Speed, a crucial element in distance running, significantly impacts runners' performance. Runners who can build and maintain speed often finish ahead of their competitors. Therefore, speed work through drills, such as interval training, offers distance runners several advantages.

Engaging in speed work enables the body to tolerate and process lactate, a byproduct of aerobic cellular respiration that contributes to muscle fatigue. The heart pumps more blood to the rest of the body, allowing more oxygen to reach the muscles. When the muscles absorb more oxygen, they produce more energy.

Further, speed work allows the body to use the same amount of oxygen to run longer distances. Running fast mentally conditions runners to the stresses of distance running and positively stresses the body, making it less vulnerable to fatigue.

Runners can integrate various speed work drills into their distance training, such as interval training. In interval training, runners sprint in short spurts. For example, a runner could run as fast as possible for 400 meters and then run more slowly for 100 meters to recover.

In the Fartlek (Swedish for "speed play") workout, runners sprint for short distances. Unlike speed training, which uses distances as markers, Fartlek workouts let runners choose landmarks such as trees, road signs, or light posts as markers for running fast. Runners still run between sprints, returning to an average speed. This regimen improves endurance and helps runners become comfortable with running faster.

Stride workouts, running strides, stride-outs, and striders can also improve speed. Regardless of the name, runners accelerate, not at top speed, but faster than usual. These workouts lengthen the stride, so runners move farther without taking as many steps. Some runners stride out at the beginning of a workout in their warmup, while others wait until the end of the workout. Runners can also stride the entire run, combining strides with Fartlek drills.

Next, runners can improve their speed by running up hills. In these workouts, runners use intense effort to run up an incline of 100 to 200 meters. After running up a hill, the runner can recover by jogging or walking down. This speed drill helps runners build endurance and power in their legs.

Then, runners can build speed by improving their anaerobic threshold or converting the body from aerobic to anaerobic respiration. Aerobic respiration allows the body to use oxygen for energy, while anaerobic respiration enables the body to create energy without oxygen. Typically, this happens when a runner moves faster than the body can handle and uses up the available energy in the muscles.

Ultimately, improving this threshold allows runners to sustain speed, even if oxygen is not present in the muscle, and reduces the likelihood that the muscles will succumb to fatigue because of increased lactic acid. Lactic acid occurs when a hydrogen ion leaves lactate.

Tempo running assists runners with improving their anaerobic threshold. In tempo running, runners run slow enough to carry on a conversation. The run should feel comfortable but challenging.

Experts suggest that runners cross-train to improve their speed outside of these short drills. Cross-training allows runners to take a break from running by engaging in physical activity such as CrossFit, swimming, spinning, and soccer to improve runner speed. The exercises strengthen cardiovascular fitness while also improving range of motion and flexibility.