PeterNem said:
How much truth is there in the stuff I keep reading which says to keep CV and weight stuff on seperate days? Is this something that only applies to people looking to seriously build muscle or does this apply to anyone? Only reason I ask is going down the gym for just 15 mins to do weights would feel a bit of a waste of the effort to get there and pay for parking etc.
Well there is a lot of truth in it. But it all depends on your goals. You will not make any significant muscle gains by doing 15 minute workouts. Since that is what you are doing I assume that lean mass gains aren't of much concern to you.
Most people recommend keeping Cardio and Resistance training seperate for two reasons.
1. Calories burned - When attempting to gain muscle you want every calorie that you consume to be expended on building muscle. By performing cardio your are taking away calories that could be used for muscle gains.
2. Intensity - When lifting weights intensity is extremely important. If you have just done a 20 minute HIIT cardio session then you are likely to be pretty tired already and thus will not get enough intensity in to your weights workout.
If you are not really trying to gain muscle then I don't see it as an issue. If you are however, then I would personally recommend you seperate your cardio and weights workouts, up your weightlifting sessions to 45 mins - 1 hour and start lifting as heavy as you possibly can. If you
have to do cardio on the same day then at least do the weights first and finish off with your cardio instead.