Which is better for you to do first, cardio or workout? This is a great question and one that many people ask all the time. There are only two things that affect your workout: 1) How hard you push yourself?; and 2) How long you workout at that same intensity?
The only factor that affects both is the amount of sugar you have in your blood and tissue for your body to burn while you workout. So let's say you decide to start with a cardio workout. Many of you have probably done that. You hop on the treadmill or the elliptical and go fast or slow. Let's say you go fast to burn off some fat and get a good sweat going. Most do this with the idea that the cardio will warm the muscles up so that they will not hurt anything afterward at the weight machines when they start playing Hercules on the nautilus machines or even the free weights. Makes sense. However, many have probably found that they perform worse on the weights after the cardio than the other way around.
The logic made sense with the heat so what went wrong? The issue was never heat, it was chemistry. Muscles only perform if they have a sugar-based chemical stored in their tissues that they can draw on to push all that weight. That chemical is glycogen. Cardio burns more glycogen than pushing weight does. Therefore, the only problem with working out with weights after cardio is that it doesn't help you chemically. The cardio burns so much glycogen that very little is left for the muscles to use afterward.
Do the workout first. Your muscles will be colder, but they will have the energy they need to push the maximum weight you want to push that day. You push hard and the muscles warm as you do. You strain against the weight to build additional tissue. Then, when finished, head to the cardio with plenty of glycogen to feed the heart and legs as you run.