Study
Bryan Johnson promotes 4×4 interval training for cardiorespiratory fitness
NEW TRAINING PROTOCOL: Johnson promotes 4×4 intervals—4 minutes at 90–95% effort, 3 minutes easy, 4 repeats, 3+ times weekly for 8 weeks—but reports no personal outcome series.
Summary What is 4×4 interval training, and does it improve fitness? Show / hide ↓
4×4 interval training means four rounds of four minutes at 90–95% effort, followed by three minutes of easy exercise. It is intended to improve cardiorespiratory fitness, which means how well the heart and lungs supply oxygen during exercise. The suggested plan is at least three sessions a week for eight weeks. This record does not provide a personal series of results, so it does not show whether the protocol produced benefits in practice.
What this means for you: This is a clear exercise plan, but the available evidence here is weak. Do not assume it will improve your fitness based on this record alone.
weak evidenceOn 25 August 2026, Bryan Johnson posted a Norwegian 4×4-style interval prescription. He recommends more than 3 workouts per week for 8 weeks. Each workout has 4 minutes at 90–95% effort, 3 minutes easy, repeated 4 times. He states that the resulting improvement in cardiorespiratory fitness lowers all-cause mortality risk by 11%. The post does not identify the source study, give a sample size, define the mortality estimate’s population, or report his own baseline and follow-up VO2 max. The closest primary exercise literature supports short-term fitness improvements from interval training, but an 8-week personal protocol cannot demonstrate an 11% mortality reduction. A reply from Ryan Williamson, MD, calls 4×4 a well-validated way to improve VO2 max and reduce mortality, while other replies describe the 95% effort intervals as difficult. Those replies are commentary, not outcome data. This entry records a public training recommendation with an n=1 subject context, not a new randomized trial. The practical content is specific enough to reproduce, but the mortality statement is an extrapolation from population associations and prior studies rather than a measured result from Johnson.
Your improved cardiorespiratory fitness is the risk reduction.
No critic source this week tested Johnson’s specific 8-week mortality claim. The 4×4 protocol’s fitness literature includes a 40-man randomized exercise study, but it does not justify an ingredient evidence-grade change: https://pubmed.ncbi.nlm.nih.gov/17414804/.
From this page back to the goal it moves.
Cited by
2 encyclopedia entries reference this study.