Exercise and Weight Loss, Part 1: Aerobic Exercise


Aerobic/Cardio Exercise and Weight Loss

by Devin Sarno, NSCA-CPT

While most people would agree that nutrition is the true key to weight loss (or weight gain), there is no doubt that exercise has a significant affect on the process. Exercise has multiple forms, how do you know what form of exercise you should be doing to assist in your weight loss journey? Should you blend different modes of exercise? Is one better than the other? Over the next two weekends we will be covering a few different forms of exercise, specific to how they impact weight loss then you can decide what might best suit you! For the purpose of this article, we've divided exercise into four different categories to keep it concise. In this article we will focus on Cardiovascular or Aerobic modes of training and their relationship with weight loss.

Let's consider the following exercises cardiovascular or aerobic training: running (1 mile or more), biking, swimming (distance), and rowing (1,000 meters or more). Now like many forms of exercise, aerobic exercise is associated with increased energy levels, reduced stress, and improved energy health. However, cardiovascular exercise is most notably known for helping increase heart and lung efficiency and helping reduce blood pressure, resting heart rate, and risk for heart attack or stroke. It also helps increase insulin sensitivity and HDL Cholesterol, while helping reduce LDL cholesterol levels. Last but certainly not least, cardiovascular exercise promotes with weight loss.

How exactly does aerobic exercise help you lose weight? Aerobic exercise elevates and maintains your heart rate at a steadily high rate provided you are maintaining your pace throughout your workout. In doing this, it allows for you to burn a large amount of calories in a relatively short amount of time. This is going to contribute to your overall weight loss goal by helping you generate a calorie deficit. In its simplest form, weight loss is burning more calories than you consume. Obviously burning the extra calories provided by your aerobic exercise, you can create a bigger gap between the number of calories to burn and how many you consume (assuming that exercise does not cause you to eat more!). For example, say you consume the same amount of calories every day, if you introduce aerobic exercise into your daily routine and burn an extra 500 calories by going for a run, then hypothetically you should lose 1 pound a week because a deficit of 500 calories a day leads to a deficit of 3,500 calories in a week (3,500 calories = 1 pound).

The affect of aerobic exercise on the body goes deeper than contributing to your overall calorie deficit. In order to burn calories, your body needs to first utilize the nutrients you already have available to fuel the exercise. The most readily available form of fuel in your body are carbohydrates, which come in different forms within the body. Carbohydrates are stored in your muscles as glycogen and in your liver as glucose. First, your blood glucose is used as it is immediately available and can be converted to energy quickly. Then you will use up some muscle glycogen as the carbohydrate demand increases with exercise intensity. Since your body prefers carbs initially to fuel cardiovascular exercise, it makes a great tool to manage type II diabetes since it is partially caused by frequently high levels of blood glucose.
Fats are your other main source of fuel. However, they require oxygen to convert into energy making the process for them to be available for use longer than that of carbohydrates. During low intensity exercise, fats are actually the primary source of fuel since you don’t need large boosts of energy when intensity is low (i.e. walking). Even though the amount of fat being used for fuel increases with exercise intensity, the overall percentage of energy coming from stored fat is much less due to the greater energy demand, meaning a higher demand for carbohydrates. The reason this point is important is because most cardiovascular exercise (running, biking, swimming, rowing) is going to be classified as high intensity. Therefore, you will have a high demand for carbohydrates throughout the course of this mode of exercise and use them up quickly. 

Once your carbohydrate levels are depleted, your body does not just automatically start using its stored fat for energy. Protein can actually be converted to glucose and can be a backup energy source when carbohydrates are not as available. The problem with this scenario is that protein is needed to build and maintain lean muscle mass and for recovery. If your body resorts to using protein as an alternative energy source, it can inhibit recovery and potentially have a negative affect on maintaining your lean muscle mass. Lean muscle mass is important for increasing your resting metabolic rate which will lead to burning more calories throughout your entire day. So consider the following carefully when incorporating cardiovascular exercise into your weight loss journey: carbohydrate consumption before and after your exercise and exercise duration and intensity.

Aerobic or cardiovascular exercise is probably the least intimidating form of exercise and the most common for people looking to lose weight or get in shape. As far as weight loss is concerned, aerobic forms of exercise are great at burning a high amount of calories in a short amount of time and contributing to your overall calorie deficit. And don't forget the multitude of benefits for helping manage or reduce the risk of high blood pressure, diabetes, stroke, or heart attack; all of which are often associated with obesity or being overweight. One drawback is that it is not an ideal mode of exercise in regards to building or maintaining lean muscle mass, which is important to having a higher resting metabolic rate and burning more calories at rest throughout your day. That's where strength training comes in so check back tomorrow where we will cover our second exercise category: Strength Training!