<P> Anaerobic exercise is a physical exercise intense enough to cause lactate to form . It is used by athletes in non-endurance sports to promote strength, speed and power and by body builders to build muscle mass . Muscle energy systems trained using anaerobic exercise develop differently compared to aerobic exercise, leading to greater performance in short duration, high intensity activities, which last from mere seconds to up to about 2 minutes . Any activity lasting longer than about two minutes has a large aerobic metabolic component . </P> <P> Anaerobic metabolism, or anaerobic energy expenditure, is a natural part of whole - body metabolic energy expenditure . Fast twitch muscle (as compared to slow twitch muscle) operates using anaerobic metabolic systems, such that any recruitment of fast twitch muscle fibers leads to increased anaerobic energy expenditure . Intense exercise lasting upwards of about four minutes (e.g., a mile race) may still have a considerable anaerobic energy expenditure component . High - intensity interval training, although based on aerobic exercises like running, cycling and rowing, effectively becomes anaerobic when performed in excess of 90% maximum heart rate . Anaerobic energy expenditure is difficult to accurately quantify, although several reasonable methods to estimate the anaerobic component to exercise are available . </P>

What is the main product of anaerobic respiration