# Help me understand more about heart rate training



## mm9 (Jul 20, 2009)

As some of you suggested, I'm reading some research papers and books. Whew, some of this stuff is tough to get my head around. Trying to simplify and clarify some things in my mind - are my simplified statements correct?:

1) So, in base level mileage, the primary fuel is fat, correct?

2) One the goals of a lot of base training is to improve the efficiency of using fat as a source of fuel because it lasts longer than glycogen stores so that you can save your glycogen for later in the ride or the race, correct? 

3) Another key goal of base training is to raise the level of power output (which translates into being faster) over time within the fat burning zone. By increasing the amount of sustained power that an athlete can produce within the fat burning zone, helps the Athlete go longer and to save more glycogen for the end of the ride or at other points in the ride when a burst (glycogen fuel) may be needed - correct?.

4) Part of this low base process creates more cell mitochondria and other changes that improve things at a cellular level which help this aerobic performance?

5) A smaller but important % of training should be dedicated to pure Anaerobic (glycogen burning) training and ability to quickly recover. This allows for more power capacity and more sustained effort in this zone when the race or ride ramps up. Correct?

6) Work in the Anerobic realm has also been shown to be an efficient way time wise to improve overall VO2 uptake.?

7) The current thinking in the literature seems to be that we should spend less time in the middle category (the threshold between fat burning and glycogen burning). This one is a little more confusing to me, but I think the advice here is that it doesn't prepare the rider very efficiently for raising performance in the fat burning zone, nor does it do as good of job in the glycogen burning zone. So even though a good bit spirited group ride or race may be near the threshold, we can get more training efficiency by expanding our capabilities in the fat burning zone and the glycogen burning zone. Do I have this correct? I'd like a little more explanation on this logic if anyone understands it.

Thanks for your thoughts.


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## ibericb (Oct 28, 2014)

You're pretty close. The one place you appear to stumble is in your association of glycogen with anaerobic metabolism.

At very low levels of intensity your body will use plasma and muscle stores of triglycerides (fatty acids) as fuel to drive ATP synthesis. Because of the energy density (9 kcal/g), and the fact that they can be stored without water, they are very efficient stores of energy. Triglyceride stores in the body provide enough fuel to continue effort for many hours. However, because of the metabolic pathway they can be processed only relatively slowly. A good description of fatty acid metabolism, and it's role in endurance performance, can be found here.

As intensity increases your body needs energy to drive ATP synthesis faster than fatty acid metabolism alone can provide. It then turns to using glucose and glycogen via aerobic metabolism. The issues are (1) the rate at which glucose or glycogen can be metabolized., and (2) the limited availability of useful glucose and glycogen stores. That will typically limit the effort to an hour or two before those stores become exhausted, and the familiar bonk sets in.

With aerobic respiration comes lactic acid production. However, at low rates of production, it can be further processed as fuel so it doesn't really accumulate, but levels will rise as intensity increases leading to the familiar burn with harder effort.

If the effort is raised even more you may reach a point where energy is needed even faster than aerobic metabolism can provide. Without oxygen, anaerobic metabolism can supply more enrgy. but your body can only drive ATP synthesis for a few minutes via that pathway, and with that comes with a flood of lactic acid production that occurs faster than it can be processed, so it accumulates rapidly.

It's important to bear in mind that there are crossovers in the relative amounts of energy being supplied by any pathway at a given moment. It is never pure on or the other. The recruitment of differing numbers and types of muscle fibers is dictated by effort and power needed, and that in turns determines the varying degrees of different pathways being utilized at any moment. Training is used to develop and promote those different pathways, and just as there are crossovers in the relative amounts of any pathway, there are crossovers in the benefits derived from emphasizing one pathway that can be utilized in other pathways.

A few resources that may help a bit:
1. A simple overview explanation about different energy pathways used during exercise or demanding physical activity.
2. Presentation on Exercise Metabolism by Brian Barr, Univ of SC.
3. Physiology of Nutrition Lecture series from UCLA - see Lecture 6.
function to respiration process.

You can also find a number of insightful articles on training & performance, as well as nutrition at the Gatorade Sports Science Institute site. Browse around a bit - a lot of good stuff.


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## ibericb (Oct 28, 2014)

A delayed addition - a couple of additional references I didn't have readily marked and had to re-find.

1. A good overview description of the three metabolic pathways used by muscles.

2. A good series of blog posts by James Hewitt - a former pro cyclist, cycling coach, and sports scientist. It includes entries on lactate and polarized training. Like Friel, he leans towards timing training around event demands, and doesn't believe that polarization alone is the best approach for every cyclist, depending upon experience and event type.


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## mm9 (Jul 20, 2009)

Ibericb: Thanks for the great references. Very interesting and detailed info.


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