In a perfect world, you would be looking for some kind of combination. They both play a huge role and I’ll explain why.

Weight lifting is actually a big one. Weight-bearing exercises, or other forms of muscle strengthening are a crucial part of any exercise regimen. Consider this: one pound of muscle requires six Calories of energy to sustain itself daily. This energy requirement is three times as demanding as fat (two Calories/day). Therefore, the more muscle you have, the more calories you can burn, which increases your ability to maintain a healthy weight.

There are other forms of muscle strengthening if you do not have access to a gym, too. Running, hiking, jumping rope, climbing stairs, using resistance bands, doing calisthenics, Pilates, and yoga are all forms of weight-bearing exercise, forcing muscles to work against gravity. This is precisely what builds muscle.

Aerobic activity is another vital component to exercising effectively. Without varying exercise often enough, muscles begin to lose some of that conditioning. So, if you are constantly doing the same thing, it is to your benefit to switch up your routine or increase the intensity (or both).

Additionally, you can switch your exercise to interval training, alternating between periods of higher intensity movements with lower intensity ones. Trying different exercise classes can also be helpful in this case.

Just as important as these first two points are flexibility and mobility. Joints and muscles should be limber and able to go through full ranges of motion pain free, but this takes some effort. Perhaps even more important, in the case of athletes and those who live active lifestyles (whether for personal or work-related reasons), it is crucial in helping prevent injuries.

Additionally, you can do weight lifting at a higher intensity, making it a type of HIIT circuit training.

The common misperception today among many people is exercise in the aerobic window, defined as activity 65-80% of the maximum heart rate (MHR), is the best way to burn fat per unit time, when this is simply not the case. Exercise at lower intensities burns a higher percentage of fat with sugar (carbohydrates) relatively, which is true.

However, exercise beyond the aerobic training zone burns more total energy (and fat) because it is at a higher intensity. On top of high-intensity exercise being more efficient in burning fat (and energy overall), there are other metabolic benefits that make this form of exercise more appealing for fat loss.

In 2009, a systematic review conducted by Melanson et al. investigated the effects of exercise on metabolic activity. The study focused mainly on moderate-intensity aerobic activities, including swimming, jogging and biking, but also including a small amount of anaerobic exercises.

The results of this study showed no discernible difference in moderate-intensity exercise’s ability to create a metabolic difference. The study also showed aerobic exercise did not provide a significant advantage to weight loss over diet by itself.

The study did show moderate exercise was helpful in maintaining weight loss, but not as effective when used at a tool to evoke fat loss on its own.

More promising studies highlighting the effects of anaerobic, high-intensity exercise regimens have begun to appear. In his book, A Primer for Exercise and Nutritional Sciences: Thermodynamics, Bioenergetics, and Metabolism, Dr. Christopher Scott of the University of Southern Maine pointed out the multiple facts in which anaerobic, high-intensity exercise benefits metabolism and the ability of the body to use calories as energy.

Before we get into his findings, it is important to understand how to account for total calories burned overall, which is broken up into three categories. They are 1) calories burned aerobically during exercise, 2) calories burned aerobically after exercise (defined as excess post-exercise oxygen consumption, or EPOC), and 3) anaerobic calories burned from exercise. EPOC is defined as the amount of energy needed to recover following exercise, regardless of the type (anaerobic or aerobic exercise). Its effects, however, vary based on the intensity of the exercises performed.

You can see here, the effects of EPOC kick in after exercise has been completed:

A 2005 study performed by Dr. Scott compared two kinds of workouts: a 3.5-minute aerobic-style workout with 3 work-equivalent 15 seconds sprints (in the anaerobic realm). This is where the effects of EPOC kick in: approximately 29 Calories were burned during the aerobic exercise and 4 were burned during the sprinting. However, when including the effects of EPOC, the total amount energy used rose to 36 Calories for the aerobic regimen and 39 Calories for the sprinting.

But it didn’t end there, when the anaerobic effects of the sprinting were also calculated for, the total energy number for the sprinting rose to 65 Calories (vs. the 39 Calories for the aerobic regimen). Thus, when accounting for the EPOC and anaerobic contributions, anaerobic exercise far outperformed the aerobic exercise in terms of calories burned.

What is even more interesting is the anaerobic exercise took a fraction of the time (45 seconds vs. 210 seconds for the aerobic exercise). Additionally, studies in 2006 and 2009 also saw similar results when comparing weight lifting as the anaerobic exercise regimen.

Looking at the caloric effect of this shift in thinking when it comes exercise is not the whole story, either. The hormonal effect of exercise is just as important. Hormonal messengers are directly responsible for signaling fat burning during exercise, and they may also play a role in EPOC as well.

Hormonal releases shift during anaerobic exercise to increase the amount of calories burned. Exercise of moderate intensity triggers the release of stress hormones, such as cortisol, epinephrine (adrenaline), and norepinephrine (noradrenaline). The release of these hormones trigger the onset of glucose metabolism, fueling the “flight or fight” sympathetic response embedded in all humans.

Increase the exercise intensity further, and the body begins to produce lactic acid, or lactate. Contrary to popular belief, lactic acid acts as a physiological buffer and signaling molecule. Some studies suggest lactate is correlated with, and may even induce, the release of testosterone and human growth hormone (HGH), two anabolic steroids.

The release of all these hormones and natural anabolic steroids work together to increase both fat loss and lean muscle production following high intensity exercise. This, over time, leads to more functionally correct movement patterns and a leaner physique.

High intensity interval training (HIIT) fits the mold as a mode of staying in the anaerobic zone of exercise. The HIIT model is based on performing high-intensity exercises, usually in a circuit or a single exercise, followed by complete rest for a short period. Those same exercises are repeated through multiple bouts until the routine is completed.

Generally, many of the workouts are much shorter in total time, lasting 25-40 minutes generally. A 2008 study explored the effects of HIIT training. The study contained three groups, consisting of 45 women 18-30 years of age, and they were divided into three groups: one was a HIIT exercises group- 20 minutes of bike sprinting for 8 seconds followed by 12 seconds of rest, the second group was within the aerobic zone of bike pedaling for 40 minutes, and the third did no exercise. The groups were tracked over 15 weeks. By the end of the trial, the group performing HIIT lost 2.5lbs of body fat, compared to 0.6lbs of fat by the sustained, aerobic exercise group. Even more astonishing is the fact the group performing HIIT workouts only took half the time!

Hope this helps!