Older men's muscles answered weight training in the same direction as young men's, only more quietly

Muscle mass tends to peak somewhere in our twenties or thirties and then slowly declines, faster after about 60. Lifting weights, or resistance training, is one of the best-known ways to build or keep muscle, but older people usually gain less muscle from the same effort than younger people do. Why that happens inside the muscle is still not well understood.

A team at Auburn University in the United States looked at this from the angle of proteins, the molecules that do most of the work in a cell. They asked whether older muscle is less able to change its mix of proteins in response to training, a property the team calls "proteome plasticity". The proteome is the full set of proteins in a tissue.

What they did

The study reused muscle samples from three earlier training studies at the university. It included 17 younger men (average age about 22, range 19 to 26) and 15 older men (average about 57, range 42 to 69). None had done structured weight training in the previous six months.

• Training: everyone trained twice a week for 10 to 12 weeks under supervision, with leg exercises such as the leg press and squats or deadlifts plus upper-body pressing and pulling.
• Muscle size: lean body mass was measured with a DXA scan (a low-dose X-ray that separates fat, bone and lean tissue), and the thickness of the vastus lateralis, the large muscle on the outer front of the thigh, with ultrasound.
• Proteins: a small needle biopsy took a sample of that thigh muscle before training and at least three days after the last session. The team measured the dissolved (soluble) proteins with mass spectrometry, a machine that identifies proteins by weighing their fragments very precisely. After quality checks, 2,106 proteins were kept for analysis.

What they found

The two groups lifted a similar total amount, yet their results differed.

• Less growth with age. Both groups gained lean mass, but the younger men gained more: about 2.7 kg against about 1.2 kg. Thigh-muscle thickness rose by about 0.5 cm in the younger men and 0.2 cm in the older men. The younger men also improved their deadlift more and grew their fast-twitch (type II) fibres more.
• A much quieter protein response. Using a strict statistical test that guards against chance findings among thousands of proteins, training changed 135 proteins in the younger men and none in the older men.
• Same direction, smaller steps. Of those 135 proteins, 110 (81.5%) moved the same way in the older men, just by less. The typical size of the protein changes was also smaller in the older group.
• Protein factories still responded. Looking at groups of related proteins rather than single ones, 75 groups changed with training in the older men. The strongest were proteins for building new proteins, such as parts of ribosomes, the cell's protein-making machines.
• One clear difference. In the younger men, training lowered proteins of the energy-making machinery in mitochondria, the cell's power plants. This drop was almost absent in the older men.
• Older muscle started out different. Before training, 278 proteins differed between the age groups. Some proteins of the muscle's contracting units were lower in the older men, and some proteins for burning fat were higher.

The team calls this a "compressed" response: the same changes, only weaker.

What to keep in mind

• The authors' own limits. The groups were small, which gave the study little power to detect effects in the older men; the team says the complete lack of significant protein changes there probably reflects both a weaker response and too few people. All participants were men, so the results may not apply to women. Only one thigh muscle was sampled, and only once after training, so the timing of the changes is unknown.
• Not that old. The "older" men averaged about 57 years, younger than in many aging studies; the authors note the effects might be larger in people over 65.
• Pooled studies. The samples came from earlier studies that gave different supplements (peanut protein and beetroot juice), and each supplement was tied to one age group, so differences between the original studies can't be fully separated from age. The older men also carried more body fat.
• Age groups, not aging. Comparing different people may partly reflect generational differences rather than aging itself.
• "Reversal" is unproven. Training in the older men tended to push many proteins opposite to the age difference. But because both comparisons use the same pre-training samples from the older men, some of that pattern is built into the maths; the authors call it "hypothesis-generating".
• No predictor found. Protein patterns before training clearly told the age groups apart, but none reliably predicted how much muscle a person would gain.

Why it matters

Age-related muscle loss, or sarcopenia, affects up to 45% of adults over 70 according to figures the authors cite, so older muscle's weaker response to training matters. This study suggests that the response in middle-aged and older men is not broken or rewired but turned down in volume, with the protein-building machinery still answering the call. If that holds in larger and older groups, including women, the authors argue it would favour approaches that strengthen the existing response rather than try to change its direction.