This made me LOL. AoE's answer hit the nail on the head - doing endurance training and expecting to build muscle simultaneously is unrealistic. If you don't want to lose or gain weight, do nothing - training for fintess will most likely affect you one way other the other! You need to impart focus to your training: if building muscle is a priority, then you should consider weight training first and foremost; if stamina/endurance is a priority, then cardio should be your first consideration - regular swimming, running, cycling, sport etc. You can't set goals without having direction to begin with. Decide what sort of physique or type of fitness you require, and work forward from there.
Definitely this started doing ju jitsu when i got to uni and we usually do some boxing at the end and I'm far fitter than i was at school when i did athletics and ran twelve miles a week.
I seem to remember that doing strength circuits provides fairly balanced improvements in both muscle mass and endurance. Is that not the case?
I do circuit training 3 times a week. It's great for overall fitness (muscle and endurance). I also find training in a class with others more motivating meaning that I gain more.
Eat sensibly. Get plenty of the goods food in you if you want to build muscle. Get plenty of fish and lean meats in you for protein and brown rice, pasta are great for carbs! I'd say 45mins free weights and 10-15 mins cardio ie running, or steps machine!
i didn't think fish was very good for you any more, i do take fish oils you know high strength seven seas. Don't like pasta or brown rice I do cardio with weights for an hour an half including running stairs and weights and supplying exercises for a couple of hours, of course on different days but all in total 2 days on 1 day off and repeat. works for me