Exercise Physiology I: Cells and Organs

This lecture shared quite a lot of content with some of the lectures in PHYL3001 and BIOC3004. Hopefully that means that this post will be easy to write!

Describe and understand the three systems used to replenish ATP in muscle contraction
Describe and understand the physiological differences between these three systems, and how that affects performance

See earlier post: Exercise Metabolism

Phosphocreatine (PCr), mentioned in the above post, is also known as creatine phosphate (CP). Together, CP and ATP make up the "phosphagen" system. Dephosphorylation of creatine phosphate via creatine kinase (yeah, its name doesn't really make sense in this context, but I think it's a reversible enzyme) can produce energy by itself, or it can donate its phosphate group to ADP to regenerate ATP.

Describe and understand the role of muscle glycogen in endurance exercise and its effect on fatigue
Describe and understand the physiological basis of carbo-loading

Glycogen is one of the main ways in which muscles store energy. Glycogen can be broken down into glucose via glycogen phosphorylase, which in turn is activated by Ca²⁺ influx. In addition to glycogen, muscles also have a store of triglycerides, and can obtain even more fuel from passing blood.

During exercise, muscle glycogen is the first fuel to be used. Over time, fatty acids and glucose are taken up in order to continue to supply the muscle with energy. Once glycogen stores are depleted, however, exhaustion occurs and further exercise becomes impossible. Increasing glycogen stores by increasing the amount of carbohydrate in the diet may help in increasing the time for fatigue to set in. Therefore, a lot of endurance athletes will participate in "carbo-loading"- increasing their glycogen stores so that they will have more stamina.

High carbohydrate diets will also assist in replenishing glycogen after exercise. Interestingly, not eating will replenish a little bit of glycogen too (around as much as for a fat and protein diet following exercise). This may be due to the breakdown of muscle.

Describe and understand the morphology and physiology of the different muscle fibre types

Another topic that I mentioned in my good ol' post about exercise metabolism!

Now for some stuff that I didn't mention in that post:

• The types are distinguished based on their isoform of myosin ATPase
• Type I fibres have a lower calcium-handling capacity than type II fibres
• Type I fibres have a higher capillary density and mitochondrial volume than type II fibres

Describe and understand the recruitment of the different fibre types during exercise of different intensity

As exercise intensity increases, more fibres are recruited. At low intensity, only type I fibres are needed, but as intensity increases, type IIa and IIb fibres join in on the action.

Describe and understand how differences in fibre type makeup affect exercise performance between individuals

I thought I'd mentioned this before, but apparently not. Sprinters and other athletes involved in short, highly-intense activity tend to have a higher proportion of type II fibres. Endurance athletes, on the other hand, tend to have a higher proportion of type I fibres. The next question is whether people become a certain type of athlete because their fibre type proportions are more suitable, or whether they have a certain fibre type proportion because of their training (i.e. is it nature or nurture)?

Describe and understand what is VO2 max
Describe how training changes VO2 max
Describe and understand the potential morphological and physiological limits to VO2 max

I don't think VO2 max was even mentioned in this lecture (there are two slides, but I don't think he actually talked about them at all), but I have talked about it briefly in a previous post: Exercise Metabolism. (Yep, it's that post again.) As VO2 max is a measure of the maximum capacity to take up and use oxygen, I would assume that all of the systems that are involved in oxygen transport and uptake could represent limits to VO2 max. For example, the ability of the circulatory system to transport blood, and the amount of mitochondria able to take up and use oxygen, could both limit VO2 max.