What your athletic age is measuring

The short version

Athletic age is your real age adjusted by how much fast-twitch function you have let go of. If you are 42 and everything explosive in your life quietly stopped a few years back, the test hands you a number higher than 42. The gap is the point.

It is a self-assessment, not a lab measurement. It reads six things you already know about yourself and scores them against how fast-twitch decline usually shows up. It is closer to a well-built questionnaire than to a VO2 max test, and we would rather say that plainly than dress it up.

The reason a questionnaire can say anything useful at all is that the underlying decline is steep and well described. A 2012 review in Frontiers in Physiology reports strength being lost two to five times faster than muscle mass with age, and power faster still. Function drops long before size does, which is exactly why asking what you can still do tells you more than a mirror does.

Which six signals does it read?

1. 01

   When you last sprinted flat out

   The single most telling question on the test. Almost nobody sprints by accident after 30, so the answer is a clean read on whether anything in your life still asks for top-end force.

2. 02

   How many days a week you actually train

   Not what you intend to do. What happened last month. Frequency is what separates a body that is maintaining from one that is drifting.

3. 03

   What that training looks like

   Explosive, steady lifting, mostly cardio, or not much. Two men can train the same number of days and be pointed at completely different fiber types.

4. 04

   Two stairs at a time

   A power test disguised as a normal question. Taking stairs two at a time is a small jump, and it is usually the first everyday thing that quietly stops being automatic.

5. 05

   What has crept in

   Softer in the middle, slower, less explosive, or all three. Self-reported, but people are more honest about this than they are about their training.

6. 06

   Your age

   The anchor, not a score. It is what the other five answers get measured against, so the same answers mean different things at 32 and at 53.

What do the three results mean?

1. 01

   Holding the line

   Under about four years of drift. Something in your week is still asking for force, whether you planned it that way or not. This is the easiest position to build from and the easiest one to lose by accident.

2. 02

   Slipping

   Roughly four to seven years ahead of the calendar. The decline has started and it is early. This is where most men who still consider themselves in shape actually land.

3. 03

   Behind

   Eight years or more. Worth reading as good news rather than bad: a large gap is mostly disuse, and disuse is the one input on the list that answers quickly to training.

What is the dormancy figure?

The result also gives you a fast-twitch dormancy percentage. That number is a plain-language restatement of the same score, scaled so an abstract result reads as something concrete.

It is not a biopsy and it is not a measurement of your actual fiber composition. Nobody can tell you that from six questions, and any tool that claims otherwise is making it up. It moves when your answers move, which is the honest thing for it to do.

What does it not measure?

It does not know your bodyweight, your bloodwork, your training age or whether you are carrying an injury. It has no idea how strong you are.

Two men can arrive at the same athletic age from opposite directions: one strong and heavy who has not run in a decade, one lean and fit who only ever does steady cardio. Both are missing the same fiber. That is the thing the test is built to catch, and it is the only thing it is built to catch.

What should you do with the number?

Whatever gap it gives you, the useful question is not how bad it is. It is which of the six answers you could change inside a month.

Usually it is the first one. Sprint properly a few times and the sprint question answers differently, the power question follows, and the number moves. That is not a trick in the scoring. The questions are proxies for a capacity, and the capacity is what changed.

Questions on this

Where the numbers come from

• Mitchell et al., Frontiers in Physiology, 2012

  A quantitative review of age-related decline in muscle size and strength. It reports strength lost two to five times faster than muscle mass, and power faster than strength. The five-year strength figures quoted on these pages come from a 1,678-person cohort study (Hughes et al., 2002) that this review summarizes, not from the review's own measurements.

• Experimental Gerontology, 2013 (PMID 23425621)

  Muscle biopsies from 25 healthy young men, average age 23, and 26 healthy older men, average age 71. Type II fibers were 29% smaller in the older group; the difference in type I fibers was not statistically significant. The same older men then trained for six months, after which their type II fiber size had increased by 24%.

Read next

• The fiber you stopped asking for

  What type-II muscle fiber is, why it fades before anything else, and the training that actually asks for it. Written plainly, with no hacks and no supplements.

• Is it too late at 40?

  What actually declines with age, how fast, how much of it is reversible, and what genuinely changes about training after 40.

• Sprinting after 30, and why it changes how you look

  Does sprinting build muscle? What sprinting does that cardio does not, and how to start again when you have not run flat out in years.