Warming up the muscles you are about to use is very important, more than you would think. It helps prevent injuries to the body part you are working out. But even more important you get rid of the waste that has been built up in your muscles and new fresh blood saturated in oxygen is now coming in.
Also, probably the most important part, you can train more intensely after you warm up. The muscles can contract harder and therefore you can get a better workout.
The most common and probably most effective way to warm up is by doing the same exercise with light weight and a lot of reps, around 12. Stretching should be a part of your warm up, stretch each muscle you are about to use for at least 8 seconds.
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Also, probably the most important part, you can train more intensely after you warm up. The muscles can contract harder and therefore you can get a better workout.
The most common and probably most effective way to warm up is by doing the same exercise with light weight and a lot of reps, around 12. Stretching should be a part of your warm up, stretch each muscle you are about to use for at least 8 seconds.
Source: