Alternation runs (also called oscillation runs) are designed to improve an athlete’s ability to sustain race pace by manipulating metabolic stress and recovery within the session. The primary mechanisms they target are:
By repeatedly shifting between intensities slightly above and slightly below race pace, the body becomes more efficient at sparing glycogen, delaying the onset of “hitting the wall.”
Alternating intensities trains the cardiovascular and metabolic systems to restore homeostasis even when heart rate remains elevated—an ability strongly associated with marathon performance and fatigue resistance.
Running faster than race pace recruits higher-threshold muscle fibers; running slightly slower reinforces fatigue-resistant fibers. Alternation improves the coordination and durability of both.
Although this session is particularly valuable for marathon preparation, the underlying adaptations benefit athletes training for any endurance event.
Total Long Run: Approximately 32 km
First Half: 16 km at an easy, aerobic pace
Second Half: 16 km alternating speeds every 1000 m (1 km)
During the alternating segment, the athlete switches between:
Faster than marathon pace
Slower than marathon pace
Across the 16 km alternation block, the average speed closely approximates marathon pace, but the physiological stress is significantly higher than running that pace continuously.
Running faster than marathon pace increases the rate of glycogen consumption. This creates a metabolic “threat signal,” stimulating adaptations that improve glycogen preservation and carbohydrate utilization efficiency.
Switching to a slightly slower pace does two things:
Allows partial recovery without dropping heart rate significantly
Trains the body to clear lactate and restore balance while still running
This combination develops a metabolic robustness that continuous running at steady pace cannot achieve.
If your marathon pace is 4:00 per km, then an alternation structure might look like this:
Fast 1000 m: ~3:50 per km equivalent
Slow 1000 m: ~4:15 per km equivalent
Repeat this pattern for the full 16 km alternation segment.
If you feel strong at the end, run the final 600 m at maximal controlled effort. This provides a final stimulus for lactate tolerance and neuromuscular recruitment.
Alternation runs are highly demanding and therefore do not need to be performed frequently.
One to two well-executed alternation runs during the Specific Phase are sufficient to produce significant metabolic and performance benefits.
Used appropriately, alternation runs provide a stimulus that amplifies both glycogen efficiency and high-intensity recovery—two key determinants of marathon endurance.