Will cardio make you burn muscle?

There's a lot of speculation about this, and in some cases (when cardio isn't done correctly) It will make you burn muscle. However, it's not as easy as some people seem to think to burn muscle, your body is efficient, it was made to survive and doing a little cardio here and there will not make you burn muscle. In fact, it may do quite the opposite. 


When does cardio make you burn muscle OR prevent you from building it?

Cardio can be a wide variety of things, low intensity, high intensity, interval training, circuits etc. You can't really say that one type of cardio will have the same effect as the other. It's all dependent on what you're doing and for how long you're doing it. For instance, if you're trying to gain muscle and you're doing high intensity cardio sessions every day for about 30 minutes and you're wondering why you're not improving..well that's your answer. You're simply putting too much stress on the central nervous system. Hindering recovery and growth. You may want to minimize the intensity of your cardio, or the frequency. Another problem may be, you're doing say a fasted cardio session in the morning and maybe hitting the gym for weights at night. If you're feeling tired and weak when you're doing weights, or you simply cannot lift what you're used to and not giving it your all you may be inducing muscle loss. Why? because when you're not providing that stimulus, that requirement of maximal effort, your muscles don't need to adapt to your training and you won't grow. 

Food. The big one. So, it's well known that to grow you want to be in a calorie surplus to really reap the benefits. Cardio, is a calorie burner. (of course depending on what you're doing) so if you're burning too many calories then you're not going to grow! You need to be taking into account the fact that you're doing this extra exercise and account for it in your diet. Keep your protein high, if you're doing cardio and burning these fuels your body simply does not have the raw materials to synthesize muscle tissue. 


When does cardio help you gain muscle?

Cardio can improve muscle recovery; it increases blood flow to the muscle tissues for repair. Light cardio can also stimulate appetite, thus potentially allowing someone who finds it hard to hit their daily macros on a 'bulk' to eat a bit more. It may also improve insulin sensitivity, meaning that the body is more efficient in the muscle synthesis and less prone to storing fat. (WIN WIN) Another factor is just general health, by cutting out cardio completely you're just not going to be as fit and healthy. Health is important and is often put aside in bodybuilding. So cardio shouldn't just be for cutting in my opinion, a little cardio here and there whilst bulking is a good thing, it also makes the transition from bulking to cutting a lot easier when it comes down to it. Effectively, or in my opinion..the right cardio can turn your body into a machine. Whereby it metabolizes food in the best way possible and promotes muscle growth. 


What approach should you take?


The balance between gaining muscle and losing it is different for everyone. Some people may be able to do more cardio and have a better result from it, others not so much. You should know yourself what works for you. Can you give your weights sessions your all? do you feel strong? are gaining at all? If the answer is yes, then you're doing it right. If you enjoy cardio, you don't need to give it up because 'cardio ruins gains' you just need to know what is an optimal amount for YOU. Just be sure you're eating enough, you're not overtraining and you've chosen a frequency/duration and intensity that suits you. 

If you're a hard gainer, avoid high intensity cardio. If you're prone to gaining fat and muscle relatively easily, you could add a HIIT session into your routine and still reap the benefits of your weight training. Play about with it, and see what works for you as an individual.