The Ultimate Endurance Middle Ground
The Half Marathon (13.1 miles or 21.0975 kilometers) has exploded in popularity to become the most favored long-distance race in the world. It provides the grueling, rewarding challenge of endurance running without the brutal, months-long recovery required by a full marathon.
However, pacing a Half Marathon is notoriously difficult. It is too long to sprint like a 5K, but too short to jog comfortably like a Sunday long run. You must hold your body precisely at its lactate threshold for nearly two hours.
Predicting the Pain Cave
To find your perfect race pace, coaches rely on prediction models based on your recent performance in shorter races (like a 5K or 10K). The most accurate and universally adopted model is Pete Riegel's formula.
The Formula
Riegel's formula mathematically calculates exactly how much your pace will naturally degrade as you double or triple the distance you are used to running.
The Strategy of the Half
If your prediction calculator tells you that your potential finish time is 1 hour and 45 minutes, that dictates a strict 8:00 min/mile pace.
- Miles 1-3 (The Trap): Adrenaline will make 8:00 feel incredibly slow. You must actively restrain yourself from running 7:30 miles, or you will flood your legs with lactic acid.
- Miles 4-10 (The Grind): You lock into the 8:00 pace. It will feel progressively harder.
- Miles 11-13.1 (The Finish): This is where the prediction is tested. If you paced correctly, you will have just enough glycogen left to hold on or even slightly accelerate to the finish line.