Cardio before or after strength training? Different people will tell you different things but let’s look at what SCIENCE has to say. The body first uses ATP and CP(Creatine Phosphate) energy systems when lifting, which gives you an instant boost. Once that’s out, it moves on to using glycogen stores in the bloodstream for energy, and finally, it gets to burning fat. This means that you are able to strength train more intensely and with more energy because you are using the 2 most efficient energy sources available to the human body. Once those are depleted, it’s actually good to go to cardio, since at this point you’ve already burned past your initial energy sources and can quickly jump into fat burning using the third and last system the body has to produce energy which is the oxidative system.