Too much of any form of exercise can be bad for your body.
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Some believe that cardio or aerobic exercise is beneficial for burning fat but detrimental for building muscle. Although aerobic exercise does not build muscle to the same degree as anaerobic exercise, it does not burn muscle. Instead, aerobic training burns calories, improves endurance, reduces stress and boosts your mood, along with a host of other health benefits. Including some aerobic training is beneficial for nearly every fitness routine.
No matter what type of exercise you engage in, your body needs energy to keep you going during a workout. The aerobic energy pathway is used in traditional steady-state cardio workouts, such as jogging, walking and cycling. In the aerobic energy zone, oxygen is your primary energy source and your body doesn't need to dip into glycogen stores for immediate fuel like it does during anaerobic training.
Although your metabolism burns calories when you train, it doesn't appear to do so randomly. The majority of the calories you burn during cardio training come in the form of fat, while the rest are made up of carbohydrates. The only time your body will burn protein reserves, which make up muscle tissue, is when it has run out of fat and carbohydrate stores.
If you train too long or two often, your metabolism will break down protein, and your muscle will deteriorate as a result. Overtraining can even result in potentially-deadly conditions, such as rhabdomyolysis, which occurs when your muscle tissue breaks down to the degree that it permeates your blood stream. Smart training is finding the right balance between exercise and rest.
Building Muscle and Burning Fat
If you really want to build muscle, you need to kick off a process known as hypertrophy. This occurs when you damage the muscle cells, which triggers a rebuilding process during your recovery time. Since intense, anaerobic exercises stimulate much more muscle fiber than aerobic training, you'll gain a lot more muscle doing resistance and anaerobic training than you will with cardio. Switching between periods of high and low intensity during your training may be the ideal method for burning calories and building muscle.