Healthy living

Twelve weeks of training nudged muscle genes in older adults; a berry extract added nothing

In a small randomized trial, 38 adults aged 55 to 70 did strength training plus short bursts of hard cycling for 12 weeks, taking either a blackcurrant and redcurrant extract or a placebo. Training changed the activity of a modest number of muscle genes, mostly by small amounts; the extract made no meaningful difference.

Exercise is one of the best-supported ways to keep muscles strong as we age. What happens inside the muscle when it adapts is less clear. One way to look is to read which genes a muscle switches up or down after weeks of training. A second question often comes with it: can a supplement make that response bigger? Polyphenols, plant compounds found in berries, tea and cocoa, are often promoted for this.

A randomized trial in middle-aged and older adults put both questions to the test. Earlier reports from the same trial had already found that training improved muscle mass, strength, fitness and the function of mitochondria, the cell's power plants, and that the polyphenol extract did not add to those gains. This new paper looked one level deeper, at gene activity in the muscle itself.

What they did

Forty-one adults aged 55 to 70 (21 men, 20 women) completed the full study. They were randomly assigned, double-blind (neither they nor the testers knew who got what), to a daily extract of red and blackcurrants, providing about 700 mg of polyphenols, or to a placebo.

  • First 30 days: supplement or placebo only, no training.
  • Next 12 weeks: supervised training with full-body weight training twice a week plus one session that combined leg strength work with 7 to 9 minutes of high-intensity interval cycling. The supplement or placebo continued.
  • Muscle samples: small biopsies from the front thigh muscle were taken just before and just after the 12 weeks. After quality checks, 38 people had usable samples at both times: 17 on the extract and 21 on placebo.

The team then measured the activity of thousands of genes at once (RNA sequencing), and took into account each person's age, sex and their mix of slow and fast muscle fibres, which turned out to shape gene activity far more than age did.

What they found

  • Training changed gene activity, but modestly. Comparing before and after in everyone together, 60 genes changed reliably. Only seven changed by at least a factor of two, and most changes were small.
  • Some changes made sense. Among those that rose was LOX, a gene for an enzyme that cross-links collagen in the scaffolding around muscle fibres. One that fell was MYH1, which codes for a protein in the fastest-contracting muscle fibres. But the changes did not add up to clear shifts in whole biological pathways.
  • The extract did not change the picture. A handful of genes behaved differently in the two groups, but these genes were barely active and varied a lot from person to person. The authors conclude the supplement "did not meaningfully" influence the muscle's response to training.
  • Men and women responded alike at the gene level, as far as this study could tell.

What to keep in mind

  • Small numbers. The authors say the sample size may have limited their power to detect small but real changes.
  • Weak RNA. The quality of the RNA from the biopsies was relatively low, which the authors say may have hidden some changes and added noise.
  • A blurred view. The method averages over all cells in the sample, so changes in one cell type can be missed, and gene activity doesn't capture everything: muscle also adapts by changing how much protein it makes from existing instructions.
  • Few genes ≠ little benefit. The same people did get stronger and fitter. A quiet gene readout says more about how muscle adapts (many small tweaks) than about whether training works.
  • One extract, one dose. The trial tested a single blackcurrant and redcurrant product. It says nothing about other polyphenols, foods or doses.

Why it matters

Supplements are often sold with the promise that they boost the benefits of exercise. In this double-blind trial in people aged 55 to 70, a polyphenol extract added nothing measurable, either in the earlier reports on strength and fitness or now in the muscle's gene activity. The training itself did the work. The finding that exercise reshapes muscle through many small adjustments rather than a few big switches also fits what other recent studies have reported, and it is a reminder that a modest-looking gene signal can sit behind clear improvements people can feel.

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