For ultra-endurance athletes, fresh fitness is only half the story.

Exhaustion after an intense cycling stage at TCR#12 is evident whilst i rested on the pavement.

Fresh FTP, VO₂max and threshold matter. But in ultra-endurance racing, the more important question is: what remains after several hours?

That is the thinking behind my Sparks Into Life Durability Index. I look at how power, heart rate, RPE, efficiency and threshold-related performance change after a prolonged endurance load. Two athletes can look almost identical when fresh and be completely different five hours later.

In my own preparation for events like the TCR, I progressively build this durability rather than simply chasing higher FTP. A typical build might include one quality VO₂/threshold session, substantial easy aerobic work, and a progressively longer endurance ride each week. As the event approaches, I introduce back-to-back long days and occasionally place controlled tempo or climbing work late in the ride, when fatigue has already accumulated.

Taking a break

Fuelling is part of the durability equation too. The recent attention around Tadej Pogačar using lactate-containing fuel is fascinating because lactate is increasingly understood as an oxidizable fuel rather than metabolic waste. Reports suggest it may provide an additional intestinally absorbed energy source alongside carbohydrate.

But I would not rush athletes onto lactate products yet. Elite practice is ahead of the evidence. The practical priority remains high carbohydrate availability, gut training, hydration and pacing.

For male and female ultra-athletes alike, the lesson is simple: train the athlete you will be after six hours, not just the athlete who starts the race. Women may also demonstrate different fatigue and substrate-use characteristics, so durability testing and fuelling should be individualised rather than copied from male data.

That is where I see endurance coaching moving: profiling not only how powerful an athlete is, but how well that physiology survives prolonged work.

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