By Team ICG® Master Trainers Joan Kent and Jim Karanas

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

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

Increased Tidal Volume Improved aerobic conditioning moves more oxygen to the working muscles. The first adaptation is breathing capacity, called tidal volume. The volume of air the lungs can move with each breath increases with aerobic training due to improved diaphragm strength and breathing technique. Higher tidal volume has also been associated with longevity.

Increased Blood Volume Blood is actually an organ that responds to training by increasing in volume. With increased cardiovascular training, the body produces more red blood cells and blood to increase its oxygen-carrying capacity and oxygenate body tissues. Increased blood volume also increases the capacity to remove metabolic waste, improve recovery and sustain a greater muscle mass.

Increased Stroke Volume Stroke volume, the amount of blood ejected by the heart per beat, increases. This adaptation tends to occur at “slower” heart rates, or at least at rates less than 160 bpm. Increased stroke volume indicates improved heart function. When people talk about “strengthening” the heart, this comes the closest to being the underlying mechanism. In pumping more blood per beat, the heart moves a greater workload. The strength-training equivalent would be using a heavier weight and slow repetitions, versus pumping a lighter weight quickly.

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 a 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 an increase in both the size and density of mitochondria. Mitochondria are subcellular structures that convert fuel to energy aerobically. They are the receptor sites in muscle cells for the molecular oxygen needed to power the Krebs, or citric acid, cycle and produce ATP. Mitochondria are the only sites in the body that burn fat — with the exception of the heart, which can and will use whatever it gets, including lactate.

Increase in Type 1 Muscle Fibers* Aerobic conditioning also increases the sensitivity of working muscle to the effects of insulin, in part by promoting the development of Type 1 muscle fibers. Type 1 fibers are high-endurance fibers that respond well to insulin. (Type 2b are better for explosive power but less sensitive to insulin.) Everyone knows that 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 these conditions. (More about insulin resistance in a future post.)

Increase in Fat-Burning Enzymes This applies specifically to hormone-sensitive lipase (HSL), which moves fat from storage to bloodstream for utilization. HSL is activated when the body needs to mobilize energy stores, and responds positively to 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 development of type-1 fibers in the upper body in the same way that lower-body training affects the lower-body muscles involved.

Adaptations without an * are central adaptations that impact the entire body. Central adaptations permit a “transfer” effect, i.e., aerobic training with the upper body can improve aerobic performance using alternate muscles (in this case, the lower body). This was covered in Jim”™s post on “The Best Cross-Training for the Indoor Cyclist.”

It”™s important to address the impact of aerobic training adaptations on weight loss, because it”™s a primary goal of many who attend our classes. A distinction should be made between aerobic training and cardiovascular training generally.

In cardiovascular exercise, the heart, lungs and vessels of the body work at an accelerated rate to sustain exercise. It includes aerobic training. Aerobic training adaptations improve the body”™s ability to move oxygen to burn fuel for energy. Aerobic exercise has limited impact on weight loss because its built-in intensity ceiling becomes a limiting factor in several ways, the 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 the body”™s recovery from intense training. Trainers advocating only anaerobic work for weight loss often miss this point. Furthermore, as covered in many previous ICG® posts, training is about much more than weight loss.

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

Originally posted 2013-01-07 09:28:53.

Joan Kent

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