Second wind is a phenomenon in distance running, such as

marathon The marathon is a long-distance foot race with a distance of , usually run as a road race, but the distance can be covered on trail routes. The marathon can be completed by running or with a run/walk strategy. There are also wheelchair div ...

s or

road running Road running is the sport of running on a measured course over an established road. This differs from track and field on a regular track and cross country running over natural terrain. These events are usually classified as long-distance ac ...

(as well as other sports), whereby an athlete who is out of breath and too 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 neurobiological effects of physical exercise are numerous and involve a wide range of interrelated effects on brain structure, brain function, and cognition. A large body of research in humans has demonstrated that consistent aerobic exerci ...

", 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 Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

to counteract the buildup of

lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...

in the muscles. Others claim second winds are due to

endorphin Endorphins (contracted from endogenous morphine) are chemical signals in the brain that block the perception of pain and increase feelings of wellbeing. They are produced and stored in an area of the brain known as the pituitary gland. Hist ...

production. Heavy breathing during exercise is also to provide cooling for the body. After some time the veins and capillaries dilate and cooling takes place more through the skin, so less heavy breathing is needed. The increase in the temperature of the skin can be felt at the same time as the "second wind" takes place. 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. A second wind phenomenon is also seen in some medical conditions, such as McArdle Disease (GSD-V). Unlike non-affected individuals who have to do long-distance running, in GSD-V individuals second wind is achieved after 6-10 minutes of light-moderate aerobic activity (such as walking without an incline). In GSD-V, due to a glycolytic block, there is an energy shortage in the muscle cells after the phosphagen system has been depleted.

Exercise intolerance Exercise intolerance is a condition of inability or decreased ability to perform physical exercise at the normally expected level or duration for people of that age, size, sex, and muscle mass. It also includes experiences of unusually severe post ...

such as muscle fatigue and pain, an inappropriate rapid heart rate (

sinus tachycardia Sinus tachycardia is an elevated sinus rhythm characterized by an increase in the rate of electrical impulses arising from the sinoatrial node. In adults, sinus tachycardia is defined as a heart rate greater than 100 beats per minute (bpm). The ...

) in response to exercise, and

tachypnea Tachypnea, also spelt tachypnoea, is a respiratory rate greater than normal, resulting in abnormally rapid and shallow breathing. In adult humans at rest, any respiratory rate of 1220 per minute is considered clinically normal, with tachypnea be ...

is experienced until sufficient energy is produced via

oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine tri ...

, primarily from Free Fatty Acids. Oxidative phosphorylation is only achievable for light-moderate aerobic activity, as high-intensity (fast-paced) aerobic activity relies more on muscle glycogen (unavailable in GSD-V) and anaerobic activity causes muscles to contract which restricts blood flow (leaving oxygen and blood borne fuels unable to be delivered to muscle cells adequately for oxidative phosphorylation). The second wind phenomenon in GSD-V individuals can be demonstrated by measuring heart rate during a 12 Minute Walk Test.

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

McArdle's disease Glycogen storage disease type V (GSD5, GSD-V), also known as McArdle's disease, is a metabolic disorder, one of the metabolic myopathies, more specifically a muscle glycogen storage disease, caused by a deficiency of myophosphorylase. Its inci ...

are attributed to this metabolic switch and the same or a similar phenomenon may occur in healthy individuals (see symptoms of McArdle's disease).

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 Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

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 oxygen supplied in the blood from respiration.

Anaerobic metabolism Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing re ...

to some degree then takes place in the muscle and this less ideal energy production produces

as a waste metabolite. If the 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 Respiratory diseases, or lung diseases, are pathology, pathological conditions affecting the organs and tissues that make gas exchange difficult in Breathing, air-breathing animals. They include conditions of the respiratory tract including the t ...

, 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 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.

Endorphins

Endorphins Endorphins (contracted from endogenous morphine) are chemical signals in the brain that block the perception of pain and increase feelings of wellbeing. They are produced and stored in an area of the brain known as the pituitary gland. Hist ...

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—or even interchangeable with—the runner's high.

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