Why should we lift weights if we burn more calories during an aerobic training session?

  What is Aerobic and Anaerobic training?

Aerobic and anaerobic training work differently. Each one brings different benefits.
Aerobic exercises are those activities in which the primary source of fuel is fat activated by oxygen. Those activities are characterized by keeping the heart rate from moderate to low (70% or lower).
Anaerobic or resistance exercises are those in which the primary sources of fuel is glycogen, stored in the muscles, and require no oxygen to be activated.

What is considered aerobic and what would be an anaerobic activity?

Most tasks we perform are a blend of those two types of activities. The main difference would be the proportions in which they blend. To set an example, a marathon is more aerobic than a sprint. As you have already figured out, the commonly named “aerobic” activity is something you can do for extended periods. In contrast, the frequently referred to as “anaerobic” exercise is something you won’t be able to sustain for more than a few seconds.

What activity burns more calories?

Aerobic activities burn calories while being performed, and mainly from fats. Due to the fact that we can do them for extended periods, they tend to burn more calories in a single session, but they don’t build any muscle mass or density.

Anaerobic activities burn a high number of calories while being performed (as while we sprint or do fewer repetitions with heavy-weights). Although, the total amount of calories burnt is less than with aerobic exercises since we can only perform them for very short periods. They build muscle mass, density, and strength, which also allows the body to burn more calories from fat while resting. Building muscle increases the resting metabolic rate.

What are the benefits of lifting weights?

That takes us back to the original question. Lifting weights builds muscle, elevates the metabolic rate, increases bone density and lowers the resting heart rate.
The most advisable approach is to incorporate resistance and aerobic training, to take advantage of the benefits of both activities.
The real benefits of resistance training come out of the proper technique, adequate resistance, and knowing how (and when) to increase the intensity. The correct load should be just enough to perform the exercise for 5 to 15 repetitions (typically 10 to 30 seconds), but no more or longer.