By sport
Cross-Country Skiing Training Zones
The Nordic federation I1–I5 intensity model, anchored to heart rate and lactate. Huge 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, while the classic 220 − age runs high. At age 35 that is roughly 184 and 185 bpm, but the real value varies by ±10–12 bpm, so test it to be sure.
Heart Rate Zone Calculator
Your 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 key aerobic-base zone, runs about 111–130 bpm. Spend most easy training 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 a 190 bpm maximum, I1 runs 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.