Many of the clients and athletes I train experience the following exercise phenomenon. During a moderately intense steady pace aerobic workout, they all notice the work gets easier after 15 to 25 minutes. It’s almost like a “second wind.” Physiologically speaking, what exactly is this exercise phenomenon? It was my understanding that the aerobic metabolism dominates after two or so minutes of moderately intense exercise. If this phenomenon is related to any anaerobic oxygen deficit that occurred in the first few minutes, than why does it take so long to replenish the oxygen (i.e., why not get over the hump after a few minutes?). What, if any, specific training can be performed to stop this from happening?
Prior to steady state exercise, a warm up is highly recommended for individuals due to its positive role in increasing muscle, body and blood temperature, dilating blood vessels, activating the heat dissipating mechanisms in the body, thereby improving the body’s cooling efficiency, improving range of motion around joints and increasing the activation of enzymes responsible for energy metabolism.
During this time of physical warm up, whether it is exercise specific or general, the body is consuming more oxygen. In the early stages of exercise, the oxygen uptake is below the steady-state level. This quantity of oxygen, termed oxygen deficit, is the amount of oxygen that would have been consumed if the oxygen uptake reached a steady state immediately. However, this does not happen because most individuals either do not perform a proper warm up, do not begin at a low enough intensity to allow oxygen kinetics to “warm up” or do not perform a warm up long enough. Aside from the physiological aspects, practically speaking, most individuals would benefit and may require upwards of 20 to 30 minutes of true warm up exercises at lower intensities to allow positive physiological adaptation prior to the exercise session.
Pulmonary oxygen uptake is measured at the level of the lungs during each minute of a slow warm up. Oxygen uptake rises exponentially during the first few minutes of exercise, and a plateau is achieved between the third and fourth minute. The energy provided during this early part of exercise represents non-aerobic energy or energy that is derived from the high energy phosphates that are stored plus anaerobic energy from glycolysis. After this time, the volume of oxygen consumed (VO2) continues to rise but at a slower rate during steady state exercise. This phenomenon is termed the “slow component of VO2” and includes many determinants such as cardiorespiratory work, temperature and a progressive recruitment of less efficient motor units with exercise duration.
Once steady state is reached, oxygen uptake during light and moderate exercise is similar in the trained and untrained individual. However, the more endurance trained individual will reach steady state quicker and experience a smaller oxygen deficit. In addition, the total oxygen consumed during exercise is greater for this individual, and the anaerobic component is smaller.
Therefore, to lessen the degree of oxygen deficit (and thus make the exercise seem “easier” as duration increases), it is recommended to follow a proper warm up of low intensity and longer duration than most individuals perform along with improving the cardiorespiratory system in exercising individuals through aerobic training.
- Gastin, P.B. (2001). Energy system interaction and relative contribution during maximal exercise. Sports Medicine, 31(10), 725-741.
- Lucia, A., et al. (2000). The slow component of VO2 in professional cyclists. British Journal of Sports Medicine, 34, 367-374.
- McArdle, Katch & Katch. Exercise Physiology: Energy, Nutrition and Human Performance. Fourth Edition, Williams and Wilkens, 1996.
- Tschakovsky, M.E. & Hughson, R.L. (1999). Interaction of factors determining oxygen uptake at the onset of exercise. Journal of Applied Physiology, 86(4), 1101-1113.