CARDIO OR WEIGHTS FIRST?
My primary goal is to increase my muscular strength, to push those last two reps where I struggle and stimulate my muscles to grow. So the last thing I need is a run that depletes my glycogen stores which is my muscles source of energy. Exercising in a glycogen-depleted state has many negative consequences, including low blood insulin and a strong perception of fatigue. This is why I warm up for five minutes only and then start training for 40 minutes. I need all my energy because I often include some jumps, runs or rowing in my workout, pursuing the goal of increasing both speed and power, which burns the hell of a lot of calories by the way. Try squatting, then leg press and add some box-jumps to the set, it’s the killer!
I do my cardio right after weights, usually half an hour interval run. Weight lifting doesn’t deplete your glycogen stores as bad as it does in cardio workouts, depending on how intense you go of course. Personally, I have always some energy left to get an alright cardio session. If you can, then divide your workout and do the cardio later. Eat something to replenish your glycogen stores and stop protein breakdown. Or even better: lift weights 4 times a week and do the running on the other two or three days. And try to schedule your run sessions as far away as possible from your kick box lesson or leg day, because running on super sore tired legs definitely sucks.
But: If you want to run a marathon or lose weight fast, you should run first. Whatever type of exercise is most important to you – do it when you are not fatigued. If you want to lose weight AND increase muscular strength, alternating the order of the workout during different cycles of training is one way to reach both goals.
And: If you have a chance to run outside, do it! It’s more fun to run in the forest with friends than to stare at a wall or TV-screen at the gym.