Tour De Ski Legkov's pulse

His pulse probably was lower earlier in the race, and ramped up toward the end. Same thing happens with running, even if the pace remains constant.

JAXDUKE wrote:

It seems to me ... that it would be difficult to operate at 90% of one's max for 81 minutes.

That is entirely possible and feasible.

If it was the British Eurosport commentators, they have a basic 1980's view of exercise physiology. Watch the 9k TDS final if you want to hear the phrase "lactic acid" about 500 times.

If HR gets higher during skiing, it's because oxygen consumption of a muscle group is self-limited by the presence of an acid threshold. More muscle groups are used in a full-body exercise than running, so they can use more oxygen overall without acidosis.

Single-arm-curl a light dumbbell and you will exceed your biceps's O2 max and drive it into acidosis while hardly raising your HR at all.

As a competitive nordic skier and runner I can say a xc ski race is much more like a fartlek workout than a track race. It's not uncommon that several times during a ski race an athlete will be pushing their max HR very high. Since, unlike running, skiing downhill requires little energy, skiers will push very hard at certain points in a race, to be followed by a downhill section which will allow them to recover.