Modeling strength gains over time

Predicting and projecting strength gains over time has utility for lifters and coaches. A recent study by Steele and colleagues helps us better understand the typical trajectory and time course of strength gains.
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Predicting and projecting strength gains over time has utility for lifters and coaches. For example, if you want to set realistic goals for your next training cycle (or your next year of training), it’s nice to have a number that’s grounded in reality, instead of just picking random targets out of thin air. Similarly, your level of investment in powerlifting might scale with the amount of competitive success you believe you might attain – you might approach training a bit differently if you think you have the potential to compete for a world championship in a few years.

A recent study by Steele and colleagues helps us better understand the typical trajectory and time course of strength gains (1). The researchers had access to data from a private gym company. At these gyms, all clients trained on standardized machines once per week, with sessions overseen by personal trainers. Each training session involved a single set of six different exercises, performed to failure, with training loads increasing over time when trainees comfortably completed more than 6 reps in a set. So, while the training protocol employed at these gyms certainly doesn’t perfectly mirror powerlifting training, this dataset had a few huge advantages. First, it was a huge dataset: it included training data for nearly 15,000 trainees. Second, the trainees all followed a standardized training protocol. Third, many people in this dataset followed the standardized training protocol for over a year, with some people following the training protocol for nearly seven years. Thus, this dataset is ideally suited for investigating the time course of strength gains over time, with as few confounders as one could reasonably hope for. 

To supplement this dataset, Steele and colleagues also modeled strength gains over time from two other sources. First, they randomly selected 10,000 lifters with competition data in the OpenPowerlifting dataset, to see if strength gains over time in competitive powerlifters followed the same pattern as was observed in the ~15,000 clients from the Dutch gym chain. Second, they surveyed the /r/weightroom subreddit, asking approximately 1,000 lifters their powerlifting total, and how long they’d been training. This provided the researchers with middle-of-the-road data – redditors in /r/weightroom probably aren’t quite as invested in training as competitive powerlifters, on average (though there are certainly competitive powerlifters who post in /r/weightroom), but they’re considerably more invested than the ~15,000 folks in the primary dataset.

In all three of the datasets, strength gains over time followed a linear-log relationship. In other words, if someone puts 10kg on a lift after one month of training, it’ll probably take them about 2 months to add another 10kg after that, about 4 months to add another 10kg after that, about 8 months to add another 10kg after that, etc. You can see this relationship in Figure 1 (clients of the gym chain) and Figure 2 (competitive powerlifters).

Graphic by Kat Whitfield

Graphic by Kat Whitfield

As with any sort of prediction, I wouldn’t advise you to interpret this relationship between time and strength gains literally and fatalistically. For example, maybe you’ve only added 5kg to your total over the past six months, but you’ve also been training inconsistently, you’ve been stressed out of your mind, and you’ve been eating poorly. I certainly wouldn’t propose that it’ll take you a year to add another 5kg to your total, even if your life calms down and your diet and training consistency improve. Similarly, if you didn’t gain much strength over your first year of training, while lackadaisically following a sub-par training program, that doesn’t mean you should logarithmically project your lackluster early rate of progress into the future, and conclude that you’ll never be particularly strong. Conversely, if you recently added 40% to your total after completing the best block of training you’ve ever experienced, you’re certainly not guaranteed to add another 40% to your total over your next two training blocks. In short, most predictions and extrapolations should be cautious predictions and extrapolations – projecting your strength gains over time isn’t an exception to that rule.

With that said, I do think that this study provides us with a decent heuristic: each equally-spaced milestone in your training career will probably take about twice as long to complete as the prior milestone. If it took you three years to improve your squat from 400 pounds to 500 pounds, there’s a pretty decent chance that you’ll eventually be able to squat 600 pounds, but you should approach this goal with the expectation that it’ll take you about six years, unless you have room to significantly improve your approach to training, nutrition, or recovery. Conversely, if going from 400 pounds to 500 pounds only took you six months, aiming to complete a 600 pound squat within the next year might be a motivating but realistic goal.

I want to make two more quick notes before wrapping up. First, I think it’s helpful to think about strength gains this way – gains are logarithmic, meaning progress progressively slows down over time – rather than conceptualizing any sort of “genetic limit.” I fully believe that there are always strength gains to be made, until either injuries or the aging process finally slows things to a halt. Second, I want to draw your attention to one of the sub-analyses in the paper. The researchers compared relative strength gains in males and females over time, finding that the rates of progress were comparable over six years (Figure 3).

Graphic by Kat Whitfield

For years now, I’ve been saying that relative rates of strength gains are comparable in male and female lifters. And for years, I’ve been getting pushback from people claiming that lower levels of endogenous testosterone production mean that female lifters necessarily have a smaller capacity for strength gains. At this point, we have meta-analytic evidence from controlled studies (2), competition data from competitive powerlifters, and now a multi-year study on nearly 15,000 males and females following the same training program (1) – all three of these sources of evidence conclude that male and female lifters make comparable relative strength gains over time. If you’re still unconvinced, I’m honestly not sure what could possibly convince you.

Note: This article was published in partnership with MASS Research Review. Full versions of Research Spotlight breakdowns are originally published in MASS Research Review. Subscribe to MASS to get a monthly publication with breakdowns of recent exercise and nutrition studies.

References

  1. Steele J, Fisher JP, Giessing J, Androulakis-Korakakis P, Wolf M, Kroeske B, Reuters R. Long-Term Time-Course of Strength Adaptation to Minimal Dose Resistance Training Through Retrospective Longitudinal Growth Modeling. Res Q Exerc Sport. 2022 May 19:1-18. doi: 10.1080/02701367.2022.2070592. Epub ahead of print. PMID: 35591809.
  2. Roberts BM, Nuckols G, Krieger JW. Sex Differences in Resistance Training: A Systematic Review and Meta-Analysis. J Strength Cond Res. 2020 May;34(5):1448-1460. doi: 10.1519/JSC.0000000000003521. PMID: 32218059.
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