Pump and Burn in Weight Training

group of people in plank position doing rows with dumbells
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The "pump" and the "burn" are common lingo in the gym among weight trainers and bodybuilders. Here's what is happening and what it means for your training. When you train hard in the gym, especially when you train to failure, you will notice two things:

  • The Burn: Burning sensation in your muscles during exercise.
  • The Pump: Swelling of the muscles during and after exercise.

Muscle Burn

Muscle burn comes first, in a sense, because it is the first thing you feel when you are at your limit of the repetitions and/or weight you can lift. High repetitions at a lower weight will also cause the burn. The burning sensation is caused when your muscles enter anaerobic territory.

Anaerobic Training

Anaerobic means "without oxygen," but in exercise physiology, it really means that your oxygen intake and supply cannot meet the demands of your muscles. In this anaerobic scenario, acid conditions and the production of hydrogen ions build and you get the burning feeling when the nerve cells and receptors are impacted.

In years gone by the burning sensation was thought to be caused by lactic acid/lactate, which is produced under these conditions. But we know now that lactate is probably a helper response, an attempt by the body to remove these hydrogen ions.

Training helps your muscles deal with this acidic environment and athletes who must compete in this anaerobic state need to train in that environment as well. Muscle builders and bodybuilders utilize the burn in order to enhance muscle development. Lactic or at least acidic metabolic conditions seem to assist the growth of muscle.

Myths about the burn include that it is related to burning fat. This is not the source of the sensation, and in fact, fat is not being burned in the anaerobic glycolytic phase, the body is only burning glycogen.

Exercising until you feel the burn is not a foolproof way of determining if the exercise is effective. The weakest muscles will be the first to produce the burning sensation.

The Pump

Following a weight training session, you may notice a feeling of "fullness" in the muscles. This is not quite swelling, which implies a medical condition, but definitely a feeling of increased size, which is also visually noticeable. This is "the pump."

The pump is caused by blood plasma getting trapped in the spaces between muscle cells through the action of muscle contraction. It lasts about 30 minutes after your session is complete. Bodybuilders will use it to sharpen up definition just before going on stage to be judged.

This does not seem to have any adverse health effects; however, you do need to maintain adequate glycogen (glucose) stores and be well hydrated to ensure a good pump. Low-carb diets will not be a good approach. If you want to show off your guns, you might use the pump to boost them to a higher caliber.

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  • Cairns, SP. "Lactic acid and exercise performance: culprit or friend?" Sports Medicine 2006:36(4): 279-91

By Paul Rogers
Paul Rogers is a personal trainer with experience in a wide range of sports, including track, triathlon, marathon, hockey, tennis, and baseball.