Anaerobic Exercise: What It Is and How to See It in Your Training Log

Anaerobic exercise breaks down glucose in the body without using oxygen. In practical terms, anaerobic exercise is more intense but shorter in duration than aerobic exercise. When you look at your own workouts, this means your hardest, shortest efforts are where anaerobic energy systems contribute the most.

What “anaerobic” really means

The term anaerobic literally means "without oxygen". Anaerobic exercise breaks down glucose in the body without using oxygen.

Glycolysis is the biochemical process in anaerobic exercise that converts glucose to adenosine triphosphate (ATP). Anaerobic glycolysis exclusively uses glucose and glycogen as fuel when ATP is needed faster than aerobic metabolism can provide. The rapid breakdown of glucose during anaerobic glycolysis results in formation of lactic acid, which exists mainly as lactate at biological pH. Anaerobic exercise leads to a buildup of lactic acid.

Fast twitch muscles operate using anaerobic metabolic systems. When your training log includes efforts that feel explosive and powerful, those efforts are where fast twitch muscle fibers and anaerobic metabolism are heavily involved.

Anaerobic vs aerobic exercise in practice

Anaerobic exercise is more intense but shorter in duration than aerobic exercise in practical terms. Aerobic exercise includes lower-intensity activities performed for longer periods, such as walking, jogging, rowing, and cycling.

Physical activities up to about thirty seconds rely primarily on the ATP–CP phosphagen (alactic) system. Beyond about thirty seconds, both aerobic and anaerobic glycolysis-based metabolic systems are used. Intense exercise lasting upwards of four minutes may still have considerable anaerobic energy expenditure.

For sports that require repeated short bursts, the aerobic system acts to replenish and store energy during recovery periods to fuel the next burst. Training strategies for many sports demand development of both aerobic and anaerobic systems.

Anaerobic exercise may be used to help build endurance, muscle strength, and power. Benefits of adding anaerobic exercise include improving cardiovascular endurance, building and maintaining muscle strength, and losing weight. When you review your own records, sessions that feel hardest and shortest are candidates for the parts of your plan that target these anaerobic-related goals.

The two anaerobic energy systems

The anaerobic energy systems include an alactic system, based on high energy phosphates ATP and creatine phosphate, and a lactic system, based on anaerobic glycolysis.

The alactic ATP–CP system

High energy phosphates are stored in limited quantities within muscle cells. Physical activities up to about thirty seconds rely primarily on the ATP–CP phosphagen (alactic) system.

When you look back at your workout log, you can mark any all-out efforts that lasted up to about thirty seconds as efforts where this ATP–CP system was the primary anaerobic contributor, using this duration guideline as your label.

The lactic (anaerobic glycolysis) system

Anaerobic glycolysis exclusively uses glucose and glycogen as fuel when ATP is needed faster than aerobic metabolism can provide. The rapid breakdown of glucose during anaerobic glycolysis results in formation of lactic acid, or lactate at biological pH.

Beyond about thirty seconds, both aerobic and anaerobic glycolysis-based metabolic systems are used. Intense exercise lasting upwards of four minutes may still have considerable anaerobic energy expenditure. You can use these time ranges to annotate interval sets in your notes as involving both aerobic and anaerobic glycolysis when they extend beyond about thirty seconds at high effort.

Lactate, fatigue, and what your muscles are telling you

Lactate has traditionally been thought to be detrimental to muscle function, but this is likely only when lactate levels are very high. Elevated muscle and blood lactate concentrations are a natural consequence of any physical exertion. Anaerobic exercise leads to a buildup of lactic acid.

Muscular fatigue depends on many factors besides lactate, including energy availability, oxygen delivery, perception of pain, and psychological factors. When you log a workout, adding short notes about how much energy you felt you had, how your breathing felt, and how your mood or motivation felt can help you match your subjective fatigue to these different factors over time.

Measuring and training your anaerobic side

Anaerobic energy expenditure is difficult to accurately quantify. Some methods to estimate the anaerobic component of exercise include determining the maximum accumulated oxygen deficit or measuring lactic acid formation in muscle mass. These methods show that truly precise numbers usually require laboratory-style measurements, so your everyday records will mostly rely on duration and intensity as practical clues.

High-intensity interval training (HIIT) is an exercise strategy performed under anaerobic conditions at intensities that can exceed 90% of maximum heart rate.

The effectiveness of anaerobic activity can be improved through training. Anaerobic exercise also increases an individual's basal metabolic rate (BMR). Over weeks and months, noting which workouts you intend as anaerobic sessions can help you see how often you are giving yourself chances to adapt in these areas.

Training strategies for many sports demand development of both aerobic and anaerobic systems. When you step back and look at your calendar, you can mark which days emphasize longer, lower-intensity aerobic work and which days emphasize shorter, higher-intensity anaerobic efforts, so that both systems appear in your plan.

How to audit your own records for anaerobic work

To connect these concepts to your actual data, you can run a simple audit of your workout records.

• First, scan your recent workouts and highlight any all-out efforts that lasted up to about thirty seconds, and label them as relying primarily on the ATP–CP phosphagen (alactic) system using the time guideline from the source.
• Next, find intervals and efforts that lasted longer than about thirty seconds at high intensity, and mark them as efforts that used both aerobic and anaerobic glycolysis-based systems, again following the duration statement from the source.
• Finally, add a brief note to a few intense sessions about perceived fatigue, including energy, breathing, pain, and psychological factors, using the list of fatigue contributors from the source as a checklist.

Try this audit once for the last two to four weeks of training, and notice how clearly you can now see where anaerobic exercise shows up in your own log and how consistently you are training these energy systems.

This article is general health information and is not a substitute for medical diagnosis or treatment. Consult a healthcare professional if you have concerns.