Oct 2014
9:27am, 28 Oct 2014
1,110 posts
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Canute
Rosehip I am afraid my main reason for being happy about being able to fuel my running with fat is not because it will help me lose weight. Maybe losing a few pounds would be helpful, but I will only achieve weight loss if I do not replace the burned fat with food intake – whether in the form of carbs, fat or protein. That is not my main goal at present.
The reason why it is important for a marathon runner to increase the ability to burn fat is complex, but it is worth discussing.
Burning fat produces no lactic acid. When running near marathon pace using glucose as fuel, some lactate is produced. The lactate itself can be re-used as fuel, especially by the heart, but the inevitable acidity in the skeletal muscles contributes to muscle fatigue.
Secondly, burning fat conserves glycogen, which is the body’s main source of glucose. It is essential to conserve some glycogen because it is crucial to have at least a small amount of glucose to sustain metabolic processes that can only be fuelled by glucose.
The reason an untrained person cannot use fat to fuel running at a marathon pace is that unless you have well developed fat burning enzymes, burning fat alone only generates energy fast enough to maintain a walking pace. One goal of marathon training is to achieve a situation where you can maintain marathon pace fuelled almost entirely by fat. I am hopeful that my long slow runs of the past two months have almost achieved that goal (even though my wife complains that I have that sickly sweet smell of ketones, a by-product of fat metabolism, when I return from a training run)
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Oct 2014
9:35am, 28 Oct 2014
4,069 posts
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Rosehip
Thanks Canute I appreciate your clear explanations.
So I'm aiming for the same adaptations - with the added benefit of potential weight loss by application of some discipline to my refueling.
Do you agree with the concept I've heard voiced that if you eat a relatively high fat diet overall- your body will find it easier to switch to burning body fat on an LSR?
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Oct 2014
1:07pm, 28 Oct 2014
2,429 posts
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Helegant
Please excuse the daft question: If I start by walking and gradually increase speed, how will I know (while doing it), when I've gone into the next non-fat-burning phase?
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Oct 2014
1:19pm, 28 Oct 2014
11,282 posts
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GlennR
Heart rate is probably the easiest Helegant. 80% of max as the threshold? Canute might have a better number.
If you don't have a HRM try talking in whole sentences (if you don't mind people thinking you're mad - in my case that ship sailed long ago).
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Oct 2014
4:53pm, 28 Oct 2014
2,431 posts
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Helegant
Playng devils advocate for a moment Glenn. If I go for a longer stroll, say (shhh) Trailwalker, my legs will be full of lactic acid even though I can still speak (or weep), so is it that simple?
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Oct 2014
5:00pm, 28 Oct 2014
23,075 posts
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HappyG(rrr)
What's Trailwalker?
HR is the best way to measure being in the fat burning zone. Hadd training (HR based training - very much on the polarized principle) will have you running very slowly, or even walking, depending on where you start from, for many months, as you build up that endurance (fat burning) ability. That's why lots of long, slow running (or walking) is good for marathon training. You still need to do some speed work too, in order to increase your pace, esp sub lactate threshold.
But walking so slowly that your HR isn't even in fat burning (below 70%) is no use either. It's great for recovery, and general cardiovascular fitness, but doesn't encourage or build fat burning.
BTW, for calorie burning (i.e. for weight loss) - higher intensity is better e.g. 1 hour of aerobics or 1 hour of fast running, is better than 1 hour of walking or slow running. But if you are a marathon runner, that's tough - cos you have to do the slow running. And if you find a bit more time in your life, 3 hours of slow running burns more calories than 1 hour of aerobics class or 1 hour of fast running. But you have to put the time in! G
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Oct 2014
5:10pm, 28 Oct 2014
2,432 posts
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Helegant
Trailwalker is 100km in 24 hours along the South Downs Way
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Oct 2014
5:12pm, 28 Oct 2014
1,714 posts
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Ceratonia
Trailwalker is an Oxfam charity event, 100km walk/run in 24 (or maybe 30? hours) with the original UK version being over the South Downs & co-organised by the Gurkhas. I'd say a marathon was good training for Trailwalker, rather than the other way round!
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Oct 2014
5:16pm, 28 Oct 2014
4,074 posts
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Rosehip
:)G - I thought "fat burning was 50-70 % MHR when supposedly 85% of energy comes from fat - the presentation SPR linked to might indicate 55% is the lower boundary. Anything over 70% surely you are talking mainly carbs?
Helegant - that sounds fab
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Oct 2014
5:22pm, 28 Oct 2014
2,434 posts
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Helegant
Oh no Rosehip - it wrecked my knees last time; I won't be doing it again until my knees work properly. Too much pain!
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