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So here's the story,

I went through my usual winter and early season time concentrating on building strength and endurance as opposed to shedding the typical 10-15lbs I normaly focus on prior to the start of my race season. I've had some good results so far this year, even at a heavier than normal weight. I'm now changing my long term goals to accomodate a few specific events late in the season and have started to try and drop the weight, mid season to achieve those goals.

For the past 2 1/2 weeks, I've been watching my caloric balance very closely, trying to maintain a 500-750 calorie deficit. After a week or so of this, I fould that my heart rate during rides was much higher than normal, and while my average pace has not drastically changed (though it is down), my high end speed and power is really lacking.

This is what I came up with as a possible explanation:

The negative caloric balance is depleting the glycogen storage in my muscles and liver so that even at the begining of a ride, my muscles are consuming glucose in the blood stream and nearly immediatly going anerobic as opposed to being fueled on stored glycogen. This results in faster accumulation of lactic acid. Because of the depleted glycogen stores, my bodies only way to keep up with the demands of the exercise is to increase my heart rate, to shuttle away lactic acid which is accumulating much faster than normal.

This however doesn't seem to explain my lack of top end speed. Perhaps that is a side effect of the lack of readily available fuel for the muscles? They can only put out so much based on the fuel (blood glucose which depletes quickly or fat metabolism which is not terribly efficient) present, which while trying to lose weight is scarce. By forcing my body to opperateon fat reserves am I placing a limit on what my muscles are capable of putting out?

Any thoughts? Does my interpretation seem reasonable? Also, how long would it take to replenish my glycogen stores (how long to transition out of the weight loss phase) in preparation for a race?

Thanks everyone!
 

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"The negative caloric balance is depleting the glycogen storage in my muscles and liver so that even at the begining of a ride, my muscles are consuming glucose in the blood stream and nearly immediatly going anerobic as opposed to being fueled on stored glycogen. This results in faster accumulation of lactic acid. Because of the depleted glycogen stores, my bodies only way to keep up with the demands of the exercise is to increase my heart rate, to shuttle away lactic acid which is accumulating much faster than normal."

I don't believe this is sound physiologically. Lactic acid accumulates in the blood when glycolytic rate outstrips the ability of the muscle to oxidize the products (pyruvate and maybe lactate). If glycolysis is impaired by glycogen depletion, lactic acid is less likely to accumulate.


"This however doesn't seem to explain my lack of top end speed. Perhaps that is a side effect of the lack of readily available fuel for the muscles? They can only put out so much based on the fuel (blood glucose which depletes quickly or fat metabolism which is not terribly efficient) present, which while trying to lose weight is scarce. By forcing my body to opperateon fat reserves am I placing a limit on what my muscles are capable of putting out?"

This makes more sense, fat metabolism is efficient, it just isn't fast. I'm not sure, but I would be suprised if blood glucose can be transported quickly enough into most muscle fibers to fuel glycolysis at the maximum capacity if glycogen isn't also available as a substrate.
 

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batman1425 said:
Understandable, but hindsight is always 20/20. Any potential explanation for me current situation?
How soon are your A races? Friel is saying that in a Build phase, accept your current weight and focus on training quality. The time for (substantial) weight loss is pre-season or Base phase. (The terminology comes from the Bible, if you don't have it, get it.)

The middle course would be to aim for more modest weight loss with less aggressive caloric restriction.
 

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I'm no kinda exercise physiologist, but your theory seems reasonable to me. In a very different context, I started experiencing the same symptoms. In my case, it had nothing to do (heh...)with running a caloric deficit. I was subclinically hyperthyroid from Grave's disease, and didn't know it. The only symptoms were exactly what you're experiencing, plus heat intolerance. If you have this also, get your TSH checked. If it's abnormally low (or high for that matter) follow it up. And good luck with your training regimine.
 
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