Why do you get tired?

[Neil]

Picking up on the nutrition thread...

Does anyone know the molecular basis of fatigue?

I have read that muscle fatigue is directly related to muscle glycogen depletion but I find that explanation to be a bit lame.

Like, if your gas tank is half empty your car has difficulty getting up a hill? Doesn't make sense to me.

Here's an interesting article on the subject.

 

[sardog1]

[Mini-rant coming]
I'll take this choo-choo off the main line for a short stop on a spur.

One of the several reasons that folks with packs get tired is that handy sternum strap -- many people pull it too tight. They compress their lungs just a little bit, reduce their O2 uptake, and can't figure out why they're tired right at the outset.

Give your red blood cells a chance to do their job. That sternum strap is there only to keep the shoulder straps from sliding off your shoulders. If it's not semi-loose, it's too tight.
[Mini-rant off]

 

[Chip]

I always seem to get tired come Monday morning. I'll have to do more research.

 

[smitty77]

[Mini-rant coming]
One of the several reasons that folks with packs get tired is that handy sternum strap -- many people pull it too tight.[Mini-rant off]

Makes some sense to me. I can't stand the thing, and usually leave it unbuckled. I come from the "old school" when packs didn't come with them, and am more comfortable without it. The one that I do like is on my camelback HAWG that has an elastic section, so if will flex as you breathe.

Back on the original topic... I think feeling tired has more to do with lactic acid buildup than glycogen depletion alone. Using your car analogy, I know that a motor runs just awful with a plugged exhaust, no matter how much gas you give it.

 

[TCD]

There is also accumulating damage to the muscles from micro tears; inflammation; and a host of other factors I can't think of.

The body is fabulously more complicated than an automobile, so I'm not sure if the initial analogy is valid. I think we get tired for about 50 reasons, of which probably 10 are psychological.

 

[ferrisjrf]

...I think feeling tired has more to do with lactic acid buildup than glycogen depletion alone.

I still see and hear a lot of these references to lactic acid, as the cause of muscle fatigue and soreness. This myth was dispelled years ago, but continues to persist among us weekend warriors.

A laymen's explanation, from a 2006 NYT article:

Lactic acid is actually a fuel, not a caustic waste product. Muscles make it deliberately, producing it from glucose, and they burn it to obtain energy. The reason trained athletes can perform so hard and so long is because their intense training causes their muscles to adapt so they more readily and efficiently absorb lactic acid.

Jason

 

[sierra]

[Mini-rant coming]
I'll take this choo-choo off the main line for a short stop on a spur.

One of the several reasons that folks with packs get tired is that handy sternum strap -- many people pull it too tight. They compress their lungs just a little bit, reduce their O2 uptake, and can't figure out why they're tired right at the outset.

Give your red blood cells a chance to do their job. That sternum strap is there only to keep the shoulder straps from sliding off your shoulders. If it's not semi-loose, it's too tight.
[Mini-rant off]

Ive never heard of that but it does make sense if given some thought.

 

[Neil]

One of the several reasons that folks with packs get tired is that handy sternum strap -- many people pull it too tight. They compress their lungs just a little bit, reduce their O2 uptake, and can't figure out why they're tired right at the outset.

I would have thought that by being subject to a constriction of chest expansion the body would simply increase the respiratory rate to compensate.

As far as mal-adjusted gear goes what I (very) often see is people with their poles too long. Especially on the uphills. All that energy spent lifting the arms not too mention the increased wear on the rotator cuff.

Re: lactic acid. The body mops it up very quickly. It doesn't hang around. Also, I don't think many of us would last long on a hike if we produce more lactic acid than we mop up.

The answer to my question might be in damaged or mal-functioning Calcium Channels.

 

[arm]

fatigue is under-rated ...

http://outdoors.webshots.com/photo/1200866295054138012GxZuUB

 

[Paradox]

As far as mal-adjusted gear goes what I (very) often see is people with their poles too long. Especially on the uphills. All that energy spent lifting the arms not too mention the increased wear on the rotator cuff.

I have given that some thought as far as a piece of hiking gear I have been considering. Imagine a 1 liter water bottle that you could wrap around the top part of each pole just below the handle. About half the time the weight of the water is supported by the pole and is moved forward requiring little energy from the hiker. I have been wondering if this would require less exertion than carrying the 4.4 pounds on one's back.

 

[Puck]

I still see and hear a lot of these references to lactic acid, as the cause of muscle fatigue and soreness. This myth was dispelled years ago, but continues to persist among us weekend warriors.


Jason

Lactic acid, actually Lactate, will build up during anearobic conditions...You are not getting enough O2 to the muscles cells. As the lactate gets oxygenated it is converted to pyruvate and enters the Krebs cycle.Another occurence happening as a result of anearobic conditions is the build up of acid in the muscles from the hydrolsis of ATP for energy called acidosos. ( a proton is released in the process) It is suggested that this is the real culprit.

The Ca ion pumps is interesting...perhpas the ATP is getting used for energy by the muslce cells and not going to power these pumps. The answer is to get the body in the proper conditon so that it is not operating under anerobic conditions. In the presence of O2 far more ATP is generated by elctron transport chain aka Mitchell transport chain or whatever they are calling it these days.

 

[smitty77]

Lactic acid, actually Lactate, will build up during anearobic conditions...You are not getting enough O2 to the muscles cells. As the lactate gets oxygenated it is converted to pyruvate and enters the Krebs cycle.Another occurence happening as a result of anearobic conditions is the build up of acid in the muscles from the hydrolsis of ATP for energy called acidosos. ( a proton is released in the process) It is suggested that this is the real culprit.

Sorry, a bad use of terms on my part it seems. This was more like what I was thinking of, in regards to the by-products produced in anaerobic activity. High school biology was far too long ago.

 

[Chip]

I have given that some thought as far as a piece of hiking gear I have been considering. Imagine a 1 liter water bottle that you could wrap around the top part of each pole just below the handle. About half the time the weight of the water is supported by the pole and is moved forward requiring little energy from the hiker. I have been wondering if this would require less exertion than carrying the 4.4 pounds on one's back.

(I need a "hmmm" Smiley) I would guess if the bottles were positioned lower on the poles for walking on the flats or downhill: only a bit of wrist would be needed to swing the poles forward pendulum style between grounding/resting the tips, and that might save energy. But positioned higher on the pole and hiking uphill you've got your arms lifting the weight vs your legs (you can rest step your body) and I don't think that would be more efficient. Or not. Requires testing. Good idea though.

 

[woodsxc]

I get tired because I didn't run enough in the preceding weeks.

 

[DougPaul]

I have given that some thought as far as a piece of hiking gear I have been considering. Imagine a 1 liter water bottle that you could wrap around the top part of each pole just below the handle. About half the time the weight of the water is supported by the pole and is moved forward requiring little energy from the hiker. I have been wondering if this would require less exertion than carrying the 4.4 pounds on one's back.

The energy expended accelerating and decelerating the additional mass would probably be more than the energy saved. Light weight is generally considered desirable in poles. (I also carry my duct tape (folded) in my repair kit, not wound around my poles or water bottle.)

Remember the old rule of thumb about one pound on the foot being equivalent to five on the back--your poles are your forelegs.

Doug

 

[Paradox]

The energy expended accelerating and decelerating the additional mass would probably be more than the energy saved. Light weight is generally considered desirable in poles. (I also carry my duct tape (folded) in my repair kit, not wound around my poles or water bottle.)

Remember the old rule of thumb about one pound on the foot being equivalent to five on the back--your poles are your forelegs.

Doug

I am aware that there is another school of thought about this. But then again have you tried it? It may involve some technique. i.e. learning to minimize the up and down motion of the arms. I am working on the Trailwrights List which will involve hiking several trails multiple times. It seems worth a try while wearing a heartrate monitor. At any rate it might be fun.

 

[DougPaul]

I am aware that there is another school of thought about this. But then again have you tried it?

No, but in general I prefer to carry weight in my pack rather than in my hands.

Weight on feet and perhaps also on hands does affect one's optimum cadence. For instance, my heavy winter boots slow my cadence. Increasing the cadence above the optimum increases the energy consumption.

It may involve some technique. i.e. learning to minimize the up and down motion of the arms.

I already walk funny, no point in making it worse...

Doug

 

[sardog1]

I would have thought that by being subject to a constriction of chest expansion the body would simply increase the respiratory rate to compensate.

I'm not a physiologist and I have no desire to play one either. But consider the examples of the greyhound, the saluki, and the cheetah. They all need to maximize O2 uptake for strenuous effort, albeit for a short term. If a smaller chest could be compensated for by increasing respiration rate, why have a big, deep chest filled with relatively large lungs?

In other words, big chest > big lungs > more spots on the linings of those lungs for O2 absorption. Now imagine that it takes some finite period for a lung cell to do its thing -- it surely isn't instantaneous. If I can't get the O2 to some cells because I'm constricted, there's a limit to how fast the remaining available cells can cycle, non?

OK, isn't there an exercise physiologist in this massive VFTT crowd that can help us?

 

[Hikes4fun]

http://sportsmedicine.about.com/od/anatomyandphysiology/a/musclefatigue.htm

Some interesting stuff....

 

[grog]

My chest hardly moves when I breath hard. I mostly breathe through my lower lungs, my stomach moves a lot more than my chest. If you just breathe through your chest you're wasting a lot of unused lung area.

grog