Note: This article was the MASS Research Review cover story for April 2024 and is a review of a recent study by Chaves et al. If you want more content like this, subscribe to MASS.
Key Points
Women and men did unilateral leg extensions 2-3 times per week for 10 weeks. The subjects increased the load lifted as needed on one leg and increased the number of reps per set on the other leg.
The researchers found that both methods of progressive overload led to significant increases in leg extension 1RM and vastus lateralis cross-sectional area. There were no significant differences in the pre- to post-study changes between conditions.
Various progressive overload strategies can maximize short-term gains in novice trainees. In more trained individuals, especially those aiming to maximize strength, load progression is essential. Additionally, choosing between increasing load or reps is not a binary choice; these progressive overload strategies can be used in conjunction with each other.
Every week for years, I stared at my training spreadsheet, agonizing over how to achieve progressive overload. Should I increase the load? Should I increase the reps? Should I add sets? Should I shorten the length of the rest period? Should I lift the same weight but do so with my hat backward to ensure I set a new personal record? Sometimes I would agonize so much over these details that I’d try to implement all of them into one training block, which was a surefire way to overcomplicate things (pro tip: even if it’s not “optimal,” pick a strategy, believe in it, and stick with it for at least a little bit). Despite my previous indecision, these are all equally legitimate strategies to achieve progressive overload or to set a PR (well, maybe not the hat adjustment). But is one better than the other?
A previous between-subjects study by Plotkin et al (2 – MASS Review) found that trained women and men had improved strength and muscle size to a (mostly) similar extent when comparing load and rep progression. However, strength gains may have been slightly greater (+5.9%) with load progression in comparison to rep progression. That study recruited trained individuals but tested strength on a Smith machine, despite the fact that participants were more accustomed to the free-weight squat. Thus, these results cannot be perfectly extrapolated to other populations or to “specific strength” (testing strength on the trained exercise). Furthermore, one study is hardly going to deter individuals from agonizing over how to best progress training to maximize muscle growth. Fortunately, a new within-subjects design study by Chaves et al (1) once again compared load and rep progressions for strength and hypertrophy in a mixed-sex population, but this time they tested specific strength.
Purpose and Hypotheses
Purpose
The primary purpose of the reviewed study was to compare changes in leg extension 1RM and vastus lateralis cross-sectional area over 10 weeks of training that progressed either the load lifted or reps performed in untrained men and women.
Hypotheses
The researchers hypothesized that load progression would lead to greater increases in both strength and muscle size than volume progression. They anticipated that load progression would lead to greater changes in the volume load (sets × reps × load lifted) over time, which would ultimately translate to greater gains in strength and size.
Subjects and Methods
Subjects
Thirty-nine women (n = 19) and men (n = 20) who had not performed resistance or aerobic training for at least six months participated in the study. Additional characteristics of the subjects are presented in Table 1.
Study Overview and Training Protocols
The researchers used a longitudinal within-subjects design in which all subjects completed each training condition. Specifically, over the course of 10 weeks, all subjects performed unilateral leg extension training and achieved progressive overload on one leg by increasing the load while they increased the reps throughout the study on the other leg. Subjects trained both legs two to three times per week for a total of 23 training sessions. The condition-specific protocols and progression schemes are presented in Table 2.
Outcomes
Researchers assessed vastus lateralis cross-sectional area via ultrasonography and leg extension 1RM before and after the 10-week training intervention. Researchers also compared the load lifted (absolute and % of 1RM), number of reps performed, and volume load between the conditions.
Findings
Overall Findings
The researchers found that the subjects significantly increased both strength and cross-sectional area (p < 0.0001). There was no significant condition × time interaction for changes in either strength (p = 0.20) or cross-sectional area (p > 0.87; Table 3). Furthermore, there was no significant difference in volume load progression between the training conditions (p = 0.19; Figure 1).
The only significant differences that existed were directly related to study design choices. Specifically, the subjects lifted heavier loads in the load progression condition (p < 0.001; Table 4) and performed 292 more reps in the rep progression protocol (1292 ± 302 versus 1000 ± 67 reps; p < 0.001).
Interpretation
The presently reviewed study from Chaves et al (1) found that achieving progressive overload by increasing load or increasing reps led to similar gains in leg extension 1RM and quad hypertrophy. Another recent study by Plotkin et al (2 – MASS Review) also compared load and rep progression and found similar results. This interpretation compares these two studies and discusses the situations in which the specific method of progressive overload may matter.
Comparison of Chaves et al (1) and Plotkin et al (2)
On the surface, the protocols in both studies and the findings from both studies (1, 2) were similar, but important differences existed. Regarding the similarities, Plotkin et al (2) used a nearly identical protocol that consisted of a load progression group starting with 4 × 8-12RM (9-12 RM was used in the present study), and the load was increased when failure was reached outside of the target rep range. Plotkin et al had the rep progression group complete 4 sets to failure with a 10RM each session and increased reps as they could, which was identical to the present study. Furthermore, both studies reported that group-level gains in strength and muscle tended to be similar between progression protocols. However, Plotkin et al reported that strength increased “slightly” more (+5.9%) in the load progression group, and that the rep progression group experienced a 1.8% greater change in the sum of all rectus femoris site muscle thicknesses. Therefore, it is imperative to discuss methodological differences to determine why there may have been slightly different findings and what this means for the lifter. The three methodological differences to discuss are: 1) training status of the subjects, 2) exercise selection, and 3) the study design.
The first thing to consider is whether the percentage differences in favor of load (strength) and rep (hypertrophy) progression in Plotkin et al (2) are real differences. I think there is merit to say that individuals generally gained more strength from load progression in Plotkin et al’s study, but probably not enough merit to say that rep progression was superior for hypertrophy. In the presently reviewed study from Chaves et al (1), there was essentially no difference at the group level (+1.4% in favor of load progression) for leg extension 1RM when progressing load. Although load is clearly the primary driver of strength gains (3), the subjects in the current study were either untrained or had not trained for at least six months, whereas those in Plotkin et al had trained for nearly four years, on average. Although load may play a role in strength gain for untrained participants, it seems to matter more for trained individuals (3). Furthermore, Glass et al (4 – MASS Review) observed robust strength gains in untrained individuals who used only ~40-60% of 1RM. Therefore, it’s possible that the novice training status of subjects in the presently reviewed study explains the lack of between-condition differences in strength gains.
Chaves et al (1) had participants train a low-skilled movement, the leg extension, while Plotkin et al (2) utilized the free-weight back squat for training sessions. It’s possible that the subjects in Plotkin et al experienced enhanced strength benefits due utilizing a highly skilled free-weight exercise. Interestingly, Plotkin et al actually tested strength on the Smith machine squat despite training with a free-weight squat; however, it is possible that the Smith machine squat was similar enough to the free-weight squat so that heavier loading in training for the load progression group was more beneficial. I am a bit torn on whether or not I really think training the free-weight squat with heavier loading was more beneficial for Smith machine strength, so I would probably lean more into the training status argument to explain the potentially greater strength gains in Plotkin et al.
Lastly, the Plotkin et al (2) study had a between-subjects design, while the present study by Chaves et al (1) had a within-subjects design. I have previously written about the differences between these two study designs in greater depth. In brief, a between-subjects study, such as Plotkin et al, compares two groups of subjects, in which one group performs one training program and the other group performs a different training program. Importantly, the individual response to training is highly variable (5), and this design does not allow the researcher to determine how an individual would respond to the other protocol. Therefore, in an underpowered study (which is many, if not most, training studies), if one group had significantly greater gains than another group, on average, it is possible that many in one group did not respond well to that protocol rather than the protocol itself being inferior for everyone. For example, in the study by Plotkin et al, the range of increase in Smith squat 1RM was +5.8-55.7 kg (load progression group) and +4.0-33.2 (rep progression group); thus, we do not know if some individuals would have responded better or worse in the opposite protocol. In contrast, Chaves et al (1) used a within-subjects design. Unfortunately, Chaves et al did not report individual subject data; therefore, we still do not know how individuals responded to each protocol. However, the differences between groups for strength gains (1.2%) and muscle growth (0.6%) were very small; thus, it would be surprising if there were large differences in within-individual rates of progress.
It should also be noted that while a within-subjects design does allow us to examine how an individual responds to both protocols, there is an important limitation of this design as it pertains to strength gains. Specifically, training one limb will lead to the “cross-education” effect, which is the improvement in strength of the opposite limb that is trained (6). While I wrote about this in depth here, data show that if individuals train one limb and not the other they will increase strength about 7-10% in the untrained limb, on average, in 4-12 weeks when training with ≥60% of 1RM (7, 8). Therefore, it’s possible in the presently reviewed study that the benefits of increased loading in the load progression group were also realized in the rep progression group, which explains the lack of between-condition difference in strength gains. To be clear, I don’t think that’s why the strength gains were so close (1.2% difference) between groups, but it’s possible that the cross-education effect dampened the difference, even if to a trivial degree. Importantly, training one limb will not increase muscle size in the other limb; thus, the cross-education effect does not manifest for hypertrophy.
In reality, the findings of the two studies were quite similar. It’s worth reiterating that Plotkin et al (2) did not find that there were true differences between groups for strength gains, rather the point estimate for strength gains “slightly” favored the load progression. Furthermore, similar hypertrophy between groups is not surprising, as the current study found that volume load and volume load progression were not significantly different between groups, and both studies were set-equated between the load and rep progression protocols.
Specific Situations Dictating Progressive Overload Style
When I reviewed the aforementioned study by Plotkin et al (2) in Volume 6, Issue 12, I discussed many different ways to achieve progressive overload, and how these different strategies could be intertwined. There is not much sense in a comprehensive rehashing of those details, since you can simply click here and read that article. In brief, the load could be progressed based on a predetermined percentage or absolute loading change, a previous session RIR or velocity, or by plus set performance to name a few. Additionally, the load, rep, and set progressions are not mutually exclusive and can be intertwined. For example, this table demonstrates how the load is only increased after a lifter can perform a certain number of sets with a given load, illustrating how the load is only increased after a certain number of reps are achieved with that given load. Now that we are aware of all these progressive overload strategies, let’s discuss when different strategies might be preferable.
Let us begin with progression when strength is the primary goal. Obviously, load progression is an essential and non-negotiable type of progression that must occur to maximize 1RM strength over the long turn. However, does load progression need to happen all the time? The answer is a clear “no.” For example, a powerlifter can use a simple model in which they increase the load by 2.5 kg each week as they approach competition, ultimately reaching heavy loads (i.e., ≥90% of 1RM); however, they may not be able to progress load each week, in which case they should not force it. In these situations, it may be better to add an additional set or rep and then increase the load the following week. Alternatively, the lifter could autoregulate the training load from week-to-week when peaking for a powerlifting meet or gym test day; thus, they would only increase the load when they were able to. For example, a lifter could program 3 × 2 @1-2 RIR and would lift whatever load they could do for two reps in that RIR range, which would sometimes be heavier, lighter, or even the same compared to the previous week’s training.
Moreover, someone with strength as their main goal will still perform volume blocks from time to time, in which muscle growth is targeted. In these situations, there is no pressure to increase the load, at least not each week. Therefore, intertwining load with rep or set benchmarks is an effective strategy. As seen here, a lifter could be prescribed a set and RIR benchmark in which the load only progressed once the benchmark was reached. For example, a lifter could be prescribed squats with 3 × 8 with 100kg and add a set each week as long as they complete all sets at ≥2 RIR. Then, once they were able to perform 5 × 8 at 2 RIR they would increase the load. Alternatively, a strength-focused individual in a volume block could tie load increases to a rep benchmark. In volume blocks, individuals focused on strength may utilize programming strategies, such as rest-pause training, which have progressive overload built-in by attempting to perform more reps each time the strategy is used.
I’ve been on record saying that training for muscle growth is a lot more forgiving than training for strength. Of course, the two (hypertrophy and strength) are interrelated, but if strength is the main objective, then load progression is a must at some point, periodization seems to matter (9 – MASS Review), and a lifter must practice the specific exercise with which they are going to test their strength (i.e., a powerlifter must perform the squat, bench press, and deadlift). While there are some “rules” for hypertrophy such as more volume (to a point) drives muscle growth and the individual should have enough exercise variety, traditional (strength focused) models of periodization do not seem to matter (9) and progressive overload can be achieved through various methods. An individual can use rep or set progression models as described above. The lifter can also manipulate RIR throughout the course of a training block to achieve progressive overload. Specifically, a lifter could keep the number of sets constant and increase the load so that the RIR decreases from week-to-week to train closer to failure. Alternatively, a lifter could choose to maintain the same load and add sets each week during the training block. In this situation, the RIR might actually increase, but the increase in RIR (training farther from failure) might make it more feasible for the lifter to add multiple additional sets. Yet another strategy could be for the lifter to shorten interest rest periods to make each set more difficult. This time-saving strategy may also allow the lifter to add an extra set. To be clear, I am not saying that any one strategy is any more desirable than another; rather, I am just presenting various options. Table 5 summarizes the appropriate progressive overload strategies for both strength and hypertrophy.
Coach’s Corner
Let’s finish up with a “coach’s corner” section to discuss practical points for coaches and lifters when putting progressive overload into action.
First, lifters will not be able to progress every session or week, and anyone who has trained for a substantial amount of time knows this. Therefore, since you know this, do not force progression every week and try your best (although I know it’s tough) not to get frustrated if you are lifting the same load for a couple of weeks in a row. Recall that the goal is progressing over time. The goal is not to increase the load (or set or reps) for its own sake. Saying “I did 40 sets of quads this week” shouldn’t be a badge of honor (although it is kind of awesome). If that’s fun, by all means, go for it. However, if the goal is to maximize strength or strive for the best aesthetics then don’t chase the set, rep, or load number, chase the strength or physique progress, which may sometimes come from being disciplined enough to not progress variables during a single week.
Secondly, don’t get paralyzed while deciding which progressive overload strategy to use. All of the strategies mentioned in this article have merits. Find one that applies to your goals and stick with it for an entire training block. As a coach and lifter, I have agonized many times over what exact method to use for myself or for various athletes. Typically, I am better at choosing a method for others, but for myself, I would often try to integrate too many different concepts, mitigating their effectiveness or losing focus on the main goal (progress). My caution is to avoid this trap and find a logical progressive overload strategy that is appropriate for you (or your client’s) goals and stick with it for a decent period of time.
Next Steps
In my review of Plotkin et al (2), I called for a new study comparing load versus rep progression, but with a free-weight exercise used in both training and testing. The presently reviewed study was a good addition to the literature for the hypertrophy outcomes because it was a within-subjects design. For strength outcomes, it’s possible that the cross-education effect confounded the results, although I doubt to a very meaningful degree. Additionally, in a within-subjects design movements such as squats and bench presses cannot be used. Therefore, I will again suggest that the next step would be to compare load versus rep progressions in trained individuals using a free-weight squat or bench press as both training and testing exercises.
Application and Takeaways
Chaves et al (1) found that over 10 weeks, untrained individuals experienced similar strength gains and hypertrophy regardless of whether they achieved progressive overload by increasing the load or the number of reps, although we should be cognizant that the cross-education effect may have confounded the strength findings. However, the lack of differences between training protocols in this study does not mean that the method of progressive overload is always immaterial. In general, those interested in strength must increase their load at times, specifically in the training block immediately preceding a strength competition (e.g., powerlifting meet) or 1RM test day. When muscle growth is the main goal, lifters have much more flexibility to achieve progressive overload via load and/or repetition adjustments. Ultimately, progressive overload strategies can be intertwined and coaches and lifters should not consider themselves bound to the binary choice of load or rep progression.
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This article was the cover story for the April 2024 issue of MASS Research Review. If you’d like to read the full April issue (and dive into the MASS archives), you can subscribe to MASS here.
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References
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