Second wind

Second wind is a phenomenon in distance running, such as marathons or road running (as well as other sports), whereby an athlete who is too out of breath and tired to continue suddenly finds the strength to press on at top performance with less exertion. The feeling may be similar to that of a "runner's high", the most obvious difference being that the runner's high occurs after the race is over. Some scientists believe the second wind to be a result of the body finding the proper balance of oxygen to counteract the buildup of lactic acid in the muscles. Others claim second winds are due to endorphin production, while still others believe it to be purely psychological.

Documented experiences of the second wind go back at least 100 years, when it was taken to be a commonly held fact of exercise. The phenomenon has come to be used as a metaphor for continuing on with renewed energy past the point thought to be one's prime, whether in other sports, careers, or life in general.

Metabolic switching
When non-aerobic glycogen metabolism is insufficient to meet energy demands, physiologic mechanisms utilize alternative sources of energy such as fatty acids and proteins via aerobic respiration. Second-wind phenomena in metabolic disorders such as McArdle's Disease are attributed to this metabolic switch and the same or a similar phenomenon may occur in healthy individuals (see symptoms of McArdle's).

Lactic acid
Muscular exercise as well as other cellular functions requires oxygen to produce ATP and properly function. This normal function is called aerobic metabolism and does not produce lactic acid if enough oxygen is present. During heavy exercise such as long distance running or any demanding exercise the body's need for oxygen to produce energy is higher than the supply oxygen from respiration. Anaerobic metabolism to some degree then takes places in the muscle and this less ideal energy production produces lactic acid as a metabolite. If oxygen supply is not soon restored this may lead to accumulation of lactic acid.

This is the case even without exercise in people with respiratory disease, challenged circulation of blood to parts of the body or any other situation when oxygen can not be supplied to the tissues involved.

Some people's bodies may take more time than others to be able to balance the amount of oxygen they need to counteract the lactic acid. This theory of the second wind posits that, by pushing past the point of pain and exhaustion, runners may give their systems enough time to warm up and begin to use the oxygen to its fullest potential. For this reason, well-conditioned Olympic-level runners do not generally experience a second wind (or they experience it much sooner) because their bodies are trained to perform properly from the start of the race.

The idea of "properly trained" athlete delves into the theory of how an amateur athlete can train his or her body to increase the aerobic capacity or aerobic metabolism. A big push in Ironman Triathlon ten years ago introduced the idea of heart rate training and "tricking" one's body into staying in an aerobic metobolic state for longer periods of time. This idea is widely accepted and incorporated into many Ironman Triathlon training programs.

Endorphins
Endorphins are credited as the cause of the feeling of euphoria and wellbeing found in many forms of exercise, so proponents of this theory believe that the second wind is caused by their early release. Many of these proponents feel that the second wind is very closely related to&mdash;or even interchangeable with&mdash;the runner's high.

Psychological
The second wind, like many other exercise-induced "highs", is increasingly suspected of being purely psychological; it is claimed by some to be a by-product of the confidence and pride one gains by passing one's supposed limitations. Studies have found similar results when researchers have simply offered encouragement to subjects during exercise.