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LONGEVITY LATEST ISSUE 29 · 23 SEPTEMBER 2026
LONGEVITY LATEST
The Evidence-Based Edge on Living Longer and Better
Issue 29 · Strength in Reserve · 23 September 2026
WELCOME
Welcome
Sit on a firm chair, fold your arms and stand up five times as quickly as you safely can. Time it. That number says more about your reserve than the lean-mass figure on a body-composition scan.
Your scan and your stopwatch can tell different stories. Most people only ever look at the scan.
They drift apart for a reason. In the Health ABC study, older adults lost leg strength about three times faster than leg lean mass. This week we grade three ways to protect muscle during weight loss, and test the claim that weight-loss jabs ‘melt’ it.
SPOTLIGHT
Size, strength and function are different numbers
Measure | What it tells you | What it cannot tell you |
Lean mass (DXA or smart scale) | How much non-fat, non-bone tissue you carry. | How much of it is muscle, or what that muscle can do. |
Strength (grip, leg press) | The force your muscles can produce today. | Whether gaining it adds years. That link is observational. |
Function (chair stands, gait speed) | Whether strength turns into everyday movement. | Which link failed: muscle, nerve, joint, balance or heart and lungs. |
The global sarcopenia consensus (GLIS, 2024) now treats mass, strength and strength per unit of muscle as separate components, with physical performance as the outcome. Health ABC showed why: in 2,292 adults aged 70 to 79, low strength predicted death, and low muscle mass did not explain it.
Goodpaster et al. Health ABC (2006) · Newman et al. Strength, not mass (2006) · Kirk et al. GLIS definition. Age and Ageing (2024)
Mass is the raw material. Strength and function are the reserve you actually spend.
THIS WEEK’S ANALYSIS
Top 3 Interventions Under the Microscope
The grades judge evidence for preserving muscle and function during weight loss, not for adding years.
Muscle-evidence grades: A = replicated trials on strength or function; B = consistent effects on muscle mass, weaker on function; C = early or single-trial human data; D = insufficient human evidence.
1. Resistance training during weight loss | Grade A
Lift at least twice a week while losing weight. It is the only option here with trial evidence on what the muscle can do.
Why. Across 25 randomised trials, adding resistance exercise to a diet protected fat-free mass and improved strength. In LITOE (NEJM, 2017), older adults with obesity who lifted lost 2–3% of their lean mass rather than 5%, gained roughly a fifth in strength, and improved most on physical performance when lifting was combined with aerobic work.
The limit. These were diet trials, not GLP-1 trials. LEAN-PREP is testing that combination now.
Binmahfoz et al. BMJ Open SEM (2025) · Villareal et al. LITOE. NEJM (2017) · LEAN-PREP protocol (2026)
2. Protein above the minimum | Grade B
Eat at least 1.0–1.2 g of protein per kg a day if you are older or dieting, spread across meals. Then train: protein alone moves the scan more than the stopwatch.
Fair warning: this is where the size–function gap shows most clearly. Pooled trials in adults over 50 find higher protein keeps more lean mass during weight loss. But a Dutch trial that supplied participants’ food found no difference in lean mass, leg strength or walking between 1.7 and 0.9 g/kg/day, and a 2026 analysis of 191 older dieters linked higher intake to more limb lean tissue, not better grip, gait or chair stands.
With kidney disease, agree a target with your clinician.
Kim et al. Nutrition Reviews (2016) · Backx et al. Int J Obesity (2016) · Eglseer et al. Nutrition Journal (2026)
3. Muscle-sparing drugs alongside GLP-1s | Grade C
Watch, don’t chase. These drugs protect tissue; nobody has yet shown they protect function.
Two antibodies reported Phase 2 results in Nature Medicine this year. On DXA, bimagrumab shifted semaglutide weight loss towards fat (BELIEVE, 507 adults), and apitegromab spared 1.9 kg of lean mass on tirzepatide (EMBRAZE, 102 adults). Neither has shown fewer falls or less disability, and bimagrumab, given by infusion, brought more muscle spasms, diarrhoea and acne.
HYPE CHECK
“Weight-loss jabs melt your muscle”
The claim. Up to 40% of the weight lost on GLP-1 drugs is muscle, so the drugs are making people frail.
The missing step. That figure comes from DXA ‘lean mass’, which counts water, organs and connective tissue alongside muscle. In mice on these drugs, the liver shrank more than muscle did. In SURPASS-3, MRI showed thigh muscle volume falling roughly in line with weight lost, while fat inside the muscle fell more than expected (a post hoc, industry-funded analysis).
None of the 36 trials in an April 2026 Annals of Internal Medicine review measured objective physical function.
That cuts both ways. The same review found muscle-related losses often exceeded expected benchmarks, and older or weaker people have least to spare. The concern is legitimate. The certainty is not.
Batsis et al. Annals of Internal Medicine (2026) · Sattar et al. SURPASS-3 MRI (2025) · Langer et al. Cell Reports Medicine (2026)
Our verdict. Don’t abandon a prescribed treatment over a lean-mass percentage, or buy a supplement stack to fix it. Measure function before you start and check whether it holds; if it falls, tell the prescriber. The stopwatch and the chair cost nothing.
IN BRIEF · NEW RESEARCH
Function can be protected, though not equally. A Nature Aging analysis published 31 August revisited SPRINTT: exercise plus nutritional counselling in 1,199 frail adults aged 70 or over with sarcopenia and multiple chronic conditions. The programme cut the risk of mobility disability or death (HR 0.78), with benefit clearest in milder or psychiatric disease patterns. The subgroups are post hoc hypotheses. The headline holds: function can move.
THIS WEEK’S DEEP DIVE
Strength Before Size
The strangest result in Health ABC: older adults who gained lean mass still lost strength. More muscle, less force.
The companion explains the biology behind that gap, whether strength actually buys years or merely signals good health, what evidence would upgrade each grade above, and how big a change in your own chair-stand or grip result must be before it means anything.
Read the companion: Strength Before Size →
BIOHACKING CORNER · THE SHORT VERSION
Run your baseline this week. Chair stand: a standard-height chair against a wall, arms crossed, feet flat. Stand fully and sit fully five times as quickly as you safely can, and stop the clock on the fifth stand. Grip, if you can borrow a dynamometer: elbow bent at 90 degrees, best of two attempts, same device every time. Log the time of day, footwear and chair.
My rule: same test, same conditions, every time. Before you read anything into a retest, check the companion for how big a change counts as real. If you cannot stand without your hands, or the test causes pain or dizziness, stop and speak to a clinician.
READER PULSE
Once you have run the chair test, reply with two things: the number you had been tracking until now, and whether the stopwatch told you something different.
CLOSING
Keep the reserve you will need later
Muscle mass is raw material. Strength is what the material can do, and function is whether you can still use it on a bad day, after an illness or at 85. Ageing, dieting and the new weight-loss drugs all draw on that reserve. The evidence favours an unglamorous response: measure it, load it, feed it.
Next week: bone, the quieter tissue that weight loss can also thin, and what a DXA T-score can and cannot tell you.
Stay curious and stay healthy!
Christian Thomsen, Editor
Longevity Latest is published weekly by FrontWave Media Ltd. Educational content, not personal medical advice. Do not change a prescribed weight-loss medication on the basis of this issue. With heart, joint, kidney or balance problems, check with a clinician before starting resistance training or raising protein.
Sources and reading notes
Evidence checked through 18 September 2026. Strength–mortality links are observational; bimagrumab and apitegromab are investigational.
Goodpaster et al. Health ABC: strength, mass and quality (2006) · Newman et al. Health ABC mortality (2006)
Kim et al. Nutrition Reviews (2016) · Backx et al. Int J Obesity (2016) · Eglseer et al. Nutrition Journal (2026)
© 2026 FrontWave Media Ltd · Longevity Latest
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