Your personal fitness goals may help determine whether you should perform light cardio before or after your workouts.
A light five-minute walk or cardio exercise is beneficial before any workout. The previous thought process was to stretch after a workout, and while this is still good information, research shows that performing a light cardio warm-up helps reduce the risk of injuries significantly.
If you want to increase physical fitness and gain the health benefits from regular exercise, consider performing a light cardio routine before a workout. This helps to raise the metabolism and heart rate while preparing the muscles for exertion prior to strength training.
Stick to light cardio for your warmups and cooldowns. Performing a heavy cardio workout depletes much of the glycogen stores in the muscles and reduces the amount of energy left over for strength training and can hinder that portion of your workout.
If you do both and your focus is not on bodybuilding or strength, then performing light cardio before has some benefits. Studies also suggest that this method and timing can increase the calories burned during a workout for those of us looking to shed a few pounds.
Its all About the Glycogen
When your body digests carbohydrates like pasta and breads it produces glycogen – a form of sugar. Glycogen is the primary fuel source for your muscles and they burn a lot of this during cardio or aerobic exercise.
Many endurance athletes like swimmers and marathoners are known for eating large amounts of carbohydrates before an event or workout because of the need to store up glycogen. This is where the term “carb up” comes from.
This will also be a prime consideration when planning cardiovascular exercise. If your focus is cardio health and endurance, performing cardio exercise first will be the most beneficial.
Although weight training does not burn as much glycogen as cardio or aerobics, it can still reduce those glycogen stores and energy enough to have an impact on a cardio routine. The inverse of this is also important to consider. If strength gains are your priority, it is more important or beneficial to do the strength training first and finish your workout with a light cardio routine.
The Benefits of Cardio and Strength Training
It is important to include both cardio and strength training in any workout plan. This is because your body is built up with two types of muscle fibers, fast twitch and slow twitch. Slow twitch muscle fibers fire or contract more slowly and have more endurance. These are the muscles used more predominantly in activities like running and other cardio related exercises. Fast twitch muscles are better for short bursts of strength like lifting etc. Our bodies use both types of muscle fibers and as such we need to activate and condition both through exercise.
If your workout goals are fat burning and cardiovascular health, you will also want to consider the benefits of performing light cardio before a workout. Overall, this helps to increase blood flow to the muscles during a workout and increase the fat burning effects of a workout.
Burning up the glycogen stores already in the muscles forces our bodies to rely on fat for energy. Our ancestors used energy just to hunt and gather food whereas we have food readily available. Our bodies have become very efficient at storing fat but not as efficient at burning it for energy–because energy from food is so readily available. Cardio workouts burn up energy very quickly and force our bodies into fat burning mode. This is one of the many reasons cardio workouts have been proven to be excellent for weight loss.
As we can see, if endurance or cardiovascular health is the goal of a workout routine then performing light cardio before a workout is the most beneficial. If strength training is the primary goal, performing a light cardio warm-up, about 5 minutes, is the most beneficial.
Mayo Clinic Fitness - Aerobic Excercise: How to warm up and cool down.
Mayo Clinic Fitness - Is it better to lift weights before or after an aerobic workout?
American Council on Excercise - Is it better to do my cardio workout before or after my strength training exercises?