Guide/After 40
Is it too late at 40?
No. The muscle lost with age is specifically fast-twitch fiber, and it responds to training well beyond 40. In one study, men averaging 71 trained for six months and their type II fiber size increased by 24%, accounting for essentially all of the muscle they gained. Forty is not the closing of a window.
The honest answer is more interesting than the reassuring one, because what declines is narrower and more trainable than most people assume.
What actually declines with age?
Less than the general gloom suggests, and it is specific rather than general.
Muscle mass goes slowly. What goes considerably faster is what that muscle can do. A 2012 quantitative review in Frontiers in Physiology reports strength being lost two to five times faster than muscle mass, and power faster than strength. The cohort study it cites, following 1,678 older adults over five years, found men losing around 16% of their knee extensor strength while losing only 5% of the thigh muscle.
Underneath that is a fiber story. A 2013 study in Experimental Gerontology took biopsies from 25 healthy men averaging 23 and 26 healthy men averaging 71: type II fibers were 29% smaller in the older group, while type I fibers showed no significant difference. You do not lose muscle evenly. You lose the fast kind.
Why do you feel it before you see it?
Because function is falling several times faster than size, so the first evidence is never in the mirror.
It is the second step of a sprint for a closing door. Standing out of a low chair. Two stairs at a time stopping being automatic. Men usually notice they got slow a long time before they notice they got smaller, and then attribute it to age generally rather than to the one specific thing that changed.
This is also why a bodyweight that has not moved in a decade can be genuinely misleading. Same number on the scale, different tissue underneath it.
Is the decline reversible?
Substantially, and the best evidence for that is in the same study as the bad news.
After the biopsy comparison, the older men in that 2013 study, averaging 71, did six months of resistance training. Their type II fiber size increased by 24%, and that growth accounted for essentially all of the increase in their quadriceps muscle size. The fiber that had shrunk the most was also the fiber that came back.
That is men in their seventies. Whatever is happening at 43 is a considerably easier problem, and it has had far less time to accumulate.
What no study will tell you is how much of your own gap is age and how much is the decade you spent not asking anything explosive of your body. In most cases the second number is much larger than the first, and it is the one that responds fastest.
Does training actually get harder after 40?
Some of it does, and pretending otherwise helps nobody.
Recovery is the real change. The same session takes longer to come back from, so training frequency has to be honest rather than aspirational, and consecutive hard days stop being free.
Connective tissue is the other one. Tendon and ligament adapt more slowly than muscle does, which means your legs will feel ready to sprint before the tissue holding them together is. Almost every injury in this kind of training happens in the first few weeks, to someone whose muscles could handle what their tendons could not.
Neither of those is a reason not to train explosively. They are reasons to build up to it over weeks rather than testing it on a Saturday.
What should you do differently after 40?
- 01
Train the fast half on purpose
It is the part that is declining, so it is the part with the most to give back. Left to itself it does not maintain, it fades.
- 02
Earn the intensity over weeks
Hills before flat sprints, submaximal before maximal, a month of build-up before you find out what all-out feels like now.
- 03
Count hard days, not sessions
Two or three genuinely high-force exposures a week, counting heavy lifting and sprinting together. The easy work in between is not the thing to cut.
- 04
Judge it on performance first
Faster, higher, heavier moves before the mirror does. If those are improving, the visible change is downstream and on its way.
What should you not do?
Do not start by copying what a twenty-two-year-old does on the internet, and do not start by copying what you did at twenty-two. The programming is not the problem in either case. The on-ramp is.
Do not treat soreness as the measure. At 43 you can generate soreness trivially and it tells you almost nothing about whether the session did what it was for.
And do not spend another year adding volume to training that has never once asked you to produce force quickly. That is the specific thing that has been declining, and it is the specific thing that is not being trained.
This page is training guidance, not medical advice. If you have a heart condition, a significant injury history, or you have been inactive for years, get cleared before starting explosive work.
Questions on this
Can you build muscle after 40?
Yes. The study most relevant here found men averaging 71 increasing type II fiber size by 24% over six months of resistance training. Building muscle at 40 is not a marginal case, it is comfortably within what training reliably does.
Is 40 too late to start sprinting?
No, but the on-ramp is not optional. Tendon adapts slower than muscle, so the sensible version is a few weeks of hill work at submaximal effort before any flat-out running. Almost all sprint injuries in this group happen to people who skipped that.
How much of the decline is testosterone?
Some of it, and how much varies enough between individuals that a website cannot tell you. It is a blood test and a doctor's conversation. Worth knowing separately: the training described here is the kind that most strongly signals the body to keep muscle, whatever your levels.
I have not trained in ten years. Where do I start?
With the easiest version of the right thing rather than a hard version of the wrong thing. Get cleared if you have any reason to, then build a few weeks of basic strength work and hill efforts before anything maximal. The first six weeks are about tissue tolerance, not performance.
Will I ever get back to how I was at 25?
Possibly not identically, and it is the wrong target anyway. Most men at 43 were not training well at 25, they were simply young. Training the fast fibers properly now is a different proposition from repeating what you used to do, and for a lot of people it produces a better body than they had.
Where the numbers come from
- 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%.
- 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.
Read next
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