By sport
Cross-Country Skiing Training Zones
The Nordic federation I1–I5 model, anchored to heart rate and lactate. Big volumes of easy I1–I2 underpin the sport.
Max Heart Rate Calculator
Your maximum heart rate is the highest your heart can beat at all-out effort. Age formulas estimate it: Tanaka gives 208 − 0.7 × age, the classic 220 − age runs high. At age 35 that is 184 and 185 bpm, but true values vary by ±10–12 bpm, so test it.
Heart Rate Zone Calculator
Heart-rate zones are percentages of your maximum heart rate: Zone 1 is 50–60%, Zone 2 60–70%, Zone 3 70–80%, Zone 4 80–90% and Zone 5 90–100%. At a max of 185 bpm, Zone 2, the aerobic-base zone, is 111–130 bpm. Most easy training belongs in Zones 1–2.
XC Skiing & Biathlon Heart Rate Zones (I1–I5)
Cross-country skiing and biathlon use the Norwegian/FIS I1–I5 scale: I1 is 60–72% of maximum heart rate (<2 mmol/L lactate), I2 72–82% (~2), I3 82–87% (2.5–4), I4 87–92% (4–6) and I5 92–100% (>6). At 190 bpm maximum, I1 is 114–137 bpm and I3 156–165 bpm.
Carbohydrate Intake Calculator
Fuel by duration. Under an hour, water is usually enough (0 g/h). From 1 to 2.5 hours, aim for about 60 g of carbohydrate per hour from a single source. Beyond 2.5 hours, you can absorb up to 90 g/h using a glucose-to-fructose mix near 2:1. A 2-hour session needs roughly 120 g total.
Sweat Rate Calculator
Your sweat rate is the fluid you lose per hour of exercise. Weigh yourself before and after a session, add any fluid you drank, and divide by the time. Lose 1 kg in an hour while drinking 500 ml and your sweat rate is 1.5 L/h. On long efforts, replace roughly 100% to 150% of it.