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  1. #1
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    Calories per hour

    About how many calories and grams of carbohydrates per hour is optimal in a 10 hour mountain bike race? I've broken down my race nutrition plan into hour increments, I'll be using Perpetuem, Heed Gels, water and PB/Honey sandwich at 6 hours. I'm 145 pounds. With what I have available to me currently and doing some basic research, I'm thinking 58 gr of carbs, 215 calories per hour not including my breakfast (bagels and honey) and the sandwich. I think I'll take a big gulp of water every 20-30 minutes.

    Anything else I should consider? Usually I just wing it and eat what's available, but that hasn't worked out greatly in the past.

  2. #2
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    Some notes from Corey Hart, MS Exercise Physiologist at Physio Performance Lab (from testing Aerobic Assessments for athletes, aka Garmin-Cervelo Team)


    The exercise workload at which peak fat oxidation occurs is a determinant of trained status, not solely the absolute fat oxidation. An athlete with poor fat oxidation will need to focus on nutrition prior to and within training to maximize fat use during exercise and decrease reliance on carbohydrate oxidation.
    Note: To optimize carbohydrate oxidation is to simultaneously oxidize lactate (clearance).
    Note: On average, an adult has 1600 kcal of glycogen storage and can consume 320 kcal of glucose per hour of endurance activity. There exists an exercise intensity and duration at which the athlete can no longer consume sufficient glucose in addition to utilizing glycogen storage which will result in fatigue. Glycogen synthesis does not occur during exercise, therefore exogenous input from sports drinks or food must supply the liver glucose output and blood glucose levels.
    Note: In any environmental extreme (altitude, heat, humidity, and cold) carbohydrate oxidation increases for any given exercise intensity. In addition, injury or muscle soreness (i.e. within 48 hours prior intense training) may affect glycogen storage and oxidation.

    --
    In short, depends on your fitness level & pacing, but no matter who you are, 320 calories per hour (carbs) is around the maximum you can intake
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  3. #3
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    Thanks Jason.

    I'm going to try and stay in upper zone 2 for most of the race, obviously I'll hit z4 on short grunts and will be z3+ on an epic climb. At races earlier this year, Voodoo Fire and FR60, I pinned it pretty hard from the start and I wilted around mile 50 on both occasions. I'm a middle pack sport racer, so my fitness is okay. I haven't done a lot of nutrition planning in my training, but this will be a focus next season. Maybe just sticking to my plan 215+ calories per hour will tell me a lot about myself, i.e. if I bonk I obviously didn't fuel correctly. If its hotter or I decide to push it I guess I fuel more?

  4. #4
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    Quote Originally Posted by OnForm View Post
    Thanks Jason.

    I'm going to try and stay in upper zone 2 for most of the race, obviously I'll hit z4 on short grunts and will be z3+ on an epic climb. At races earlier this year, Voodoo Fire and FR60, I pinned it pretty hard from the start and I wilted around mile 50 on both occasions. I'm a middle pack sport racer, so my fitness is okay. I haven't done a lot of nutrition planning in my training, but this will be a focus next season. Maybe just sticking to my plan 215+ calories per hour will tell me a lot about myself, i.e. if I bonk I obviously didn't fuel correctly. If its hotter or I decide to push it I guess I fuel more?
    With 10 hours of racing, I'd still shoot for 300 calories per hour.
    Even an aerobically fit athlete taking in the maximum calories can run a deficit at 50% threshold around 9 hours... At 75% effort, taking in max calories will run a deficit around 6 hours.

    It all comes down to your training beforehand & fitness level, but nobody ever went wrong eating properly
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  5. #5
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    Quote Originally Posted by sprocketjockey9 View Post
    Some notes from Corey Hart, MS Exercise Physiologist at Physio Performance Lab (from testing Aerobic Assessments for athletes, aka Garmin-Cervelo Team)


    The exercise workload at which peak fat oxidation occurs is a determinant of trained status, not solely the absolute fat oxidation. An athlete with poor fat oxidation will need to focus on nutrition prior to and within training to maximize fat use during exercise and decrease reliance on carbohydrate oxidation.
    Note: To optimize carbohydrate oxidation is to simultaneously oxidize lactate (clearance).
    Note: On average, an adult has 1600 kcal of glycogen storage and can consume 320 kcal of glucose per hour of endurance activity. There exists an exercise intensity and duration at which the athlete can no longer consume sufficient glucose in addition to utilizing glycogen storage which will result in fatigue. Glycogen synthesis does not occur during exercise, therefore exogenous input from sports drinks or food must supply the liver glucose output and blood glucose levels.
    Note: In any environmental extreme (altitude, heat, humidity, and cold) carbohydrate oxidation increases for any given exercise intensity. In addition, injury or muscle soreness (i.e. within 48 hours prior intense training) may affect glycogen storage and oxidation.

    --
    In short, depends on your fitness level & pacing, but no matter who you are, 320 calories per hour (carbs) is around the maximum you can intake
    I cannot understand the point and it is not written well....

    Glycogen is not synthesised during exercise....so the nutrients must supply the liver glucose output???? and blood glucose levels ????

  6. #6
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    Quote Originally Posted by jeffscott View Post
    I cannot understand the point and it is not written well....

    Glycogen is not synthesised during exercise....so the nutrients must supply the liver glucose output???? and blood glucose levels ????
    Once you run out of the 1600 kcal your body has no more to give and you need to supply your liver/blood glucose supplies with food/sports dirnks
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  7. #7
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    Quote Originally Posted by sprocketjockey9 View Post
    Once you run out of the 1600 kcal your body has no more to give and you need to supply your liver/blood glucose supplies with food/sports dirnks
    Okay thanks...

    But this is certainly not entirely true....

    For example when one "bonks" one can continue, it is very difficult and the rate of exersion is very low....probably equal to the rate at which the liver can supply blood glucose.

    Not that bonking is going to help anyone out...

    That sugggest to me that the liver does continue to convert fat to blood sugar at some rate during exercise.

    So if on has 1600 cal of glycogen on board and can digest 320 cal/hFor a 10 hour period one would have 320*10 + 1600 cal = 4800 cal or 480 cal/h....

    I would suggest that the liver can provide an additional 200 cal/h so one has available a maximum of 680 cal/h....I believe most endurance atheletes can operate above the 500 cal/h mark.

    Interesting.

  8. #8
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    Quote Originally Posted by jeffscott View Post
    I cannot understand the point and it is not written well....

    Glycogen is not synthesised during exercise....so the nutrients must supply the liver glucose output???? and blood glucose levels ????
    Quote Originally Posted by jeffscott View Post
    Okay thanks...

    But this is certainly not entirely true....

    For example when one "bonks" one can continue, it is very difficult and the rate of exersion is very low....probably equal to the rate at which the liver can supply blood glucose.

    Not that bonking is going to help anyone out...

    That sugggest to me that the liver does continue to convert fat to blood sugar at some rate during exercise.

    So if on has 1600 cal of glycogen on board and can digest 320 cal/hFor a 10 hour period one would have 320*10 + 1600 cal = 4800 cal or 480 cal/h....

    I would suggest that the liver can provide an additional 200 cal/h so one has available a maximum of 680 cal/h....I believe most endurance atheletes can operate above the 500 cal/h mark.

    Interesting.
    Not at privy to divulge all of the information without permission; but I'll clarify. Glucose is the primary fuel for higher intensity work and is a limited resource, the faster/stronger athletes are burning fat as a fuel at a higher percentage of intensity and conserving glycogen. When you bonk you have completely depleted your glycogen stores and your fuel ratio becomes pretty much 100% fat, there is no glycogen left for the system to utilize. Depending on your fitness level & training determines your fat oxidation rate and is trainable.

    When you add fat calories (based on oxidation rate & intensity) into the equation it becomes determinable to pinpoint nearly exactly when an athlete will bonk and what intensity they can handle based on duration of event,
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  9. #9
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    sprocketjockey:
    The exercise workload at which peak fat oxidation occurs is a determinant of trained status, not solely the absolute fat oxidation.
    Is there some way to work out what my exercise workload is that provides peak fat oxidation for a set duration?
    And what is the best way to improve my ability to burn fat at high workloads.

    I do quite a few 24hr races and it seems that with the 1600kcal stored plus 300kcal an hour is around 9000kcals of sugars I can ingest, the rest I presume has to come from converting fat to energy, so it would seem if I can improve my ability to convert fat I can go faster. Or if I can train myself to still be able to convert fat while at a higher intensity I should be able to go faster.

    Any suggestions on how to do this would be great, as well as any links to articles about the above.

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    At that level of exertion, you're probably getting about 50% of your energy from fat

    from what I know, the only way to change the percentage of fat/carbohydrate usage during exercise is changing the intensity I haven't seen any proof that one can train the body to use fat more than another at the same intensity. (in people already at a high level of fitness)


    And to answer an earlier question, when the liver runs out of glycogen, it converts protein in to carbohydrate, usually from muscle.

  11. #11
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    I wish there was a magic formula, and I'm sure it can be determined for each of us -if we were hooked up to assorted machines during several varying distance races during different times of the year at differing temps, on differing courses.
    I just went through trying to manage caloric intake during a 100K race Sunday. 10,000' of climbing with >5000' in the last 15 miles. Last year's winner's GPS said 6200 calories burned in 7.5 hrs. That's right the first local pro finished in 7.5 hours. I bonked, finishing in 9 hrs.
    This year I ate more, but no more than 250 an hour. Was an hour faster but mainly by taking it slower early- maybe conserving some mojo(glycogen, muscle strength, and will) and laying it down on the climbs. It still knocked the snot out of me. (and I'm still trying to find it)

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