As a 27 year fitness industry veteran I have seen many changes to our understanding of the benefits of strength training versus aerobic aka cardiovascular conditioning. For many years we were taught that the key to fitness was steady state aerobic training because it was understood that this type of training optimized the use of fat as energy during exercise. While this is undoubtedly true there is a lot more to the story!
The confusion comes because we need to look at two different aspects of exercise – what is happening during exercise and how the body responds after exercise during recovery from exercise. The way to look at this is that exercise is a stimulus and stressor designed to produce an adaptive response from the body. In fact the cardinal rule of exercise physiology is the S.A.I.D. principle which is Specific Adaptation to Imposed Demand. Simply put exercise = demand and the body adapts to the type of demand/exercise specifically. So long distance runners look very different from powerlifters because the imposed demand of long distance running is very different than that of powerlifting.
So if we start with the end in mind we have to define the end goal and then understand how different types of exercise demand create different short and long term adaptive responses in the body. So let’s take a look at the difference in how the body responds to steady aerobic exercise demands (such as running or cycling at a steady pace) versus resistance training such as lifting a weight to muscular fatigue for all the major muscle groups of the body.
In aerobic exercise we are placing relatively low demands on many muscles in the body for a long period of time. During exercise this allows the body to use more fat as a fuel compared to glucose/sugar. In fact the higher the intensity of exercise the less fat you can use for fuel as a percentage of total calories being used. Conversely the lower the intensity of exercise the more fat you can use as a percentage of total calories used. On the surface it would seem that if you want to get rid of fat the key is aerobic exercise, but remember there are two parts to exercise: the response during exercise and the adaptive response after exercise.
In addition, at the end of the day fat is like the body’s energy savings account while glucose/sugar is the checking account and they are linked accounts. When you overdraw from the sugar account/checking account you pull energy from fat account automatically (the savings account). So at the end of the day just like two bank accounts it is all about the total dollars/energy you pull out and put in during a given time period and where the energy comes from during exercise is NOT the key factor. So you can do a higher intensity exercise which uses no fat whatsoever but uses more total energy/calories and end up with more fat loss than exercise at a lower intensity which uses 100% fat for fuel during exercise.
Also as alluded to above the adaptive response to aerobic exercise is very different than the adaptive response to strength training. The body adapts to aerobic exercise by optimizing the generation of energy from aerobic pathways and favors a shift in muscle fiber types away from fast-twitch muscle fibers which only use sugar for energy to slow-twitch endurance fibers which use fat for fuel. Again on the surface this would seem to favor aerobic exercise for fat loss, but we have to consider what are goals are. Consider the appearance of high level endurance athletes and contrast that with high level sprinters who spend quite a bit of time lifting weights. Who would you rather look like?
The body adapts to resistance training exercise very differently than aerobic exercise demands. Strength training demands a lot from muscles with high levels of tension for much shorter period of times and little to no fat is used during the exercise as stated above. However, AFTER exercise that all changes. After strength training, particularly high intensity strength training, the body works to repair damage to muscles and build more muscle tissue to be prepared for the next strength training session. This process is called muscular hypertrophy and requires significant energy which has to come from somewhere (remember that ultimately if we take in less energy from food and beverages than we use the energy ultimately ALWAYS come from fat stores!).
Strength training favors the maintenance and development of more of the body's fast twitch muscle fibers and there tends to be more of a shift away from slow-twitch endurance muscle fibers because endurance is not what is being stressed during the workouts.
So long story short including a high intensity strength training exercise component in your workouts is key to reducing bodyfat and achieving a toned, muscular appearance. There are many effective high intensity strength training protocols and you do not have to lift very heavy weights or do higher risk strength training exercises to get the benefits of strength training.
If you are not familiar with how to do strength training correctly it is really important to work with a personal trainer for 5 – 10 sessions to learn how to lifts weights with correct form so you get the most from your workouts.