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TRAINING TAKEAWAY: For sets aimed at strength development, adding load week to week is likely superior. For sets aimed at hypertrophy, adding reps may provide practical benefits. Further, there may be cases where manipulating rep range via progression methods can be beneficial for specific muscles.

Introduction

Most are familiar with the concept of progressive overload: once you adapt to a training stimulus, you must add more of something - such as reps or load - to ensure the next training session is stimulative. However, the best choice of this “something” has received little attention in the research.

A new study by Plotkin and colleagues provides the first experimental look at progression methods and their influence on strength and hypertrophy.

Study Design

Thirty eight men and women with an average training age of 3.8 years participated in this study. Subjects were randomly assigned to a Load Progression or a Repetition Progression group. Both groups performed sets of 8-12 to failure in the first session. As the group names suggest, the Load Progression group aimed to increase load at a given rep number whereas the Rep Progression group aimed to increase reps at a given load.

Each session consisted of four sets of each barbell squats, leg extensions, standing calf raises, and seated calf raises to failure. These sessions were performed twice a week; so, the quads were trained with 16 sets per week. The training intervention was 8 weeks.

Hypertrophy was assessed with B-mode ultrasound. For the quadriceps, six total sites were assessed. Three of these (one proximal, one middle, and one distal) were the total thickness of the rectus femoris and vastus intermedius, which I’ll call RF+VI going forward. Check out figure 1 from a different paper for a visual representation of what these images looked like. The other three (again, one proximal, one middle, and one distal) were the total thickness of the vastus lateralis and vastus intermedius, which I’ll call VL+VI. Check out this image for a visual representation of this measurement. A few other measurements of hypertrophy were assessed, including thickness of the lateral gastrocnemius, medial gastrocnemius, and soleus. Finally, 1RM back squat was assessed on a Smith machine.

Results

You’re probably used to hearing research results in a binary fashion - there either was or wasn’t a significant difference between groups. This traditional approach is called null hypothesis testing; after running the analysis, researchers can determine whether there is enough evidence to “reject the null.” To put it simply (and lose some nuance), the data do or do not provide sufficient justification that there is a difference between groups.

These researchers took a different approach and instead reported estimated differences between groups and a confidence interval around that estimate. For example, the between groups squat 1RM gains point estimate was 2.0 kg in favor of the Load Progression group. In other words, these data indicate that the Load Progression approach increases squat 1RM an additional 2.0 kg over the Rep Progression approach. However, the 90% confidence interval ranged from 7.8 kg greater gains in the Load Progression group to 2.4 kg greater gains in the Rep Progression group. Put simply, 1RM strength leaned slightly in favor of the Load Progression approach, but since the between group confidence interval crossed zero, this could be due to sampling variance.

When pooling the proximal, middle, and distal hypertrophy measurements of VL+VI, the between groups point estimate was right around 0 mm.

When pooling the proximal, middle, and distal hypertrophy measurements of RF+VI, the between groups point estimate was 2.8 mm in favor of the Rep Progression group (90% confidence interval ranging from -0.5 to 5.8).

In short, these results indicate that progressing reps (at a constant load) and progressing load (at a constant rep number) are both effective strategies for hypertrophy and strength development. However, the strength gains leaned in favor of the Load Progression group and the RF+VI hypertrophy leaned in favor of the Rep Progression group. Let’s take a closer look at each of these.

Discussion: Strength

The between groups point estimate of only 2.0 kg better strength gains in the Load Progression group may have surprised some as the Load Progression group used heavier loads throughout the study. Specifically, the Load Progression group trained with an average of 83.7% of their post-testing 1RM in their final training session. This is compared to 62.0% for the Rep Progression group.

Given this considerable difference in load, I think the lack of an overwhelming difference is an artifact of the population and study design. The average pre-testing squat 1RM was ~80 kg, and the authors noted that not all subjects were regularly performing squats prior to the study. Since the relationship between load (% of 1RM) and strength gains is likely weaker with less-trained populations, this may explain the lack of difference in strength gains between groups. Perhaps more importantly, the 1RM testing and the training were performed on different equipment - 1RM testing was performed on Smith machine squats whereas the training was performed on barbell squats. If the subjects were better trained and the strength testing was performed on barbell squats, I suspect the strength gains would strongly favor the Load Progression group.

Practically, if the goal of a set is to develop strength skill, a load progression strategy is likely going to lead to the best strength gains (or at least not be any worse than a rep progression strategy). To program with a load progression strategy, you can simply have a constant repetition and RPE target each week, such as 3 reps at an 8 RPE. As the lifter gets stronger, load is added to achieve 3 reps at the RPE target. This approach can also be paired with what we like to call “artificial progression,” which decreases reps or increases RPE week-to-week. So, if last week was 3 reps at 8 RPE, the next week may be 2 reps at an 8 RPE or 3 reps at a 9 RPE. Since week-to-week strength gains are often unrealistic for advanced lifters, sticking with the same rep number and RPE each week can lead to repeating a load for many weeks. On the other hand, this “artificial progression” allows lifters to add load most weeks. This seems to lead to greater lifter engagement, more momentum in training, and ultimately better facilitation of “true” progress.

Discussion: Hypertrophy

Since the researchers examined six total quadriceps sites - three anterior sites (RF+VI) and three more laterally (VL+VI) - we have more to work with in this study than most. However, more measurements also increases the likelihood of a spurious finding. I mention this because it’s certainly possible that the point estimate of 2.8 mm greater growth of the RF+VI in the Rep Progression group could be a whole lot of nothing. Caution aside, let’s look closer at why progression strategies may influence hypertrophy.

In this study, any differences in outcomes are likely the result of differing rep ranges. Using the leg extension as an example, the Load Progression group stayed at sets of ~10 reps throughout the entire study whereas the Rep Progression group started at sets of ~10 reps but finished with sets consisting of an average of 14.7 reps. So, the greater RF+VI hypertrophy could be a result of a higher rep range. Some may push back and cite the well-established finding that a wide range of reps can lead to similar hypertrophy. However, there may be some edge-case scenarios where it does matter, and it may be that differences can only be detected with a more comprehensive look at muscle growth by measuring multiple sites.

For example, with lighter loads, squats are generally more quad-dominant and thus the hip extension demands are lower. Since the Rectus Femoris is a hip flexor in addition to a knee extensor, its activity opposes hip extension. So, it makes sense for the Rectus Femoris to contribute less with heavier loads as the hip extension demands increase. With the lighter loads that the Rep Progression group used, the Rectus Femoris may have contributed to a more quad-dominant squat and thus received a greater hypertrophic stimulus. Now, the takeaway here isn’t to go do sets of 30 on squats in the name of Rectus Femoris growth (that’s likely an inefficient way to train them anyway). However, I wanted to provide this as an example of how progression methods (and thus rep ranges) may influence relative contribution of the involved muscles.

This section was largely hypothetical and I hopefully made it clear that the slightly better growth at the RF+VI sites for the Rep Progression group should not be over-applied. However, for practical reasons, I do think that Rep Progression is generally superior for protocols aimed at hypertrophy. If training in a rep range conducive for hypertrophy (~6-25 reps), it’s difficult to know exactly how much load to add if you’re using a strict rep number. Instead, it’s often more precise to simply stop the set at the desired RPE. If more reps are completed than last session, then rep progression has occurred.

Eventually, rep progression will lead to very high rep ranges, necessitating more load. This leads me to an important point: rep progression and load progression are not mutually exclusive. Instead, a rep range can be used; once you’re hanging out at the top of that rep range with a given load, you can add load for the next session. This is often referred to as “double progression.”

Conclusion

Overall, load progression is likely a good default strategy for strength development. For hypertrophy, rep progression or a combined approach may provide practical benefits. Further, there may be cases where manipulating rep range via progression methods can be beneficial for specific muscles.

Importantly, these protocols are not mutually exclusive within a session or even within an exercise. For example, you may use a load progression protocol for a top set of squats, then perform backoff sets on squats with a double progression approach, and finish with a true rep progression protocol on leg extensions.