Double Threshold Days

In endurance training, the concept of "threshold" is key. We’ve all heard about lactate threshold, the point where lactate builds up faster than it can be cleared from the blood, and how pushing this boundary can improve endurance. Your lactate threshold (LT1) is the first rise of lactate above baseline, indicating that more fast twitch fibers are kicking in. It's around 80 percent of your max heart rate and should feel like a steady, hard effort.

Why run at threshold intensity?

• Maximum mitochondrial production

• More volume without excessive fatigue

• Much more sustainable

• Recruits a high percentage of both slow and fast twitch muscle fibers without the fatigue downside of higher intensities

Double Threshold Days

This approach, championed by Marius Bakken and refined by the Norwegian endurance model, involves two high-intensity training sessions in a single day—both targeting your lactate threshold zone, typically around 2.5–3.5 mmol/L. The goal isn’t to accumulate more lactate, but to train the body to use it more efficiently as fuel.

The key to double threshold days is balance. When you train at or near lactate threshold, you're engaging the body's aerobic systems to their fullest while avoiding the rapid accumulation of lactate that leads to fatigue. By splitting two threshold sessions across a single day, you increase your time at this intensity without overstressing your body. The recovery window between sessions (usually 4-6 hours) allows lactate to clear and the body to reset, ensuring that each session is effective.

It should be emphasized that it's not about pushing your body to the well; it’s about making your body more efficient. The more often you spend time in this training zone, the better your body becomes at clearing lactate during sustained efforts. Over time, this allows athletes to hold higher intensities for longer periods.

Double threshold days allow athletes to accumulate more high-quality training without the burnout that often comes with traditional, single high-intensity sessions. While it may seem counterintuitive to train hard twice in one day, the key is that the body doesn’t accumulate excess lactate if you’ve allowed it to clear between efforts. Instead, you're enhancing your body’s ability to clear lactate more effectively and efficiently. Personally, a spin on the bike or a swim session in between my two intense runs seems to reset my body.

Bakken’s research suggests that this method boosts both aerobic capacity and lactate clearance, offering the benefits of high-intensity training while minimizing the risk of overtraining or fatigue. The result? You’re able to train hard, more frequently, and recover faster.

Double threshold days fit neatly into a larger framework of smarter endurance training. It's about training smart, not just hard. By strategically stacking two threshold sessions in one day and keeping lactate levels in check, athletes can maximize their endurance adaptations without the risk of burning out. This approach is sustainable and scientifically sound, making it a pinnacle of the more elite training that's done at Sisu Endurance Lab.