings, I believe there is intriguing evidence that warrants experimenting with the inclusion of both high and low load training when aiming to maximize muscle growth. While the evidence is limited, the potential downsides are minimal. At worst, low load training will be just as effective as high load training on a per set basis. At best, a mixed modal approach will provide a synergistic effect and result in greater total muscle growth.
An intuitive way to apply this concept is with backoff sets. Traditionally, backoff sets are used in strength sports to accumulate additional volume that would be otherwise inefficient with very heavy loads. For hypertrophy, performing an initial heavier set (e.g., 5-10 reps) followed by progressively lighter sets (e.g., 10-15 reps followed by 15-20 reps) would allow for the theoretical advantages of mixed modal loading strategies with minimal downside.
Similar strategies have been shown to be effective in the research, such as drop sets. As we’ve discussed in a previous newsletter, drop sets seem to result in comparable muscle growth to straight sets. However, drop sets feature short rest periods and seem to decrease the efficiency of muscle growth on a per set basis. With increased rest periods between backoff sets, mixed modal strategies could feasibly surpass the muscle growth of straight sets at a fixed load.