Dont worry most people feel this way. In fact its totally normal.
When you start a short burst of intensive exercise such as Kettlebell swings, snatches, sprints, rowing etc you are exercising anaerobically for approximately 3-4 minutes. Anaerobic respiration is a term that describes our bodies state when we are exercising without oxygen. When we stop exercising or moving our respiratory system then has to repay that oxygen this is know as the Oxygen Dept.
An example of this is when you start your snatch test of 100 snatches in 5min. The first 20 snatches seem pretty comfortable, right? This is the point when you are working anaerobically. At this point your respiratory system starts to catch up with the demands of the effort and stress put on the body. After a few more reps you start to feel that your movement becomes slower and slightly harder. This is when we get that feeling of wanting to give up.
Never give up! If you keep pushing on and use the correct breathing pattern you will eventually meet the oxygen demands that the body needs and start to feel relatively comfortable. This will help you get those valuable last few reps out to complete the snatch test or your chosen workout. Similarly, if you have ever gone for a run the first few hundred metres are always the hardest, but if you persevere you start to get into that “cruising” state and can manage the demands.
Once you have finished your snatches or swings beautifully (with technique that I would be proud of!) the oxygen required by the respiratory system and what you actually managed to take in during your workout is known as the Oxygen Deficit.
This Oxygen Deficit will have to be repaid at the end of the workout. This is why you will breath heavily at the end of a short period of exercise.
So after exercise there are other factors causing an increase in oxygen needs as well as repaying the lack of oxygen during exercise.
The chart below is often seen and shows how the amount of oxygen used by the body changes over time. At the beginning the body works anaerobically leaving an oxygen deficit. Over time the oxygen consumption levels out to a steady state. After exercise the oxygen is pain back (oxygen debt). Notice the area of oxygen debt is greater than the area of oxygen deficit for the reasons stated above.
Lactic acid is a by product of exercising without using oxygen (anaerobially). It is essential this is removed but it is not necessarily a waste product. It is recycled into other useful chemicals: