What happens in the body during interval training
Interval training is a form of exercise where periods of high intensity are alternated with short recovery periods or lower intensity activity. This training method is widely used to improve cardiovascular fitness, oxygen uptake, and endurance performance. During interval training, several physiological systems work together to supply energy to the working muscles.
When exercise intensity increases rapidly, the body must quickly adapt in order to produce sufficient energy. This involves increased activity in the cardiovascular system, the respiratory system, and the body’s energy metabolism.
Increased oxygen uptake
During high intensity activity, the body’s demand for oxygen rises significantly. Oxygen is used within cells to produce energy through aerobic metabolism. To meet this demand, both ventilation in the lungs and the transport of oxygen in the blood increase.
Several physiological responses occur.
• breathing rate increases
• ventilation volume in the lungs increases
• oxygen uptake in the blood rises
• more oxygen is transported to the muscles
These adaptations allow the body to maintain a high rate of energy production during intense exercise.
Activation of energy systems
Interval training activates several energy systems at the same time. At the beginning of a high intensity interval, the body primarily relies on the phosphocreatine system and anaerobic glycolysis to rapidly produce energy.
As the effort continues, aerobic energy production contributes more to ATP generation.
During interval exercise several processes occur.
• rapid breakdown of phosphocreatine
• increased anaerobic glycolysis
• increased ATP production
• increased aerobic energy metabolism
This combination makes interval training particularly effective for developing multiple energy systems simultaneously.
Heart and circulation
The heart plays a central role in transporting oxygen and nutrients to working muscles. During interval training both heart rate and stroke volume increase in order to meet the elevated energy demand.
This results in several physiological responses.
• increased heart rate
• increased stroke volume
• increased cardiac output
• increased blood flow to working muscles
These responses allow greater delivery of oxygen to the muscles during intense exercise.
Lactate production
At very high exercise intensities, the energy demand can exceed the body’s capacity to produce energy aerobically. When this happens, anaerobic glycolysis increases and lactate production rises.
Lactate production is a normal part of energy metabolism during intense exercise.
This may lead to several physiological effects.
• increased lactate concentration in the blood
• increased acidity within muscles
• increased ventilation
• greater perception of effort
Interval training can improve the body’s ability to tolerate and clear lactate during intense activity.
Long term training adaptations
Regular interval training can lead to several physiological adaptations in the body. These adaptations can improve both endurance and overall exercise performance.
Possible adaptations include.
• increased maximal oxygen uptake
• improved capillary density in muscles
• increased mitochondrial density
• more efficient energy production
These changes allow the body to work more efficiently at higher intensities over time.
Summary
During interval training multiple energy systems are activated simultaneously. The heart, lungs, and muscles work together to supply energy to the working tissues. Over time this type of training can produce significant physiological adaptations that improve cardiovascular fitness and physical performance.
Sources
Laursen, P. B., & Jenkins, D. G. (2002). The scientific basis for high intensity interval training. Sports Medicine, 32(1), 53–73.
Buchheit, M., & Laursen, P. B. (2013). High intensity interval training: Physiological responses and adaptations. Sports Medicine, 43(5), 313–338.
Midgley, A. W., McNaughton, L. R., & Jones, A. M. (2007). Training to enhance the physiological determinants of long distance running performance. Sports Medicine, 37(10), 857–880.
