Aerobic vs. Anaerobic Exercise:

Aerobic and anaerobic exercises are commonly referenced in endurance training and running. Aerobic and anaerobic exercises primarily differ in terms of the duration and intensity of the muscle contractions and the way energy is generated in the muscle. In general, anaerobic exercise (~80-90% MHR) relates to short bursts of high intensity exercise and aerobic exercise (~70-80% MHR) relates to low intensity exercise performed for long durations of time. Optimal results from aerobic exercise would require exercise intensity of 55-85% of MHR for anywhere between twenty and thirty minutes. While exercising in an entirely aerobic manner, the oxygen supplied to that person’s muscles is abundant enough for the muscles to supply all the energy required for the exercise. After a certain level of intensity, we may reach anaerobic exercise, as the cardiovascular system can no longer supply the muscles with oxygen quickly enough. In this situation, the muscles break down sugar into energy and result in an accumulation of lactate (a byproduct of glucose metabolism). The accumulation of lactate is what causes the burning sensation in muscle resulting from anaerobic exercise, which may eventually make it impossible to continue exercise if adequate time is not allowed for lactate accumulation to be removed from the bloodstream. For clarification, lactate is produced even at lower levels of intensity resulting from aerobic exercise.

When preparing for a long-distance event like a marathon, knowing about aerobic exercise is especially crucial. As runners train for an event, they want to optimize their pace to maintain a level of energy mainly derived from aerobic metabolism, or entering their “aerobic threshold pace,” maintaining balance between burning fat and burning carbohydrates. This pace requires a relatively low level of intensity that can usually be sustained for multiple hours. When runners improve their aerobic threshold pace, they can also sustain a faster, aerobic pace. Adapting one’s aerobic threshold pace is a large part of many programs designed to train for a marathon.

Some describe the anaerobic threshold pace as the point where glycogen, instead of oxygen, is the primary source of energy for the body. While anaerobic training will improve a person’s fitness lifestyle overall, marathon training at an anaerobic pace is not ideal because a person may not be able to sustain this intensity for an extended period of time. However, this is not to say that a person should be performing zero anaerobic training, as training at or slightly above their anaerobic threshold (the exercise intensity level at which lactic acid begins to accumulate more quickly than the body is able to remove the lactic acid from the bloodstream) may also beneficial.

The most precise way, like heart rate, to determine these thresholds is testing in a lab confirmed the most accurate way to determine anaerobic threshold (outside of blood work in a lab) is a 30-minute trial, in which heart rate is measured. For this trial, a person would run at maximum effort and take the average heart rate of the last 20 minutes of the trial to see that average heart rate for heart rate anaerobic threshold is referred to as Lactate Threshold Heart Rate (LTHR). It is important that this trial is in isolation ; if run in a group the time trial must be done for 60-min instead of a 30-minute time trial. Aerobic threshold heart rate would simply be 30-beats per minute below the heart rate determined from the anaerobic threshold trial..

In essence, threshold training is training to delay the point at which lactate begins to accumulate in the blood and, therefore, delays the point of fatigue and hopefully allows a person to run longer and faster.