How Revay works, and the evidence behind it
What Revay is
We call Revay the training companion that treats you like a human. This page is where we show our working.
Revay is a wellness app. We adapt your training and nutrition to what your body and your life are telling us: how tired you are, how you slept, where you are in your cycle if you’ve chosen to share that, any injury or illness you’ve logged, and the reality of a week with a job, a family, and commitments that sometimes need to take priority over your training.
We don’t diagnose anything, detect anything, or judge anything. We never decide that you’re injured, ill, or unfit to train. We respond to what you tell us, and sometimes we respond by adjusting training.
Every guide on this site that touches training, sleep, hormones, injury or illness starts from the reasoning on this page. The science here will keep moving, and we’ll move with it. What won’t change is what we’re building around: training that fits the life you actually have.
We build your plan around your life, not despite it
When we build your plan, we ask how you train now: the Tuesday spin class, the friendly club run you never miss, the Wednesday lunchtime swim because that’s when the pool is quiet. We build around those commitments as you tell us about them, and we don’t overwrite them with our own idea of your week, because a plan that ignores the life it has to live inside is destined to fail.
And when life moves, the plan moves. You missed a session because work ran over or a child was ill. That is not a failure, and we will never treat it as one. We reorganise the week around what actually happened and show you the path forward. Most training tools quietly assume you’re a machine that runs the same every day. Just because you missed a session, doesn’t mean you failed the plan. When a plan can’t bend to that, the plan has failed you.
How daily adaptation works, and when it doesn’t happen
Your day starts with a check-in. You log fatigue on a scale of 1 to 5, along with sleep, cycle information if it’s relevant to you, and anything else you want the plan to account for.
From there, if your signals are suggesting you would benefit from a different type of session, or an adaptation to your planned session, we’ll make the recommendation. Your plan is the default. We change it only when your body or your week tells us something the plan couldn’t have known, from the signals you give us.
A rough night’s sleep on top of high fatigue reduces the proposed load more than either would alone, because stress in a body multiplies rather than adds. And if the whole picture says today’s planned session is the wrong session, we propose swapping it: a recovery session in place of intervals, for example.
The evidence behind it
Published research and established sports science sit behind every rule in our engine. On this page you’ll find more information about the scientific principles upon which we’ve built Revay’s adaptation engine.
Your fatigue score guides every daily decision. Research validates self-reported fatigue as a reliable predictor of training readiness. Dr Stacy Sims’ work (2024) also shows that how well recovered your nervous system is, which researchers measure as heart rate variability, shifts with your hormones across the cycle. Your fatigue score is the everyday signal for that same physiology, which is why it comes first.
Sleep is important. In the second half of the cycle, roughly from a week after ovulation until your period, sleep gets measurably worse: less of the deep, restorative kind, and longer to drop off (Sims, Huberman Lab, 2024). That’s why sleep compounds with fatigue in Revay’s adaptation engine.
Cycle-phase adaptation follows the modern framework, not the rigid one. We draw primarily on Sims’ published work, including ROAR (2016) and her 2024 writing on cycle-informed training, alongside the International Society of Sports Nutrition’s position stand on female athlete nutrition (Sims et al., 2023). The principle is that the best approach is to individualise from your data, not prescribe from a calendar. In Revay, your cycle phase adjusts the range of a proposal, but how you actually feel in the moment is the governing factor
Energy and nutrition come from established calculations. We calculate the energy cost of your training using the Compendium of Physical Activities (Ainsworth et al., 2011), the standard reference for how much different activities demand. Carbohydrate scales with your training load, following the fuel-for-the-work-required framework (Burke et al., 2011): more fuel on the days that need it, less on the days that don’t. Protein targets by age and session type draw on the ESPEN expert group’s recommendations for ageing muscle (Deutz et al., 2014) and the ISSN position stand above. And we always derive calories from your protein, carbohydrate and fat targets as an output. We never set a calorie target directly, a deliberate guard against the calorie-first pattern associated with disordered eating.
Illness follows the rule sports medicine actually uses. If you log an illness, we follow the above-the-neck, below-the-neck rule described in USA Triathlon guidance, Cleveland Clinic sports medicine material, and the 2024 review literature on exercise during viral respiratory illness. Symptoms only above the neck, like a runny nose or sore throat, may be compatible with light movement. Anything below the neck, like fever, chest symptoms or body aches will prompt rest as the adaptation.
Injury substitutions come from clinical practice guidelines. We hand-built our conditions library from sources including the Journal of Orthopaedic and Sports Physical Therapy’s clinical practice guidelines and recent systematic reviews. We use it to help adapt your training based on what you’ve logged. Revay is not a medical solution, and you should always consult a medical professional when undertaking structured training, including when you have been injured or ill.
We don’t infer anything about any of these sources beyond what they show. Where a rule rests on well-evidenced direction but estimated magnitude, we tag it that way internally.
What we will never do
We don’t diagnose, detect, or grade anything. Injury and illness exist in Revay because you logged them. We will never claim to have assessed a condition, tell you how serious it is, what it might be, or how long it will last.
We don’t tell you whether you’re well enough to train. That judgement belongs to you and, where it matters, to your GP or clinician. We adjust training in response to what you’ve declared, and you choose to accept each adaptation.
We don’t apply cycle logic to anyone it wouldn’t be valid for. We apply phase-based adaptation only if you have a naturally occurring cycle, including if you use a copper IUD. If you’re on combined hormonal contraception, or in perimenopause or post-menopause, you get a fatigue-led model with an overlay built for your actual hormonal state. The hormonal layer of Revay is opt-in, and you can switch it off entirely whenever you like.
We don’t override your schedule, so long as we can help it. We build around the sessions which matter to you and make sure your Revay plan fits your life. You are much more likely to reach your potential with a plan that suits you.
We don’t publish training plans. A static plan can’t know how you slept last night or what your week looks like, and pretending otherwise is the industry habit we exist to reject. Our guides teach you how to make the right decisions for you and your training; we’re not here to lecture you on schedules.
Known gaps in our current methodology
Self-reported data is imperfect. A fatigue score is a snapshot filtered through mood, memory and habit. It’s the best daily signal available, but it relies on each Revay user being honest with where they’re at.
Individual variation is large, and there is still so much more research to do. The evidence on how the menstrual cycle affects performance is mixed: three of five systematic reviews examined in a 2023 analysis (Colenso-Semple et al., Frontiers in Sports and Active Living) found no measurable effect of cycle phase on strength performance, and effects across studies are generally small. This is exactly why we treat your cycle as context that adjusts a range, never as a rule that overrides how you feel.
None of this weakens the case for adapting training; but it defines how to do it honestly: lead with the signals that we trust, and let your own knowledge of your body inform how your training moulds to your life.
How each discipline is built
This page covers the adaptation layer: the daily reasoning that runs across everything we do. Beneath it, each discipline has its own methodology, from how we periodise a running plan to how we structure and progress strength work. Each discipline has its own deep, distinct principles guiding the plans that Revay’s users train to; augmented by the principles of adaptation that makes each plan unique.
Review and revision
The Revay team last reviewed this page internally in July 2026, against the sources listed above.
If you want more information about anything you see here, or you have questions, you just want to chat about it, get in touch at hello@revay.app. To hear about our beta launch, sign up using the form below.