Run Slow to Go Fast

Most people start running by going out a few times a week and pushing themselves as hard as they can for a mile or two. While this might feel productive, it’s not the most effective way to build endurance. The key to long-term success is to run slow to go fast. About 80% of training should be done at a low to moderate effort, where you can comfortably hold a conversation—also known as Zone 2 training.

Training in this lower intensity zone allows your heart to adapt in ways that make running easier over time. The left ventricle of the heart gradually expands, increasing stroke volume—the amount of blood pumped with each beat. This means your heart can circulate more oxygen-rich blood to working muscles without needing to beat as fast. Over time, your resting heart rate drops, and your heart becomes more efficient, allowing you to sustain effort for longer and at faster speeds.

At the same time, metabolic adaptations are happening at the cellular level. When training at a slower, controlled pace, your body becomes better at utilizing fat as a fuel source, sparing glycogen stores and reducing the likelihood of hitting a wall during longer efforts. Mitochondria, the energy-producing structures in cells, increase in both number and efficiency, improving your ability to generate sustained energy. This leads to steadier energy levels and better endurance over time.

In contrast, constantly pushing yourself at high intensities forces your body to rely primarily on glycogen, leading to quicker depletion and fatigue. It also produces more lactate, which, without a well-developed aerobic base, can accumulate faster than your body can clear it, causing that heavy-legged, burning sensation. While fast running has its place, relying on it too much without building a strong aerobic foundation can lead to slower recovery, increased fatigue, and a higher risk of burnout. Many runners say they feel like they have “more energy” over time, and that’s not just a feeling—it’s a physiological reality. By training at lower intensities, your body becomes more efficient at producing and using energy, making running feel easier and more sustainable in the long run. 

Running is also a skill, and like any skill, your body adapts to make it as efficient as possible. Over time, your movement patterns adjust to minimize energy expenditure, which is generally a good thing. However, if you have muscle imbalances or weaknesses, your body may adapt in ways that compensate for those weaknesses, potentially leading to inefficient or injury-prone running mechanics. This is why strength training plays an essential role in improving running performance. Strengthening key muscles, especially in the hips, glutes, calves and core, helps maintain proper running form, absorb impact, and reduce the risk of overuse injuries.

This increased efficiency doesn’t just help with endurance—it also lays the foundation for speed. By spending most of your training time at a lower intensity, you build a strong aerobic base, which allows you to handle harder efforts when it’s time to push the pace. Without this base, high-intensity work can be more taxing, leading to burnout, slower recovery, and a greater risk of injury. But when you’ve developed the necessary cardiovascular and muscular endurance, your body is more prepared to handle sprints, intervals, and race-pace efforts without breaking down.

As you become fitter, your "slow" pace will naturally get faster. What once felt like an easy effort will start to feel even easier, and your body will be able to sustain a quicker pace at the same level of effort. The best runners in the world still do most of their training at an easy pace, but their easy pace is much faster than the average runner’s. That’s the power of building a strong aerobic foundation. Over time, your endurance improves, your efficiency increases, and your definition of “slow” evolves. Slow for me 6 months ago was 11 minutes per mile with occasional walk breaks to stay in zone 2, today I run my easy zone 2 runs at about 9 minutes per mile. 

Stay Healthy,

Thomas Stevens