The difference between strength training and cardio and how often to do each type of exercise is often unclear in fitness. Most people know strength training helps build muscle and cardio helps burn fat, but there is more to it. Both strength training and cardio have different pathways to turn chemical energy in the form of ATP into movement.
When doing cardio (such as running, swimming, or biking), the body gets its ATP from oxidative phosphorylation which is a process that begins with breaking down glucose (carbs) or fats through glycolysis and fatty acid oxidation. Oxygen is required, so this is described as aerobic exercise. This pathway is much slower and happens at lower intensity than strength training.
In contrast, during strength training (such as weight lifting), the body uses the phosphagen system to generate large amounts of energy in short periods of time. This system remakes ATP quickly through transferring a phosphate from creatine phosphate to ADP; this requires no oxygen, and thus it is called anaerobic. There is a limited supply of creatine phosphate, and so the body can only sustain high intensity bursts for usually less than 30 seconds.
Strength training between 30 seconds and 3 minutes uses another anaerobic process of breaking down glucose into pyruvate to be put into lactic acid cycle to quickly make ATP rather than oxidative phosphorylation.
Cardio is better for faster weight loss because it burns more calories during a workout than strength training. However, because strength training builds muscle, it is beneficial for fat loss and a more efficient metabolism in the long term. After a strength training workout, the body continues to burn calories because there is excess post-exercise oxygen consumption. With consistent strength training, an extra three pounds of muscles can increase basal metabolic rate (the rate at which your body uses energy) by 120 calories.
Additional health benefits are pertinent to each. Strength training protects the body from injury and increases bone strength. As opposed to strength training, cardio increases longevity, creates a healthier heart and lungs, decreases inflammation, improves cholesterol, lowers blood pressure, and amplifies endurance.
Depending on your ultimate goal, you can incorporate more of one or the other, but it is important to have a balance of both in your workouts because they complement each other.
Doing strength training every day without a proper plan and proper nutrition puts an excessive amount of stress on the body. Similarly, too much cardio can actually cause the body to initiate compensatory mechanisms that increase fat gain and inhibit muscle building.
To make the best of both worlds, try HIIT workouts, which are aerobic workouts that integrate intervals of anaerobic. This type of training increases endurance as well as builds muscle. You can find plans for strength training on the OrgSync page of the Be Well Health and Fitness student club.