flapjack

I think your gym instructor is just aiming to get you toned and fit. If you want to add mass and strength you need to be doing heavy compound movements. Warm up well and do 45 minutes heavy weights then go and do some cardio, 25 minutes a session is plenty unless you are going to run a marathon. Your heart is already getting a workout from doing the weights. Train as often as you feel comfortable with. Your body will tell you if you are doing too much and you will know yourself if you are doing too little.

Just my opinion. Good Luck

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Lots of pain and some small gains