(Original post by Classical Liberal)
You seem to think cardio does hurts muscle development? It does not. Cardio just uses energy. Which means it increases your required calorie intake to maintain fat. And if you do not take in enough calories, then your body will use its fat stores as a substitute (that is what fat is for, muscle is not designed to be used for energy). It is only once you get down to really low body fat levels, such as close to starvation, will the body start to use muscle for energy.
So when somebody tells you that you are burning muscle, just ignore them.
You seem to want to gain muscle and get a six pack (good call). The best thing to do to get a six pack is to get your body fat % down. This means you have to run a calorie deficit. Which means not gorging yourself on food and doing plenty of cardio. Having strong abs is largely irrelevant. You just need to get rid of the fat covering your abs.
Gaining muscle whilst running a calorie deficit is perfectly possible (despite what some rugby players will tell you). You just need to eat enough proteins and vitamins to have the building blocks for creating muscle. This approach does mean you have to tailor your diet to make sure you get enough protein and vitamins. So that means substituting fatty crap with fruits, nuts, eggs, etc.
I am sure people are going to start saying I am talking ****, and that you have to bulk and cut, but you simply don't. As far as I am concerned, such an approach is an excuse to be a greedy ****er whilst pretending you are doing it for fitness (very common among so called rugby players in my experience). If all you cared about was muscle gain, then yes eat **** loads and get fat whilst you do it. However if you want to gain muscle whilst losing body fat, you have to run a calorie deficit and you have to eat enough proteins and vitamins to rebuild your muscle. This will probably lower the amount of muscle you gain ( slightly compared to eating loads) however your overall fitness and how you look will be much better.
When you are building muscle the process works roughly like this. You workout. You "break" the tiny fibers in your muscles. The body then repairs these fibers and makes them bigger than before. To do this the body need the necessary building blocks for muscles. Which are amino acids and energy, I think. The amino acids will come from eating proteins and vitamins you consume. And the energy will come from the calories you take in, or your fat stores. Now assuming you have some fat on your body, the chances of you running out of energy for this process are slim to none (which is where this *******s idea that cardio harms muscle development comes from because you use up energy during cardio). On the other hand if you do not have enough protiens and vitamins, your body will not be able to repair the broken fibers and you will end up weaker than before because you have literally damaged your muscles and no allowed to repair (this is a real danger of happening in practice, as opposed to the fear of running out of energy).
This process of repairing damaged fibers takes around 3 days I believe. You need to keep your body full of proteins and vitamins during this time. This means taking on said ingredients regularly and in small doses, as opposed to having one massive protein shake after your workout, which is absolutely pointless.
Also, once you have damaged your fibers, do not workout that muscle again for atleast 3 days. You need to give the body time to repair the muscle. Otherwise you can end up just stopping the whole rebuilding process by continually damaging your fibers. This is why I think it is a good idea to work out muscle groups on different days, to make sure you do not overtrain and muscle group.