331‒ Optimizing endurance performance: metrics, nutrition, lactate, & insights from elite performers

KEYPOINTS

• 01

  Threshold numbers are approximations, so test the same way every time

  FTP was originally a 5-minute all-out effort followed by a 20-minute all-out effort, minus 5%. Many people now skip the first part, which changes the result. Critical power comes from several all-out efforts fitted to a curve, and usually sits between maximal lactate steady state and VO2 max. The various thresholds are often only a few percent apart, and the gap is bigger in power athletes than in endurance athletes. Bu says a single number throws away how long you can hold each power. Track your 1-, 5- and 15-minute bests and watch how the balance between them changes.

• 02

  Blood lactate depends on dilution as well as production

  Lactate is produced all the time, even during sleep. A test only shows a 'threshold' once muscles release more than they clear. Hematocrit can change by more than 10% within a session from dehydration, and elite athletes have larger plasma volumes, so they may produce more lactate and still show lower concentrations. In elite marathoners and triathletes, the second inflection point (confirmed by maximal lactate steady state) can be below 2 mmol/L. The most useful definition is the point where lactate keeps rising at a constant pace.

• 03

  Elite endurance depends on how much of your VO2 max you can sustain

  Utilization is oxygen use at maximal lactate steady state, or at race pace, as a share of VO2 max. About 80% is unremarkable. Elite marathoners reach 94–95%, and Bu's triathletes are about there in Ironman racing. VO2 max itself falls over a long race, so the aim is to lose as little as possible. Keeping a very high VO2 max is costly: training 1- and 5-minute power takes away from race-specific work, and an oversized heart is less efficient at the effort that matters.

• 04

  Elite VO2 max is highly trainable

  Bu calls VO2 max the best practical single measure of health and performance, and says endurance capacity is better but impractical to test. Kristian Blummenfelt has exceeded 7.7–7.8 L/min at about 80 kg (about 100 mL/kg/min), and Gustav Iden reached about 94. Their VO2 max dropped when they moved from Olympic-distance training to Ironman training. Values across swimming, cycling and running started out clearly different and became almost identical as they trained to recruit more muscle in each.

• 05

  A good VO2 max test needs preparation and a set warm-up

  Eat as you would before a key session (carbohydrate), hydrate, sleep well, avoid soreness, and test at the same time of day because of circadian temperature changes. Bu's warm-up: 6 minutes very easy, 6 minutes at long-session effort, about 3 minutes near threshold by feel, then 2–3 efforts of 10–15 seconds with equal rest, for about 20 minutes in total. Then start the test without much delay. Peter adds that you have to be completely exhausted at the end, and many people aren't.

• 06

  Breath-holding can inflate a VO2 max reading

  Briefly restricting breathing near the end builds up an oxygen debt and can push a trained person's reading from 60 to over 70. Bu calls this cheating the protocol, not improved fitness. He also checks his metabolic carts against a lung simulator with reference gas, and in his lab the highest values often come on a second or third test about 10 minutes later.

• 07

  RQ tables mislead at high intensity

  Lactate can supply about 13–14% of energy if an athlete stays near threshold, while standard substrate tables assume it contributes nothing up to an RQ of 1.0. Bu is skeptical of them for endurance athletes from the low 0.90s. Threshold RQ also varies with athlete type: 0.96 is a common estimate, but extreme endurance athletes can be at 0.92–0.94.

• 08

  Fueling has advanced more than training

  Kristian and Gustav routinely absorb about 160 g of carbohydrate an hour, measured with carbon-13 tracers, and Bu has measured over 240 g. They drink about 1.4–2+ L an hour of a roughly 12% glucose-fructose mix (about 40:60) in a hydrogel, double the old 5–6% guideline. Bu says the gut is trainable and even honey can get you past published limits. They take no fat or protein during races, because carbohydrate gives the most work per unit of oxygen. Exogenous ketones can't be dosed high enough to fuel racing without making athletes feel as if they're bonking.

• 09

  Two elite athletes can respond very differently to the same aid

  Encapsulated bicarbonate (about 19–22 g, in a hydrogel to get past the stomach) produced Gustav's highest VO2 max. Some athletes nearly double their blood lactate on it, while Kristian's barely changes. Bu points to their very different blood and plasma volumes and stroke volumes: Kristian has more hemoglobin mass, and Gustav's maximum heart rate is about 200 versus about 170–180. At the elite level, one system ends up compensating for another.

• 10

  Bu prefers adapting the athlete to masking a limit

  He doesn't use high-dose acetaminophen for heat or pain, preferring that the body adapt to heat. Peter suggests testing it against placebo in alternating training weeks. Bu says the same oxygen logic applies to heat: every inefficiency adds heat and costs you late in the race. On cycling's post-doping speeds, both credit nutrition first, and Bu expects riders to get heavier again as underfueling is shown to limit adaptation.