Dear Reader,

I remember learning about energy systems in school. Professor Paul Gastin's diagram was the gold standard: a clean picture of how much each system contributed depending on effort duration. You've probably seen similar. ATP-PCr, Glycolysis/lactic, Aerobic; each with its lane, each with its moment.

Then I watched a film that added the piece Gastin hadn't for me. That these systems are never one or the other. Instead they're always working together, just with one more dominant than the others at any given moment.

But here's what neither the textbook nor the film could show you: that dominance doesn't just depend on how long or how hard the effort is. It depends on everything that came before it. A 30-second sprint in a fresh warm-up and a 30-second sprint in the final hour of a stage race are not the same metabolic event. The history of what you've done changes which system is running the show in any given moment.

That's the gap that Dr Andrea Zignoli and the team have been working to close for over four years. And today, for the first time, you can actually see it. In any of your Athletica sessions. The new Athletica System Engagement feature shows you which metabolic domain is running the show at any point in your training or racing, and how hard it's being pushed relative to your personal best.

Most of that four-year journey belongs to Andrea, whose mathematical rigour turned an idea into something peer-reviewed and published today in the European Journal of Sport Science. He and the team used 10 days of training data from 21 professional cyclists to build individual power profiles, then tested the model on a single final day: a fatiguing protocol of around 2000 kJ of work followed by 3-minute and 12-minute maximal time trials, to evaluate how accurately it predicted performance limits. The finding that surprised us most: when riders went maximal, the dominant system wasn't the one you'd expect from the effort duration. It was a much slower aerobic timescale, around one hour. What came before governed the ceiling. Gastin couldn't show us that. But today thanks to Andrea's innovation, we now can.

Here's what it means for you: If you have a power or pace profile in Athletica, go to your recently completed training session, click on 'Analysis', hit 'Advanced Metrics' and find 'System Engagement'. Ask the question: what was actually working hardest? What was the bottleneck?

One honest note: the model runs on external load; power or pace. We're inferring the internal metabolic picture, not measuring lactate or VO2 directly. We say that clearly in the paper, and we say it here. But it's the most mechanistically grounded read of your session you'll get from a power or pace file.

Read the case study from team Bardiani-CSF 7 Saber at the Giro d'Italia and Baku-Khankendi Azerbaijan, with additional System Engagement details.

Read the peer-review paper in the European Journal of Sport Science.

More on this exciting Sports Science 3.0 innovation soon.

All systems go!

Paul Laursen, PhD