Do Newbie Gains Still Happen After 40?

Morton and colleagues, pooling 49 randomized trials with 1,863 participants in the British Journal of Sports Medicine, found the fat-free mass benefit of protein supplementation fell by 0.01 kg per year of age, p=0.002. Peterson, Sen and Gordon pooled 49 studies of 1,328 adults over 50 in Medicine and Science in Sports and Exercise, reported a mean gain of 1.1 kg of lean body mass, and found older participants gained less, with a meta-regression coefficient of minus 0.03 at p=0.01.

Both findings point the same way. Neither is large. And here is the awkward part nobody mentions: almost none of this research studied people in their forties. The comparisons are twenty-somethings against sixty- and seventy-somethings, and the forties get interpolated.

Do newbie gains still happen after 40?

They do, and the trials are unambiguous about it. Frontera and colleagues trained twelve untrained men aged 60 to 72 for 12 weeks in the Journal of Applied Physiology. Knee extensor strength rose 107%, flexor strength 227%, quadriceps area 9.3%, and type I fiber area 33.5%.

Those are beginner-scale numbers in men decades past 40. Roth and colleagues ran six months of whole-body training on young and older men and women in the Journal of the American Geriatrics Society and found thigh and quadriceps volume rose significantly in every group with no significant differences between them.

So the honest framing is not whether the newbie phase exists after 40. It is how much smaller it runs, and the answer to that is less clear than you would expect.

What does the research on age and training response show?

It splits. Roughly half the well-controlled comparisons find an age penalty on muscle size and roughly half do not. The studies that find one tend to measure individual fibers or specific muscle groups. The studies that find none tend to measure whole-limb volume over longer periods.

How big is the age penalty in real numbers?

Small enough that it should not change your plan. Take the Morton coefficient literally. A 45-year-old and a 25-year-old differ by 20 years, so 0.01 kg per year makes a 0.2 kg difference in the fat-free mass benefit from supplementing protein. That is less than half a pound over two decades of age.

The fiber-level differences look bigger in percentage terms. Kosek and colleagues found mean type II fiber size rose 32% in the young group and 23% in the older group over 16 weeks in the Journal of Applied Physiology. Type I fibers grew 18% in the young group and did not reach significance in the older one.

But those comparisons pit 20-to-35 against 60-to-75. Nothing in that design tells you what happens at 43. We flag this kind of gap explicitly, which is covered in how we research.

Does the penalty hit every muscle equally?

No, and this is the most useful finding in the whole literature. Welle, Totterman and Thornton scanned nine young and eight older adults by MRI over three months of training, reported in the Journals of Gerontology. Elbow flexor area rose 22% in the young group against 9% in the older one.

Knee flexors showed the same pattern, 8% against 1%. Knee extensors did not: 4% in the young group, 6% in the older group. The quadriceps, the biggest muscle group most beginners train hardest, showed no penalty at all.

Welle’s group also found training-induced increases in specific tension, which is strength per unit of cross-sectional area, were equal in both age groups for elbow flexors and knee extensors, and actually larger in the older group for knee flexors.

The quadriceps, the muscle group most beginners train hardest, showed no age penalty at all.

Does strength respond differently from size after 40?

Strength holds up far better than size does. Fiatarone and colleagues trained frail nursing home residents averaging 87 years old for ten weeks in the New England Journal of Medicine. Muscle strength rose 113%. Thigh muscle area rose 2.7% and missed statistical significance.

That dissociation runs through the whole age literature. The strength curve after 40 is close to the strength curve at 25 for a beginner, because most early strength is neural rather than structural. The size curve is the one that flattens.

If you are judging progress by the mirror rather than the logbook after 40, you are watching the slower of the two variables. Our piece on how long results take at 50 separates those timelines properly.

Are there non-responders after 40?

Not according to the largest analysis that looked for them. Churchward-Venne and colleagues re-analyzed 110 adults over 65 at 12 weeks and 85 at 24 weeks in JAMDA, under the title “There Are No Nonresponders to Resistance-Type Exercise Training in Older Men and Women”.

Lean body mass rose 0.9 kg at 12 weeks and 1.1 kg at 24 weeks. The individual range was enormous, from minus 3.3 kg to plus 5.4 kg at 12 weeks. Every single participant improved on at least one outcome, and responsiveness improved with longer interventions.

Ahtiainen and colleagues found the same spread in 287 untrained adults aged 19 to 78 in Age. Mean muscle size change was 4.8%, individual results ranged from minus 11% to plus 30%, and age did not predict where anyone landed.

Does protein matter more after 40?

The evidence says it matters slightly less, not more, which surprises most people. The PROT-AGE position paper in JAMDA recommends at least 1.0 to 1.2 g/kg/day, and 1.2 g/kg/day or more for those exercising, but it was written for people over 65 and should not be read as a 45-year-old’s prescription.

For an exercising adult under 65, the ISSN position stand range of 1.4 to 2.0 g/kg/day applies at 45 exactly as it does at 25. Morton’s break-point analysis found no additional fat-free mass above a total intake of 1.62 g/kg/day at any age.

Getting there is a logistics problem, not a physiology problem. We cover the cheap version in hitting 150g of protein on a budget.

What should a 40-something beginner actually do?

Train as if the penalty does not exist, because at your age it barely does. Here is the judgement call: the age adjustments that dominate over-40 fitness content are almost all recovery advice, not stimulus advice, and lowering the stimulus is the one change the data does not support.

Frontera’s 60-to-72-year-olds trained at 80% of one-rep max, three sets of eight, three days a week, and doubled their leg strength in twelve weeks. Nothing in that protocol is gentle. Start there, add sets before you add days, and give the first block sixteen weeks before you judge it against how much muscle a 40-year-old adds in six months rather than against a younger lifter.

For the full picture on rate, read our pillar on how much muscle you can build naturally. If you are weighing whether to start at all, we answered that question directly, and lifting after 40 covers frequency and recovery.