Redefining Progress in Strength Training

For what it’s worth, I write all my articles without the use of generative AI. – Nate

“Essentially, all models are wrong, but some are useful.”

George E. P. Box

I’ve spent over 200 hours testing IronOS in my own training, using it with clients, and prompting AI to write code and iterate on every pixel in the app.

Throughout building and testing, I kept coming back to one thought: “Charting progress is fun when the data trends up, but what happens when age or other circumstances make progress a thing of the past?”

Enter the Durability Score. It aims to accomplish two things:

1. Give a novice lifter a general strength target they could hit in 1-2 years of training, scaled to their sex, weight, and age.
2. Redefine “progress” for the lifter approaching 50 so it’s graded on strength retained rather than PRs achieved.

While solving for number one, I learned that strength standards simply don’t exist. I’ve got the full methodology for the Durability Score at this link, but to keep things short: all strength standards are arbitrary.

The best I could do was work with AI to pick conservative numbers from sanctioned/drug tested powerlifting meets to serve as benchmarks for the most people, through most ages.

Solving for number two was simpler, since we have a clearer idea of how much strength a highly motivated lifter loses year over year.

In short, the Durability Score does two things. First, it provides a strength standard for the novice lifter to strive for. A score of 100 means they’re meeting the standard. Once the benchmark is met or exceeded, the lifter’s own PRs become the standard going forward.

Second, it redefines “progress” as the amount of strength a lifter retains year over year. Since the standard decreases yearly to account for age-related decline, a lifter can maintain a score of 100 as long as they hold on to their strength in line with expected declines.

Like every other model, the Durability Score is “wrong,” but it’s also really useful.

My own training data tells the story of how the Durability Score can be used in practice. I started barbell training in late 2020 with the aim of building and retaining as much strength as possible heading into my second liver transplant. Not the best circumstances for maximizing training gains, but life tends to work that way.

I didn’t have the Durability Score as a metric leading up to my second transplant, but its logic was constantly running in my mind: life is going to get harder, and I need as much strength and muscle as possible to reduce my suffering and improve the odds of a great transplant outcome.

In the data, you can see a rapid rise in my Durability Score as I began barbell training in 2020. It rose steadily until it dropped precipitously in early 2025 during recovery from my second transplant.

To say my training was a success would be an understatement. In less than a year post-transplant, I’ve already exceeded all my pre-transplant strength peaks.

There’s nothing impressive about my absolute numbers, but the story inside them shows how the body can adapt under extremely challenging circumstances (liver failure), recover from transplantation, and then set new strength benchmarks.

My hope is that the Durability Score can serve as a similar motivator for you. To narrow your focus on one of the variables that matters most as we age, building muscle, preserving strength, and preparing your body for the demands of getting older.

If you have any questions about the Durability Score, suggestions for improving it, or have found it helpful in your training, I’d love to hear what you’ve learned.