physical · Outcome
Time to exhaustion at a given workload, or total work completed in a session. The functional output of fitness; closer to 'how long can you keep going' than 'how big is your engine.'
How to measure: Time to exhaustion at a fixed pace, lift-weight progression, time trials over a known route. Wearable training-load metrics are loose proxies.
Three levers, one stack. Each works through a different mechanism. They compound.
Meaningful
4-6 g daily, split into 2-3 doses · Any time; loading window is 4-8 weeks
Effect size
Corpus
6 papers
3 small · 6 moderate · 0 large · 1 unclear
“The supplement demonstrates a short-term neuroactive effect in primary open angle glaucoma patients as indicated by improvement of Pattern Electroretinogram amplitude and foveal sensitivity.”
Why: Raises muscle carnosine, which buffers acid during high-intensity work. Effect is real and consistent in the 60-240 second window. Tingling at high doses is harmless but uncomfortable; split into 2 g portions to avoid.
See the studies+44% capacity
180-300 min weekly at conversational pace · 3-5 sessions across the week
Effect size
Corpus
29 papers
range 41–44 · n=3 quantitative claims
“Performing resistance training before endurance training may favor strength gains in concurrent training.”
Why: Most amateurs do all their training at 'medium hard,' which builds nothing. Polarized training (mostly easy, occasionally very hard) raises capacity faster than the middle-pace grind.
Meaningful
150-200 g 2-3 hours pre-session · Pre-training or pre-event
Effect size
Corpus
33 papers
10 small · 15 moderate · 0 large · 9 unclear
“Beetroot-based supplements produced a small positive effect on muscular endurance in healthy males (SMD 0.31, 95% CI 0.10-0.51).”
Most direct food-as-ergogenic in the corpus. Whole beets work; concentrated juice works faster and at lower volume but costs more.
Everything we found, ranked by how strongly we recommend it. Tap any to see the studies.
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The one we recommend first
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Evidence-backed alternatives or additions
Worth considering
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Every pick has two signals. They answer different questions and we never bundle them into one number.
Effect size
How big is the change on exercise capacity, in the units that matter for this outcome.
Confidence
How sure are we the effect is real for exercise capacity, given the studies we have.
For every pick, the “papers” number is how many studies we've cataloged that test this entity for exercise capacity. “Favorable” means the study reported the direction you want.
The tier badge (S, A, B…) on the entity itself is its overall research confidence across all outcomes. It's the same letter wherever you see this entity on the site, not specific to exercise capacity.
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