Aerobic Training Adaptations

The training adaptations that derive from indoor cycling are well documented and ubiquitous. Still, new instructors seem to appreciate hearing the information. Also, everyone describes the benefits a bit differently, and a change can help students understand.

So even though this is review for some, I thought a list of aerobic training adaptations, as described at ICG, would be worth covering. Some are cardiopulmonary, some vascular, some muscle-specific, or other.

Increased Tidal Volume
Aerobic conditioning moves more oxygen to the working muscles. The first adaptation is tidal volume. The volume of air the lungs move with each breath increases, due to greater diaphragm strength and improved breathing technique.

Increased Blood Volume
Blood is actually an organ that responds to training by increasing in volume. With aerobic training, the body produces more red blood cells and blood to increase its oxygen-carrying capacity and oxygenate body tissues. Increased blood volume also improves removal of metabolic waste, improves recovery, and sustains a greater muscle mass.

Increased Stroke Volume
Stroke volume, the amount of blood ejected by the heart per beat, increases. When people talk about “strengthening” the heart, this comes closest to being the underlying mechanism. In pumping more blood per beat, the heart moves a greater workload.

Enhanced Capillary Network*
Capillaries are blood vessels with walls only one cell thick. They surround the muscle cells and deliver oxygen and nutrients. The capillary network becomes denser with aerobic conditioning. This results in greater available surface area for the transfer of oxygen to the mitochondria within the muscle cell.

Increased Mitochondrial Size and Density*
Aerobic training results in larger, and more, mitochondria. Mitochondria are subcellular structures that convert fuel to energy aerobically. They are the muscle receptor sites for the molecular oxygen needed to power the Krebs, or citric acid, cycle and produce ATP. Mitochondria are the only direct fat-burning sites in the body – with the exception of the heart, which can, and will, use whatever it gets, including lactate.

Increase in Type 1 Muscle Fibers*
Aerobic conditioning sensitizes working muscle to insulin, in part by promoting Type 1 muscle fiber development. Type 1 fibers are high-endurance fibers that respond well to insulin. (Type 2b are better for explosive power but less insulin-sensitive.) Everyone knows cardio training can reduce the incidence of heart disease, hypertension, stroke, diabetes, cholesterol problems, and more. Improved insulin sensitivity is a significant mechanism in that, because insulin resistance underlies those conditions.

Increase in Fat-Burning Enzymes
Hormone-sensitive lipase (HSL), which moves fat from storage to bloodstream for utilization, is activated by catecholamines and ACTH. It’s inhibited by insulin and activated by the removal of insulin’s inhibitory effects.

Items with an * are peripheral adaptations, specific to the working muscle. Thus, upper-body cardio training, such as arm cranking, will increase mitochondria, capillarization and type-1 fiber development in the upper body the way lower-body training does in those muscles.

Adaptations without an * are central adaptations that impact the entire body. Central adaptations permit “transfer,” so upper-body aerobic training can improve aerobic performance using lower-body muscles.

In addressing aerobic adaptations and weight loss – a primary goal of many indoor cycling students – a distinction should be made between aerobic training and cardiovascular training generally.

Cardiovascular exercise makes the heart, lungs and vessels work at an accelerated rate to sustain exercise. Cardio includes aerobic training, which improves the ability to move oxygen to burn fuel for energy. Aerobic training has limited impact on weight loss. Its built-in intensity ceiling becomes a limiting factor in several ways, low calorie expenditure being only one. That’s why anaerobic training is also necessary.

A major benefit of aerobic conditioning with respect to weight loss is that it supports recovery from intense training. Trainers advocating only anaerobic work for weight loss often miss this point. Furthermore, as covered in many ICG posts, training encompasses more than weight loss.

Regardless, when it comes to the sheer pleasure of riding, indoors or out, a well-developed aerobic system lets you feel fantastic.


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