Cardio or Weights - Which Comes First?

We all know that both strength training and cardio each play a pivotal role in a well rounded exercise routine, but on days when you are squeezing both into the same sweat session, do you know which should come first? 

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When I was working in a gym,  this was definitely one of the more common topics of debate, which really got me thinking.  Then I started asking around my circle of friends which they thought should come first, and again, there didn't seem to be a consensus. So, I decided to do some actual research into the subject, and the answer is.....(drum-roll please).....

there is no right answer!

Ideally, strength training and cardio should be done on different days, or one in the morning, and the other at night.  This allows you to give your maximum effort to each.  However, if that's not an option, whether you do strength training or cardio first depends on your goals.

If your goal is to gain muscle mass: your best bet is to do some light* cardio prior to lifting. The reason behind this is that in order to build muscle, you want your body to go into an anabolic state, or a "rebuild/repair" state, immediately after your strength routine.  If you were to do cardio after lifting, you would be delaying this process.  Also, depending on the duration of your cardio session, your body may be forced to rely on fats and amino acids from muscle protein for energy - and if gaining muscle is your goal, you would want to preserve as much muscle protein as possible. 

If your goal is to lose body fat or maintain: cardio after strength is a-OK! After about 60 minutes of physical activity, the percentage of calories being burned from fat stores goes way up. So your body will be in "fat burning" mode during your cardio routine if it comes after an hour-long strength session.  However, keep in mind that fat doesn't allow for much intensity to be expended, so the less calories you will be able to burn during that cardio session (don't depend on the number of calories burned displayed on the machine!) 

If your goal is to increase your cardiovascular endurance: obviously cardio should come first.  If this is your goal, more than likely the strength training you are doing is mostly to maintain tone to prevent injury.  In this scenario, your cardio endurance is your number one priority, so giving it a majority of your efforts would make sense.  Just be sure you are still doing a strength routine, and not neglecting your muscles entirely. 

*Conversely,  it's not safe to do a strenuous strength workout after you’ve already tired yourself out with intense cardio...think dumbbell-meets-toe and you'll get why...

Information from the National Council of Certified Personal Trainers S.M.A.R.T. Fitness textbook as well as "Timing is Everything: Why the Duration and Order of Your Excercise Matters" found at http://www.umich.edu