Over the years, we get asked by a majority of new clients whether they should get their cardio workout in before or after they do weight training. This is a highly debated topic on forums across the spectrum, from Bodybuilding websites, to weight loss websites, and military training websites. The consensus over the years has been that if you had to do both in one session that you would want to do your weight lifting first, and then follow it up with your cardio. This was because during cardio your body utilizes your glycogen stores, which will be needed for the strength workout. Another reason would be that if you are tired when it comes to lifting heavier weights, that your stability may be more compromised, lending to a sloppier workout.
A new research study out of Finland has come to conclude that if you are only working out 2-3 times a week, it might not matter.

Do you hit the treadmill before or after your workout?
A new research study out of Finland has come to conclude that if you are only working out 2-3 times a week, it might not matter. The study took 200 healthy men and women and observed them over a 24-week period where they were to perform 2-3 workouts a week. Half the group did cardio first followed by weight training, and the other half did the reverse. While the people who did cardio first initially had a longer recovery time after these workouts, over the course of the 24 weeks everything evened out, and all athletes observed a similar increase in both muscular endurance and mass.
This study did not observe athletes with a higher volume of workouts, or those with a significant workout history, so it may come to light that if you work out 4-7 days a week, the order is more significant, but if you are like most gym goers, it shouldn’t be an issue.
What does this mean to you? It means that if you have a long-term goal of getting fit and healthy, stop fretting about doing cardio or strength first, and just be sure you get them in. Both cardio and strength training are important. The better option is to split the workouts up and alternate between the workouts. This gives you the opportunity to build back up your energy stores. A third option when doing both at the same time, is to choose certain days that are cardio intensive, and other days that are strength intensive.
If you are working out more often than 3 times a week, your best bet is to observe how YOU feel after your workouts, and adjust accordingly. No advice is meant to be one-size fits all, so pay attention to how your body feels and reacts.
Source: http://www.sciencedaily.com/releases/2014/03/140313092224.htm