Steady state 📈O2 model

ndurance physical activities are limited by the capacity of the respiratory and circulatory system to deliver oxygen to the working muscles. Such activities are classified as "cardio-respiratory" or "aerobic" endurance activities (11). The degree to which the system limits one's performance is based on various factors such as the intensity of the exercise, duration of the activity, and the amount of activated muscle contraction involved. These areas of limitation may be modeled to provide information for future adaptation responses and identifying areas of risk. In general, low-intensity and long-duration activities such as distance running or cycling have reduced activated muscle contraction and are generally limited by oxygen (O2) utilization capacity. On the other hand, high-intensity and short-duration activities such as weight lifting require large amounts of activated muscle contraction. These activities are classified as "anaerobic" activities allowing for energy production outside cellular mitochondria (11). However, there are activities such as soccer and basketball that may fall in between the classified aerobic and anaerobic activities. The energy required for such activity comes from a combination of aerobic and anaerobic sources. It could thus be argued that all endurance activities use and transition between both aerobic and anaerobic components of energy production (3,9). Researchers have investigated the role of O, uptake kinetics during exercise (1). Astorino et al. (1) studied the kinetics of O2 uptake in the transition to exercise and found that the VO, measured in the transition to exercise near or above peak VOr would be slower than those for subventilatory threshold exercise. Moreover, several studies have demonstrated that a physiological measurement such as maximal oxygen uptake (Vomax) is a useful predictor of success in endurance