The human body fuels itself through three types of energy production methods, depending on how intense and how long you engage in that physical activity: phosphagen, anaerobic and aerobic energy production.
When energy is needed in a hurry, it's the phosphagen system that gives the body immediate energy, lasting only for seconds; ATP is able to fuel some pretty intense muscle contractions, but not for very long. Because the supply of ATP stored in the muscles is limited, the body can only sustain short bursts of energy, like sprinting for no more than five to six seconds [source: Berg]. During intense, short periods of exercise, ATP is rapidly replenished by creatine phosphate, which is stored in the body's skeletal muscles.
After that first five seconds, the rate of glycolysis — that's the process that converts glucose to pyruvate, which is needed for cellular respiration — dramatically increases by 1,000 times than while the body's at rest. The anaerobic energy system, which uses carbohydrates but no oxygen to provide for the body's energy demands, takes over [source: Stipanuk et al.]. ATP is rapidly generated during anaerobic glycolysis, to be used during intense physical activities lasting between 30 seconds and three minutes [source: Gagliardi]. If the body's demand for oxygen becomes and remains greater than what you're supplying, there is an increased risk of lactic acidosis, when pH levels decrease in the body and byproducts of the breakdown of glucose to pyruvate accumulate in the body's tissues and bloodstream.
Most of the body's energy needs, though, are produced through a process called aerobic metabolism, also known as mitochondrial respiration. During aerobic endurance exercise, oxygen is required to generate energy from carbohydrates and fats — and to keep up the production of ATP, although its synthesis is low when the aerobic metabolism has kicked in. When the measure of your oxygen consumption (V02) reaches the maximum volume of oxygen your body can use (V02max), you've arrived at your second wind. You're what some refer to as "in the zone" — you're focused, you're not in pain, and your breathing deepens to provide maximum levels of oxygen to your working muscles and maximum ATP regeneration.
As your body gets accustomed to exercising and regulating its energy needs, the odds increase that you'll see your second wind kick in more frequently because your muscles, including your heart, will be more efficient.
"I know that I'm going to have a number of highs and lows over the course of an ultra, to the extent that I don't really think of it as a 'second wind' anymore," says Rob Colenso, ultra-marathoner and RRCA-certified running coach. "It's more like, I was able to properly eat and hydrate over the last hour, and so now I feel better and have gotten a burst of energy."
Author's Note: What's happening when you get a second wind?
If and when your second wind does kick in, don't waste it. You'll feel its benefits as long as you continue to exercise that muscle or muscle group, but it comes with a caveat: Don't stop. A brief pause isn't a worry, but you'll lose it after about 30 minutes of non-intensive physical activity.
More Great Links
- Association for Glycogen Storage Disease UK (AGSD). "Second Wind -- An Essential Tool." June 1, 2012. (Aug. 18, 2015) https://www.agsd.org.uk/tabid/1386/default.aspx
- Berg, J.M. et al. "Section 30.4 Fuel Choice During Exercise Is Determined by Intensity and Duration of Activity." Biochemistry. Fifth edition. 2002. (Aug. 18, 2015) http://www.ncbi.nlm.nih.gov/books/NBK22417/
- Colenso, Robert, Jr. Ultra-marathon runner and RRCA-certified running coach. Email Q&A. Aug. 17, 2015.
- Alberts, Bruce M. John A. "Cell Biology." Encyclopedia Britannica. Aug. 27, 2014. (Aug, 18, 2015) http://www.britannica.com/science/cell-biology
- Ellington, W.R. "Evolution and Physiological Roles of Phosphagen Systems." Annual Review of Physiology. Vol. 63. Pages 289-325. 2001. (Aug. 18, 2015) http://www.ncbi.nlm.nih.gov/pubmed/11181958
- Gagliardi, Christopher. "The Three Primary Energy Pathways Explained." ACE. April 19, 2013. (Aug. 18, 2015) https://www.acefitness.org/blog/3256/the-three-primary-energy-pathways-explained
- Karp, Jason. "The Three Metabolic Energy Systems." IDEA Health & Fitness Association. Feb. 1, 2009. (Aug. 18, 2015) http://www.ideafit.com/fitness-library/the-three-metabolic-energy-systems
- Keller, B.A. "VO2 and VO2max." Medicine & Science Sports & Exercise. Vol. 23, No. S167. 1991. http://www.shapesense.com/fitness-exercise/articles/vo2-and-vo2max.aspx
- Lodish, H. et al. "Molecular Cell Biology." Fourth edition. 2000. (Aug. 18, 2015) http://www.ncbi.nlm.nih.gov/books/NBK21724/
- Peterson, Dale. "Catch a Second Wind." Wellness Clubs of America. 2006. (Aug. 18, 2015) http://www.drdalepeterson.com/Secondwind_508daf4b1839e306a3654.html
- Phillips, Casey. "Experts Say Getting Your 'Second Wind' is a Real Phenomenon." Times Free Press. April 19, 2012. (Aug 18, 2015) http://www.timesfreepress.com/news/life/entertainment/story/2012/apr/19/second-wind-101-runner-energy/75780/
- Powers, Scott K. "Exercise Physiology: Theory and Application to Fitness and Performance, 7th edition." McGraw-Hill. Oct. 30, 2009.
- Sheehan, George. "Important Running Tips For Every Runner to Know." GeorgeSheehan.com. 2013. (Aug. 18, 2015) http://www.georgesheehan.com/tips.html
- Stipanuk, Martha H. et al. "Biochemical, Physiological, and Molecular Aspects of Human Nutrition." Aug. 13, 2013. (Aug. 18, 2015) https://books.google.com/books?id=XVNPAQAAQBAJ&