Which type of energy-producing system you use during your workout is largely dependent on your heart rate. Anaerobic exercises bypass oxygen as a primary energy source and use glucose instead. A drawback of intense anaerobic exercise is its effect on your heart rate. The harder you work, the faster your heart beats, which can be dangerous, especially for those who aren't in good condition or have a history of heart problems.
A byproduct of the consumption of glucose as a primary energy source is lactic acid. Lactic acid buildups increase the acidity in muscle cells and disrupt metabolites. Effectively, the more lactic acid you build up through continuous anaerobic exercise, the more you limit the capacity for your muscles to perform work. Typically, the average person can only sustain anaerobic energy production efficiently for one to three minutes.
Just because your body breaks down carbohydrates for energy during anaerobic exercise doesn't mean oxygen uptake decreases. In fact, since you can only keep up anaerobic activity for a few minutes at a time, your cardiovascular system plays catch-up trying to replenish your muscles with oxygen. The longer you keep up your exercise, the more oxygen your body demands, but it eventually gets to a tipping point where you can't take in enough oxygen to meet these energy demands.
Anaerobic exercise is beneficial for building muscle and increasing overall fitness, but it's also stressful and damaging to muscles in the short term. After an intense anaerobic workout, you need time off from training to rest and recover so your muscles can repair themselves properly. Delayed-onset muscle soreness usually reaches its peak one to three days after a hard workout.