Athletes usually increase anaerobic endurance by purposefully exercising at or near the anaerobic threshold. This is usually accomplished by way of interval training, wherein an athlete performs a series of high intensity activities interspersed with recovery periods at a lower intensity. This training regimen typically increases the anaerobic threshold, which is directly related to anaerobic endurance. Interval training is usually sport-specific, so runners typically perform a series of hill runs or track sprints, cyclists perform speed intervals, and so on.
Anaerobic exercise uses energy stores within the muscle cells to power physical activity. The cardiovascular system is normally unable to keep up with the demands of the working muscles, so most of the energy metabolism powering the cell is performed in the absence of oxygen. During the process, lactic acid is produced as a byproduct, accumulating on the cell and lowering the pH and, in turn, the efficiency of energy production. When lactic acid concentration reaches a critical point, the muscle cells are no longer able to produce enough energy to contract, resulting in muscle failure. This point is called the anaerobic threshold.
Interval training promotes anaerobic endurance by increasing muscular stores of adenosine triphospahte, glycogen, and phosphocreatine, each of which is involved in anaerobic metabolism. Additionally, muscle cells adapt to interval training by increasing buffering capacity, which enhances the cell's ability to manage lactic acid. These adaptations increase the muscle's ability to work at a high intensity for an extended period of time.
Exercise intensity can be determined by monitoring heart rate. Maximum heart rate is calculated by subtracting the athlete's age from 220. Target intensity is then expressed as a percentage of the maximum heart rate. Anaerobic training typically requires working at an intensity of about 80 to 90% of this number, and interval training to increase anaerobic endurance usually involves the higher end of this range.
To add interval training to a workout, an athlete should begin by performing a light warm-up of 10 to 15 minutes, to increase blood flow to the involved muscles. The first high-intensity interval should last about one minute, and be followed by a cool-down period wherein the heart rate falls to 120 beats per minute or lower. A full workout will normally include about six intervals, adjusting as needed, depending on personal preferences and fitness levels. As anaerobic endurance increases, the muscles will become more efficient at coping with lactic acid, and less time will be needed for recovery.
Runners use a variation on standard interval training to increase anaerobic endurance, speed, and power. Fartlek training involves random intervals, usually while running on a path or roadway. The interval begins when the mood hits, ends when the runner is sufficiently exhausted, and training continues for as long or as short a period as is desired. Fartlek training is often praised as being more fun and spontaneous than standard interval training, and is especially enjoyable when performed with a running partner.