A terrible, no-energy race isn't always about pacing

By Raph · July 20, 2026

We just released Runsense 1.5. In it, you'll find a new tab: Trends. It shows the training and recovery metrics your coach reasons from:

• Performance: your fitness, form, and fatigue over time, so you can watch your build take shape.
• Health: HRV, resting heart rate, and sleep, each plotted against your own normal range.
• Training: your recent effort at a glance.

Race day approaches: Two Runsense athletes will be running the Never Summer 100k this Saturday, and I'm one of them! This'll be the longest distance I've ever done, so wish me luck!

Coach's Corner: why a terrible, no-energy race isn't always about pacing.

A race that falls apart in a way your training didn't predict (flat legs, no energy, maybe walking for the first time) isn't always a pacing or fueling-that-day problem. If it comes with two other things, losing weight without trying, and a resting or easy-run heart rate that's crept up even though your fitness should be improving, all three are usually symptoms of the same problem: your eating hasn't kept pace with your training load.

Any one of those alone doesn't mean much. One bad race happens. Some runners naturally lean out as mileage builds. Heart rate creeps for plenty of reasons. But together, a flat no-energy race, unintended weight loss, and a rising easy-day heart rate usually point to one cause, not three.

This is what sports medicine calls low energy availability, and it's not just a performance issue. A 2025 meta-analysis of over 6,000 athletes found it's linked to worse endurance performance and higher rates of bone stress injuries like stress fractures (Gallant et al., 2025, Sports Medicine). The 2023 IOC consensus statement on Relative Energy Deficiency in Sport (REDs) describes it as a spectrum, where a bigger, longer-running deficit is what turns a harmless dip into a real problem (Mountjoy et al., 2023, British Journal of Sports Medicine).

The fix is usually more food, especially carbs, especially on hard days. If you experience symptoms like missed periods, frequent injuries, or persistent fatigue, have a conversation with your doctor or dietitian.

Training should make you stronger and set you up for a race that matches your fitness. If instead you're losing weight and your races are getting worse, that's likely an energy availability problem. More on daily nutrition for runners.

This started as a post over on r/runsense, our little corner of Reddit. Come hang out: When a Bad Run Isn't Pacing or Fueling: Low Energy.

— Raph