Sweat rate, gut oxidation caps and protein thresholds.
Endurance hydration, intra-session carbohydrate fuelling and daily protein intake all obey measurable physiological ceilings: gastric emptying (~1.0 L/hr), intestinal SGLT1/GLUT5 transport (60 to 90 g/hr), and muscle protein synthesis saturation (1.6 to 2.2 g/kg/day). Test your numbers in the calculators below and read the exact equations underneath.
Endurance Hydration & Fuel · ACSM & Jeukendrup
Interactive Sweat Rate, Carbohydrate & Protein Calculators
Compute your hourly sweat loss, sodium concentration, intra-session carbohydrate band, and per-meal protein synthesis anchors.
30 to 60 g/hr (Single-source glucose/maltodextrin)
Jeukendrup (2014)
A general fitness estimate, not medical advice. Fluid, sodium and carbohydrate ranges are starting points, so drink to thirst too, and speak to a doctor if you have a heart, kidney or blood pressure condition.
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About these numbers: Formula, guard-rails & 2 peer-reviewed citations ▾
Sweat Rate (mL/h) = ((Pre kg − Post kg) × 1000 + Drank mL) ÷ Hours · Post-Session = 1.5 L per kg lost
Drink to replace most of your sweat, not more: drinking beyond what you lose can dilute blood sodium, so let thirst guide you too. The gut tolerates roughly 800 to 1,000 mL per hour during running, so if you sweat faster than that, start well hydrated and replace about 150% of the remaining deficit over 2 to 4 hours afterwards. Sodium and carbohydrate ranges are starting points, not prescriptions, and this is not medical advice.
• Estimating sweat rate from body weight before and after exercise, the two per cent body-mass dehydration threshold, and replacing about 150 per cent of the fluid lost after exercise come from the ACSM position stand on fluid replacement.
[Source]
• Hourly carbohydrate targets during endurance work scale with session duration rather than body weight: about 60 grams an hour for 2 to 3 hours, and up to about 90 grams an hour of multiple-transportable carbohydrates in ultra-endurance events, for well-trained athletes.
[Source]
The link carries the numbers you entered in the part of the address after the #, which is never sent to a server. Share it only with people you are happy to show those numbers to.
Embed This Calculator on Your Club or Coaching Site
About these numbers: Formula, guard-rails & 2 peer-reviewed citations ▾
Daily Protein = 1.6–2.2 g/kg (×1.12 if Plant-Based) · Meal Anchor ≈ 25–30g · Sleep starting point = 7.75h + 12 min per hard session a week (max 9h)
Spreading protein across your meals (roughly 0.3 to 0.4 g/kg per meal) is a common way to keep muscle protein synthesis topped up through the day. The plant-based adjustment and the sleep starting point are Pelaris rules of thumb, not figures from the papers, and none of this is medical or dietary advice for a health condition.
• Our protein guidance lands near 1.6 g per kg of body weight a day, the point this 49-study meta-analysis found extra protein stops adding muscle.
[Source]
• Sleep is treated as training, and this expert consensus is why we nudge you towards your own sleep need rather than a one-size-fits-all number.
[Source]
General fitness and training estimates only, labelled EST. Not medical advice or a clinical diagnosis.
1. Sweat-rate testing & the 150% rehydration rule (Sawka et al., 2007)
Individual sweat rates vary from 0.4 to over 2.5 litres per hour depending on intensity, heat acclimatisation, kit and genetics. Rather than guessing a generic water target, the ACSM Position Stand recommends calculating your personal sweat rate from a weighed training session:
Total Sweat Loss (mL) = (Pre-Exercise kg − Post-Exercise kg) × 1,000 + Fluid Consumed (mL)
Hourly Sweat Rate (L/hr) = Total Sweat Loss (mL) ÷ Session Duration (hrs) ÷ 1,000
Post-Session Rehydration (L) = Net Weight Deficit (kg) × 1.5 (consumed over 2 to 4 hours)
Endogenous muscle and liver glycogen is non-limiting
60 to 150 minutes
30 to 60 g/hr
Single-source glucose or maltodextrin via intestinal SGLT1
> 150 minutes (2.5h+)
60 to 90 g/hr
Dual-source glucose:fructose (2:1 or 1:0.8) via SGLT1 + GLUT5
2. Daily protein & meal leucine anchors (Morton et al., 2018)
Across 49 randomised trials in healthy adults performing resistance training, Morton and colleagues found that fat-free mass gains plateaued around 1.62 g/kg/day, with 2.2 g/kg/day covering the upper confidence interval for individual variance. In a calorie deficit, sports nutrition guidance often suggests 2.0 to 2.4 g/kg/day to help hold on to lean tissue. Read the full breakdown in Protein Intake for Strength Athletes, Post-Workout Nutrition, and Sleep for Athletes.
Sources on the shelf for this page
Estimating sweat rate from body weight before and after exercise, the two per cent body-mass dehydration threshold, and replacing about 150 per cent of the fluid lost after exercise come from the ACSM position stand on fluid replacement.
American College of Sports Medicine; Sawka, M.N., Burke, L.M., Eichner, E.R., Maughan, R.J., Montain, S.J. & Stachenfeld, N.S. "American College of Sports Medicine position stand. Exercise and fluid replacement." Medicine & Science in Sports & Exercise, 2007;39(2):377-390. doi:10.1249/mss.0b013e31802ca597
Hourly carbohydrate targets during endurance work scale with session duration rather than body weight: about 60 grams an hour for 2 to 3 hours, and up to about 90 grams an hour of multiple-transportable carbohydrates in ultra-endurance events, for well-trained athletes.
Jeukendrup, A. "A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Medicine, 2014;44(Suppl 1):S25-S33. doi:10.1007/s40279-014-0148-z
Our protein guidance lands near 1.6 g per kg of body weight a day, the point this 49-study meta-analysis found extra protein stops adding muscle.
Morton, R.W., Murphy, K.T., McKellar, S.R., Schoenfeld, B.J., Henselmans, M., Helms, E., Aragon, A.A., Devries, M.C., Banfield, L., Krieger, J.W. & Phillips, S.M. "A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults." British Journal of Sports Medicine, 2018;52(6):376-384. doi:10.1136/bjsports-2017-097608
Frequently asked questions: Hydration, fuelling & protein
Why does the calculator flag a 2 per cent body-mass loss?
The American College of Sports Medicine position stand on Exercise and Fluid Replacement (Sawka et al., 2007) identifies fluid loss of more than about 2 per cent of body mass as the point where aerobic performance can start to suffer, especially in the heat. It is a guide for planning, not a medical threshold.
Why do carbohydrate targets scale by session duration instead of body weight?
Asker Jeukendrup (2014) explains that carbohydrate taken during exercise is limited by intestinal absorption transporters (SGLT1 for glucose at about 60 g/hr, plus GLUT5 for fructose, up to about 90 g/hr combined in very long events) rather than by body size, so a 60 kg runner and a 90 kg cyclist have similar gut limits. The advice is aimed at well-trained athletes, and it is worth practising in training.
Why is 1.6 g/kg/day the protein anchor in the calculator?
Morton et al. (2018) meta-analysed 49 randomised controlled trials (1,863 participants) and found a statistically significant biphasic breakpoint at 1.62 grams of protein per kilogram of body weight per day, with 2.2 g/kg/day representing the upper 95 per cent confidence bound.
Why does sleep sit alongside protein and hydration?
The 2021 BJSM expert consensus on sleep and the athlete (Walsh et al., 2021) notes that athletes are prone to habitual short sleep (under 7 hours a night) and poor sleep quality, and that sleeping under 7 hours a night is linked with more respiratory infections in the wider population. It recommends an individual approach based on how much sleep you feel you need, rather than one number for everyone, so the calculator offers a starting point to adjust.
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