Longevity Next

Trial

MASTERS

Source-reviewed Last reviewed: 2026-10-02

Research Observatory

Evidence Update

Current evidence

MASTERS compared metformin with placebo alongside progressive resistance training in older adults. It found smaller whole-muscle/lean-mass gains with metformin, but no significant between-arm difference in the powered type-II-fiber endpoint or reported strength/power measures. A later analysis of the same participants suggests a statin-associated modifier of muscle-fiber growth under metformin, but does not establish a causal combination-therapy benefit or independent replication.

What changed

The accepted result preserves endpoint hierarchy, the corrected relative-strength comparison and the later nonrandomized statin-subgroup context.

What did not change

The study does not establish generalized harm from metformin, causal benefit from adding a statin or an independent replication of its own subgroup analysis.

Why it matters

Exercise exposure and endpoint scale are essential to interpreting this trial: whole-muscle findings cannot be substituted for the powered fiber endpoint or clinical function.

Main limitation

Strength1RM,p=.055, isometric,p=.082, power,p=.064: trends, not significant harm or equivalence. Corrected relative-strength gains18.9% versus14.8%,p=.30. No no-exercise arm; no generalization to all metformin use or frail/diabetic populations. Statin users differed in sex and other medication use; small and varying biopsy denominators, multiple comparisons, no randomized statin assignment. Cannot reverse the whole-cohort result.

Next proof

Independent prespecified drug-by-exercise trials with clinically relevant function and adequately powered interactions. Prospectively randomized factorial or stratified trial testing the interaction.

Evidence reviewed through

Evidence release LNPG-REL-20261002-001

Sources

  1. Metformin blunts muscle hypertrophy in response to progressive resistance exercise training in older adults: The MASTERS trial

    Source type human_parallel_randomized Publication date 2019-09-26

    What this source establishes Reports muscle-mass, fiber-size and strength comparisons for metformin versus placebo during MASTERS resistance training.

    Important limitation Endpoint hierarchy matters: the powered fiber endpoint and reported strength/power comparisons were not significant; use the corrected relative-strength values.

    Evidence access Relevant full-text sections reviewed.

  2. MASTERS registry record

    Source type registry Publication date 2014-12-04

    What this source establishes Records MASTERS's enrollment and registered type-II muscle-fiber primary outcome.

    Important limitation Registered design does not itself establish a treatment effect.

    Evidence access Official registry record reviewed.

  3. Potential Benefits of Combined Statin and Metformin Therapy on Resistance Training Response in Older Individuals

    Source type secondary_analysis Publication date 2022-04-14

    What this source establishes Analyzes whether pre-existing statin use modified muscle-fiber responses in the same MASTERS participants.

    Important limitation Statin use was not randomized; small subgroups and multiple comparisons cannot establish causal combination benefit.

    Evidence access Relevant full-text sections reviewed.

  4. Metformin to Augment Strength Training Effective Response in Seniors (MASTERS): study protocol for a randomized controlled trial

    Source type protocol Publication date 2017-04-26

    What this source establishes Describes MASTERS's planned outcomes and statistical power for the muscle-fiber comparison.

    Important limitation Protocol evidence is not a result; its broader outcome list must be distinguished from the powered analysis.

    Evidence access Relevant protocol sections reviewed.

  5. Corrigendum to the MASTERS trial report

    Source type correction Publication date 2020-01-15

    What this source establishes Corrects the MASTERS relative-strength table and associated supplementary information.

    Important limitation Corrects the same experiment; it is not a new trial or replication.

    Evidence access Correction notice reviewed.

Summary

MASTERS trial intelligence: MASTERS found smaller whole-muscle/lean-mass gains with metformin during resistance training, but no significant between-arm difference in the powered type-II-fiber endpoint or reported strength/power measures. A later MASTERS reanalysis suggests a statin-associated modifier of muscle-fiber growth under metformin, but does not establish a causal combination-therapy benefit or independent replication.

Intelligence Take

Exercise exposure and endpoint scale are essential to interpreting this trial: whole-muscle findings cannot be substituted for the powered fiber endpoint or clinical function.

Limitations

Strength1RM,p=.055, isometric,p=.082, power,p=.064: trends, not significant harm or equivalence. Corrected relative-strength gains18.9% versus14.8%,p=.30. No no-exercise arm; no generalization to all metformin use or frail/diabetic populations. Statin users differed in sex and other medication use; small and varying biopsy denominators, multiple comparisons, no randomized statin assignment. Cannot reverse the whole-cohort result.

Opens in a new tab