Mach42

This is a pretty basic physiology question, but I tend to tire quickly when I'm on rides where I'm pushing. My legs are burning and feel lethargic during the ends of my rides, but I'm not out of breath at all and I'm not struggling with heart rate. When I'm starting off and fresh, I can push my heart rate to the limit.

I did a century last year and started off way too strong trying to keep up with the group. After about 50 miles I was pretty beat and the above symptoms reared their ugly heads, and hard. The last 50 miles were a major struggle.

Can someone tell me the basics of what's happening as I get tired? Is it glycogen depletion? Running out of matches?

bac

The simple answer is that you need to build up more endurance. Do longer training rides, and keep a log to keep on track. Your performance in the late stages of a ride will improve for sure.

... Brad

Zephyr11

Sounds like lactic acid buildup in your muscles. Work to increase your lactate threshold.

Carbonfiberboy 

What do you mean? When I think of struggling with HR late in a ride, I mean that I can't get it to go up anymore, which is a result of my legs and whole aerobic system getting tired. High HR late in a ride is great. Your equipment will only work hard for so long. How long depends on your base, in terms of miles/week and miles/month and miles/year. More miles = longer before you're out of gas.

You may very well be running out of glycogen. That's common with riders who try to go hard on a much longer ride than they're used to. I see it every Sunday. You can combat it by eating more during the ride - trying for that 250 cal/hr, steady. And riding more.

What happens with more training is that your body's chemical factory becomes more adept at using fat and food calories for energy, and gets much better at sparing the glycogen.

ericgu

It's simple. You're just pushing too hard for your level of fitness.

Mach42

This winter hit me pretty hard, and due to classes and fun new video games, I didn't get out there nearly as much as I should have. I'm fairly detrained compared to the end of last fall because of all that.

As for my heart rate, yes, I am having trouble reaching a high heart rate at the end of my rides. My legs are so dead that I cannot push at all. My heart rate and breathing are just plodding along at a very low rate and my legs die before I can really push enough to bring my HR and breathing up.

It looks like a long hard road back, but I'll get return to where I was. Thanks for the replies, everyone.

Richard Cranium

There are no "basics" to answer with.

In general, sensations of fatigue are rooted in a complex mix of psychological and physical sensations. Often there is a tendency to draw conclusions from a single stimulus, such as exercise, or a given blood-sugar concentration and automatically declare that factor as the cause for "crashing."

As far as a direct physiological cause, the act of simply starting a ride with more highly trained athletes "sets you up" for discomfort and or fatigue in as much as you are calling on organ systems at intensity levels that release neurologically active substances that increase your awareness of work. Training can affect some of these things, but has no effect on others. (We are not machines!)

Typically glycogen depletion isn't the direct cause of "feelings" of fatigue. Many other chemical "warning-signals" , in conjunction with low-blood pressure, and low blood-glucose, and a changes in electrolyte balances all conspire to cause "crashing."

127.0.0.1

yeah you are out of something...shape. just ride more and worry less.

CbadRider

+1 The burning feeling is the buildup of lactic acid that your body can't filter out. Instead of pushing hard all the time, focus on increasing your LT.

Mach42

I've got a great "shape," just not the fitness to go along with it anymore . I have noticed that I'm nowhere near as good as the beginning of the 2008 season. That winter, I did a hell of a lot of trainer work during the off season and felt great during the spring. However, I do get the picture. I'm just doing some whining and realizing that I need to get the heck out there and work for it. I'm just saddened by the fact that I'm nowhere near in condition to ride the century that some of my friends are going to do.

daxr

You're probably on the right track thinking about glycogen depletion, though exhaustion can come in different ways. I haven't ever tracked heart rates so I don't know about that, but as far as cycling distances I'd say if you are doing one "distance ride" a week and trying to get to the century mark comfortably, just do it by adding 20% or so to whatever last week's ride was, and match the effort level.

That is, if you rode an easy 50 miles last week, make this week an easy 60 miles, then next week an easy 72 miles or so. At that point if you don't have enough time for longer rides, make them harder rides instead. For most people a 1 week recovery period between distance work is ok, and actively doing other kinds of riding in between helps too.