Anaerobic capacity refers to the maximum amount of energy your body can generate through processes that do not rely on oxygen. This ability is directly linked to your power output during high-intensity, short-duration activities, such as sprinting, jumping, or repeated high-effort bursts. Improving this capacity means you can sustain a higher level of intensity for a longer period before fatigue forces you to slow down. This capacity is highly trainable and responsive to specific protocols.
Understanding Anaerobic Metabolism
The body relies on two primary anaerobic energy systems when the demand for energy outpaces the supply of oxygen. The first is the phosphagen system, which uses stored creatine phosphate (CP) to quickly regenerate Adenosine Triphosphate (ATP), the body’s energy currency. This system is responsible for immediate, explosive movements that last up to about 10 seconds, like a single heavy lift or a sprint start.
Once the limited CP stores are depleted, the body transitions to the second system, anaerobic glycolysis, for short-term, high-power energy. Glycolysis breaks down glucose, primarily from stored muscle glycogen, into pyruvate without using oxygen. This process is faster than aerobic metabolism but less efficient, yielding fewer ATP molecules and producing lactate and hydrogen ions as byproducts. The accumulation of these hydrogen ions is what causes the familiar burning sensation and fatigue during intense efforts lasting from roughly 30 seconds up to two or three minutes.
Training Strategies for Capacity Enhancement
Training to improve anaerobic capacity requires systematically stressing these two energy systems through high-intensity interval work. The training structure must be specific to target either the immediate power of the phosphagen system or the sustained output of the glycolytic system. Training volume and frequency must also be carefully managed to allow for proper adaptation without overtraining.
Sprint Interval Training (SIT)
To enhance the immediate power of the phosphagen system, Sprint Interval Training (SIT) uses maximal, short-duration efforts. These intervals typically last between 10 and 30 seconds, demanding an all-out, 100% effort to fully deplete CP stores. Recovery periods must be long, with a work-to-rest ratio often ranging from 1:4 to 1:5, such as a 20-second sprint followed by 80 to 100 seconds of walking or complete rest. This long rest allows for nearly complete regeneration of creatine phosphate, ensuring the subsequent interval is also performed at a maximal power output. A session might involve 4 to 6 repetitions of 30-second sprints with 3 minutes of rest between each one.
High-Intensity Interval Training (HIIT)
To improve the capacity of the glycolytic system and the body’s ability to tolerate and clear metabolic byproducts, High-Intensity Interval Training (HIIT) uses longer work periods. These efforts last between 60 and 120 seconds, maintaining an intensity of 90% or more of maximum effort. The recovery intervals are shorter, often using a 1:1 or 1:2 work-to-rest ratio, which limits full recovery and forces the body to improve its lactate buffering mechanisms. For example, a session could involve 5 repetitions of a 90-second hard effort followed by 90 seconds of light active recovery.
Programming these intense workouts requires a balance, as the high demands on the central nervous system and muscles necessitate adequate rest. Most training plans recommend limiting anaerobic capacity sessions to two or three times per week on non-consecutive days. Varying the type of interval (SIT versus HIIT) allows for a more comprehensive adaptation of both the power and capacity aspects of the anaerobic system.
Supporting Adaptation with Recovery and Fueling
The true improvement in anaerobic capacity does not happen during the training session but during the recovery period that follows. This adaptation relies heavily on providing the body with the right fuel and sufficient rest. Carbohydrates are the primary fuel source for high-intensity anaerobic work, as they are stored in the muscle as glycogen and are broken down rapidly by glycolysis.
Pre-workout fueling should focus on replenishing muscle glycogen stores, which are heavily taxed by intense training. For high-volume or repeated anaerobic sessions, a daily carbohydrate intake in the range of 5 to 8 grams per kilogram of body weight is often recommended. During the training session itself, especially those lasting longer than 45 minutes, consuming a small amount of carbohydrates at a rate of about 15 grams per hour can help sustain performance.
Post-exercise, immediate carbohydrate consumption is crucial to maximize the rate of muscle glycogen replenishment. Consuming 1.0 to 1.85 grams of carbohydrate per kilogram of body weight within the first few hours post-session is ideal, as this period offers the highest rate of glycogen synthesis. This rapid refueling prepares the muscles for the next high-intensity bout, accelerating the overall training adaptation.
Beyond nutrition, physical recovery is non-negotiable for maximizing anaerobic gains and preventing injury. High-intensity anaerobic training creates significant micro-trauma to muscle fibers, which requires 48 to 72 hours for repair and supercompensation. Sleep is a major component of this process, as it is when the body releases growth hormone and testosterone, which are necessary for muscle repair and protein synthesis. Incorporating light active recovery, such as a slow walk or easy cycling, immediately after a session can also help to clear metabolic byproducts from the muscles.