Just what is happening in your arms as you dig deep to find the energy to put up those last two reps at the gym? No pain, no gain, has long been the mantra of exercise gurus and enthusiasts alike. But where does the pain come from?
To understand this, it is important to have a basic handle on the human energy systems. The body is a fine-tuned machine that functions on a complicated level. Some athletes train for the short run: they achieve high levels of raw power, but that power only lasts a few seconds. Other athletes train for the long run: they hit the streets and run twenty, thirty, and even in some cases, one hundred miles in a single stint. The human body utilizes two energy systems, one for short-term power, the other for long-term endurance.
SHORT TERM ENERGY Since humans have existed, they have had the need to suddenly exert forces of tremendous power, whether it is to run from a predator, to lift something heavy, or to hold on tight rather than plunging into a deep chasm. To accomplish these tasks, the body stores a ready supply of fuel that can be spent quickly. The system that accomplishes this is called the anaerobic system.
Energy comes from sugars that are taken into the body and converted to a substance called ATP. ATP is a highly efficient fuel. During the first 10 seconds of heavy exercise, such as lifting weights, the muscles burn up their ready supply of ATP. After the initial ten seconds, a second anabolic system kicks in to replenish ATP to the muscles. This process comes with a price: lactic acid buildup in the muscles. Lactic acid is thought to be the factor that causes pain in the muscles during heavy exercise and that forces the muscles to stop exerting themselves. ATP can only be generated in this manner for about two minutes of high intensity muscular activity. After two minutes, the body is forced to drop the intensity of activity and draw power from its long term energy system.
LONG-TERM ENERGY Long-term energy comes from a second system called the aerobic energy system. The muscles must have ATP in order to function. Once the anaerobic system depletes its supply of ATP, the production of fuel is taken over by the aerobic system. This system used oxygen to create ATP at a reduced rate. Enough ATP is produced to keep the body going for a long time, but not at maximal capacity. The aerobic energy system shines on long term activities like marathon running or daily functions like walking, gardening, and working.
WHERE DOES THE PAIN COME FROM? The source of soreness in the muscles comes from, first, the production of lactic acid during heavy-duty exercise. High intensity exercise also forces the muscles to exert to the point of damaging themselves. You can think of muscle fibers a long, thin wires. The damage is like breaks in the wires that cause periodic gaps. Like any injury, this muscular damage can cause discomfort or even pain at the beginning of the healing process. However, after the muscles are fully healed, they come back larger, more powerful, better able to handle the tasks that are demanded of them. It's all a part of the natural adaptation process.
So when you hear the mantra, no pain, no gain, you might translate it into the following: no expenditure of ATP at a high rate, causing muscle fibers to fire and damage themselves, no opportunity for muscles to go through a healing process that makes them stronger and better able to accomplish the tasks demanded of them.
- Craig, Nybo
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