I know there are different types of muscles: fast twitch and slow twitch. Everyone has a mixture of both, those with fast twitch muscles can sprint best, those with slow twitch muscles can jog for longer.
But on further research, scientists found that the difference was only about 40/60 in the most extreme cases and that is just not enough to justify saying "I cannot do a certain exercise, its not possible". It is possible to train for anything if you a) put in the effort and b) really want it to work.
I am not the biggest fan of exercising- I hate it. It leaves me sweat, feeling out of breath and my muscles ache. But I still force myself to do so. I prefer other forms of exercise such as core stability, abs, yoga...but if I just did those exercises I'd not be challenging myself. I may find myself able to do a handstand with dramatic ease, but I'd not have great fitness in my mind- I'd only be able to do one sort of thing.
Exercise works well when its varied. Variation helps stop you becoming bored bt also means your body has to work harder- it has more to learn, more to recover from, can do more as a result and can train harder. As a result you get a better looking physique as its not so easy to overlook certain muscle groups or over work others.
See, there really is little excuse- you can really do anything bar physical issues getting in the way.
If your chest pains become too bad, see a doctor, get heart issues ruled out but I can say for the most part, its likely to be a sign that your pushing yourself outside your comfort zone and this is a good thing in terms of improving your fitness.
See it works like this: you exercise and your heart pumps blood fast around your body (circulation.) It carried oxygen in the blood to feed the muscles and this oxygen means they can carry on working. Where does the oxygen come from? its from your lungs. Your lungs and heart need to work harder in order to pump oxygen around your body when you exercise and if your not used to it, it may feel difficult and take some practice to get better at it.
Your going to notice a difference in your breathing, it becoming more laboured as your lungs and heart work harder. It wont always be like this.
Things which can make things harder are;
Being a smoker or even a heavy passive smoker (the lungs are put under more pressure and its harder to get oxygen to circulate around the body as a result).
Being overweight (the heart has to work that bit harder as fat builds up around the heart).
Being tierd or stressed or malnourished: the organs are tierd and the same force to work hard is not there, they need to rest so they can work properly.