In my previous blog I introduced some of the anthropological evidence that humans are evolved for endurance running. Many in the Paleo and Primal communities believe that most of what our ancestors did was sprint and lift heavy things and very little endurance activities were employed so they tend to avoid endurance exercise. However, when you look at the adaptations that occur as a part of each exercise modality, there is the potential that combining the 2 is very beneficial through complementary adaptations.
Multiple systems are affected by resistance and endurance training. While most people only think of the adaptations that occur within the musculoskeletal system, adaptations within the cardiovascular and nervous systems are also important. Let's begin by taking a look at the adaptations to the musculoskeletal system.
As you can see, each exercise modality has differing effects on muscle cells within the body. Each tends to improve the predominant energy system it uses, phosphagen and anaerobic systems in resistance training and the aerobic system in endurance training, by improving enzymatic activities in these systems. This improves the capacity to use fat for endurance training while improving the capacity to use glucose in resistance training. A couple of the adaptations found in endurance training, increased blood flow to the muscles and increased mitochondrial density, actually see a decrease in resistance training.
This is important because increased blood flow enhances oxygen delivery to the muscles and increased mitochondrial density provides more of the organelles responsible for the use of fat as energy in the cells. Since fat requires oxygen to be burned, both are prerequisites for efficient fat burning and a decrease in either tends to hamper fat loss. Of course, since some of these adaptations work against each other from a performance perspective, a person who is training for a sport that is heavily reliant on either modality will have to fine tune the proportion of each that they do for optimal results.
From within the cardiovascular system, many of the positive adaptations attributed to exercise come from endurance training. One of these positive adaptations is a decrease in arterial stiffness which is one of the potential mechanisms that causes a decrease in blood pressure in people who regularly partake in endurance exercise(1). In resistance training, studies have shown an increase in arterial stiffness which should result in an increase in blood pressure. Interestingly enough, resistance training has also been shown to decrease blood pressure by amounts similar to endurance training, indicating that resistance training causes a decrease in blood pressure through a different mechanisms than endurance training(2). This indicates combining the two could provide better results on blood pressure than one or the other.
Another aspect of health that improves with exercise and is worth noting is the effect of exercise on the brain. Both resistance and endurance exercise have been shown to improve brain function, and studies have shown that these enhancements may be due to separate adaptations. While endurance exercise tends to increase brain-derived neurotrophic factor(BDNF) and insulin-like growth factor-1(IGF-1) in the hippocampus, resistance exercise tends to increase brain levels of IGF-1 and cause increased expression of IGF-1 receptors in the hippocampus(3). The hippocampus is a part of the brain integral to memory function and both BDNF and IGF-1 enhance it's function. For more on how this works, the book Spark by Dr. John J. Ratey covers many of the positive adaptations of exercise on brain function.
Outside of these adaptations, the general consensus in medicine is that endurance exercise helps to maintain lung and heart function throughout life while resistance training tends to help maintain muscle mass and strength(4). VO2max, a measure of cardiac output that increases with endurance training, has been shown to be a strong predictor of all-cause mortality. In other words, people with a low VO2max have an increased risk of dying from any cause compared to people with a higher VO2max(5). Muscle mass is also a strong predictor of all cause mortality; people with a higher muscle mass have a lower risk of dying from any cause than people with low muscle mass(5).
Overall, both resistance training and endurance training have benefits that are separate from and potentially complementary to one another. Adaptations to both, while sometimes conflicting, may prove to be either additive or synergistic when you combine both forms of exercise in your wellness program. Studies show combining the 2 to be superior to one or the other as a therapeutic approach to both cardiovascular disease(6) and Type 2 Diabetes(7). Whether this holds true for healthy people looking to maintain their quality of life remains to be seen, but the mechanisms for at least an additive effect are there.
In my next blog we will go over how you can apply this information to your wellness program.