When it comes to weight loss, I recommend doing cardio first. Cardio exercise is going to help you burn the most calories in the shortest period of time. Although weight training is also going to help with weight loss (and should be part of any workout routine), I would make cardio the activity you're going to do while you have the most energy and your muscles are rested. No matter which order you choose, the second activity is going to suffer (to a certain extent) because you've already used up some of your energy. If you can do your cardio and strength training on different days, that would be the ideal situation. But no matter which order you use, you'll want to do a good 5-10 minute warm up before each workout session.
Nicole Nichols, Certified Fitness Instructor
What I always say matters most is that you're actually doing both cardio and strength training—in any order, on any days, at any time—and continuing to push a little harder to become even more fit. While I do agree with the perspective that it’s ideal to do cardio and strength training on separate days for optimal results, most people’s schedules don’t allow that. If you have to do both in one day, your second best option is to do them at different times of day—such as cardio in the morning and strength training in the afternoon or evening. This two-a-day approach gives you time to rest and refuel enough that you’ll have optimal energy once again by the time you get to your second workout.
But exercising twice in one day isn’t feasible for most busy people. If you have to fit in both during one workout, you should focus on whichever exercises will help you reach your main goals, and do those first. Perform cardio first if you want to lose weight, train for an endurance event, or achieve the general health benefits of exercise. Do strength first if you want to build size and power. Be sure to eat something within two hours of starting your workout session and within about one hour of completing it. Keep the length of your combination session reasonable and realistic so that you have enough energy for each part of your workout.
Personally, I do a little bit of everything—cardio first on some days, strength training first on others, cardio and strength on separate days, and even two separate workouts in one day. I like the variety, but also enjoy the mental and physical break that comes when I can focus on just one thing at a time. Changing the timing and order of your exercise program is yet another way to keep your body surprised, stave off boredom, and maximize your results.