Second wind

Second wind is a phenomenon in endurance sports, such as

Documented experiences of the second wind go back at least 100 years, when it was taken to be a commonly held fact of exercise.[9] 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.^[10][11][12]

Hypotheses

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

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 cannot 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^{[clarification needed]} in Ironman Triathlon ten years ago introduced the idea of heart rate training and "tricking" one's body into staying in an aerobic metabolic state for longer periods of time. This idea is widely accepted and incorporated into many Ironman Triathlon training programs.^{[8][citation needed]}

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.^[13] Many of these proponents feel that the second wind is very closely related to—or even interchangeable with—the runner's high.^[14]

Pathology

A second wind phenomenon is also seen in some medical conditions, such as

The second wind phenomenon in GSD-V individuals can be demonstrated by measuring heart rate during a 12 Minute Walk Test.[20]^[21][22] A "third wind" phenomenon is also seen in GSD-V individuals, where after approximately 2 hours, they see a further improvement of symptoms as the body becomes even more fat adapted.^[23][24]

Without muscle glycogen, it is important to get into second wind without going too fast, too soon nor trying to push through the pain. Going too fast, too soon encourages protein metabolism over fat metabolism, and the muscle pain in this circumstance is a result of muscle damage due to a severely low ATP reservoir.^[18][19] Aiming for ATP production primarily from fat metabolism rather than protein metabolism is also why the preferred method for getting into second wind is to slowly increase speed during aerobic activity for 10 minutes, rather than to go quickly from the outset and then resting for 10 minutes before resuming.^[18] In muscle glycogenoses, second wind is achieved gradually over 6–10 minutes from the beginning of aerobic activity and individuals may struggle to get into second wind within that timeframe if they accelerate their speed too soon or if they try to push through the pain.^[18] Understanding the types of activity with which second wind can be achieved and which external factors affect it (such as walking into a headwind, walking on sand, or an icy surface), with practice while paying attention to the sensations in their muscles and using a heart rate monitor to see if their heart rate shoots up too high, individuals can learn how to get into second wind safely to the point where it becomes almost second nature (much like riding a bicycle or driving).^[18][19]

Pain killers and muscle relaxants dull the sensations in the muscles that let us know if we are going too fast, so either take them after exercise or be extra mindful about the speed if you have to take them during exercise.^[18] Otherwise, individuals might find themselves in a spiral of taking painkillers or muscle relaxants, inadvertently causing muscle damage because they can’t feel the early warning signals that their muscles are giving them, then having to take more because of the increased pain from muscle damage, then causing even more muscle damage while exercising on the increased dosage, which then causes more pain, and so on.^[18] Due to the glycolytic block, those with McArdle disease and select other muscle glycogenoses don’t produce enough lactic acid to feel the usual kind of pain that unaffected individuals do during exercise, so the phrase “no pain, no gain” should be ignored and instead muscle pain and tightness are signals to slow down or rest briefly.^[17][18][19]

Going too fast, too soon encourages protein metabolism over fat metabolism.^[18][19] Protein metabolism occurs through amino acid degradation which converts amino acids into pyruvate, the breakdown of protein to maintain the amino acid pool, the myokinase (adenylate kinase) reaction and purine nucleotide cycle.^[25] Amino acids are vital to the purine nucleotide cycle as they are precursors for purines, nucleotides, and nucleosides; as well as branch-chained amino acids are converted into glutamate and aspartate for use in the cycle (see Aspartate and glutamate synthesis). Severe breakdown of muscle leads to rhabdomyolysis and myoglobinuria. Excessive use of the myokinase reaction and purine nucleotide cycle leads to myogenic hyperuricemia.^[26]

For McArdle disease (GSD-V), regular aerobic exercise utilizing "second wind" to enable the muscles to become aerobically conditioned, as well as anaerobic exercise (strength training) that follows the activity adaptations so as not to cause muscle injury, helps to improve exercise intolerance symptoms and maintain overall health.^{[17][18][27][21]} Studies have shown that regular low-moderate aerobic exercise increases peak power output, increases peak oxygen uptake (VO_2peak), lowers heart rate, and lowers serum CK in individuals with McArdle disease.^{[27][21][28][29]}

Regardless of whether the patient experiences symptoms of muscle pain, muscle fatigue, or cramping, the phenomenon of second wind having been achieved is demonstrable by the sign of an increased heart rate dropping while maintaining the same speed on the treadmill.^[21] Inactive patients experienced second wind, demonstrated through relief of typical symptoms and the sign of an increased heart rate dropping, while performing low-moderate aerobic exercise (walking or brisk walking).^[21]

Conversely, patients that were regularly active did not experience the typical symptoms during low-moderate aerobic exercise (walking or brisk walking), but still demonstrated second wind by the sign of an increased heart rate dropping.^[21][30] For the regularly active patients, it took more strenuous exercise (very brisk walking/jogging or bicycling) for them to experience both the typical symptoms and relief thereof, along with the sign of an increased heart rate dropping, demonstrating second wind.^[21][30][19]

In young children (<10 years old) with McArdle disease (GSD-V), it may be more difficult to detect the second wind phenomenon. They may show a normal heart rate, with normal or above normal peak cardio-respiratory capacity (VO_2max).^[17][31] That said, patients with McArdle disease typically experience symptoms of exercise intolerance before the age of 10 years,^[17] with the median symptomatic age of 3 years.^[32][33]

Tarui disease (GSD-VII) patients do not experience the "second wind" phenomenon; instead are said to be "out-of-wind".^{[6][17][18][34]} However, they can achieve sub-maximal benefit from lipid metabolism of free fatty acids during aerobic activity following a warm-up.^[17]

See also

• "Hitting the wall"
• McArdle disease (GSD-V)
• Phosphoglucomutase deficiency
  (PGM1-CDG/CDG1T/GSD-XIV)
• Metabolic myopathies
• Glycogen storage disease
• Inborn errors of carbohydrate metabolism
• Tachycardia § sinus (inappropriate rapid heart rate response to exercise)
• IST § differential diagnoses (inappropriate sinus tachycardia)

External links

• IamGSD - International Association for Muscle Glycogen Storage Disease
• Training Support - IamGSD resources for "second wind", details and printouts for the 12 MWT, and physical training guidelines in McArdle disease (GSD-V)
• 12 Minute Walk Test in McArdle Disease - IamGSD Videos. A video of the 12 MWT demonstrating "second wind" using a treadmill and measuring heart rate of an individual with McArdle disease (GSD-V)

References