Sweat Rate Test (nutrition assessment, 5 steps, ~75 min)

What this is

The Sweat Rate Test is the seeded nutrition-domain assessment that measures fluid loss rate from a controlled weighed test. The result feeds the race-day fueling calculator as the bike or run sweat-rate input.

Domain: nutrition. Estimated duration: 75 minutes. Linked calculator: sweat_rate.

The 5-step protocol (as seeded)

1. Pre-weigh (~3 min): empty the bladder, towel dry, weigh nude. Record weight to 0.1 kg.
2. Exercise (60 min): train at goal race intensity in the conditions you want to characterise (temp + humidity matter). Track every mL of fluid you drink.
3. Towel dry (~2 min): wipe down thoroughly — sweat- soaked clothes weighed in skew the result.
4. Post-weigh (~3 min): nude, immediately after towelling.
5. Calculate — feed the four numbers into the sweat rate calculator.

The 60-minute exercise block is the minimum reliable duration. Shorter sessions hit pre-fueling hydration variance and produce noisy estimates.

Inputs the form asks for

• Pre-weight (kg).
• Post-weight (kg).
• Fluid consumed (L) — total during the exercise block.
• Exercise duration (min) — total time of the session, not including warm-up / cool-down outside the controlled block.

Outputs

• Sweat rate (L/hr) — computed as (pre_weight - post_weight + fluid_consumed) / duration.
• Total fluid loss (L) — sweat rate × duration.

Sodium loss is not an input or output of this assessment; the sweat rate calculator provides low/avg/high sodium estimates from the sweat-rate band as a separate output. If you have a real sweat-sodium lab test, enter the number into the fueling calculator's "Sweat Sodium" field directly.

When to retest

• Every 4-8 weeks during a build phase if conditions vary.
• When the race climate differs significantly from where you train (spring training in cool, race in heat).
• After heat-acclimatisation blocks.

Common gotchas

• Bladder not emptied pre-test — full bladder before, empty after, shifts the result by 200-400 g.
• Sweat-soaked clothes weighed — strip and towel dry.
• Inaccurate fluid tracking — measure bottles before the session; don't sip-count.
• Wrong intensity — sweat rate scales steeply with effort. Test at race intensity, not endurance pace.

See also: Sweat rate calculator, Race-day fueling calculator, Assessment model overview.