Metabolism and endurance running

iVillage Member
Registered: 03-15-2004
Metabolism and endurance running
3
Sun, 05-08-2005 - 8:36pm

This is a science question so I need the gymrat-geeks to give me your thoughts. :)

I know we've talked here about the metabolic pathways (aerobic and anaerobic glycolysis and fatty acid oxidation) and I'm wondering how this applies to endurance running. Science says that your body hits fatty acid oxidation at about the 20 minute mark and your body is essentially using fat to fuel the exercise. So, assuming that's true, why would a runner need to supplement with gels on long runs? Obviously, you have glycogen depletion but if your body switches to using fat, why would that matter?

Thoughts?

iVillage Member
Registered: 03-20-2003
Sun, 05-08-2005 - 9:02pm
Just a guess but I don't think the body switches 100% to fat.





iVillage Member
Registered: 03-11-2004
Mon, 05-09-2005 - 9:51am

that's right, you aren't burning 100% fat, and if you are racing or trying to hit a certain speed goal (like a marathon under 4 hours), you don't want to rely on the fat burning. fatty acid oxidation requires a lot of oxygen to burn fat (hence the term "oxidation") - how much energy you can get from fat is limited by how much oxygen you can get in. so if you are pushing yourself hard (like running up a hill, running faster than a comfortable jog) you are going to be getting out of breath and limiting the fat you can burn. so if you want to keep going at that pace, you'll need to burn glycogen to supplement the fat you are burning. if you run out of glycogen to burn, you bonk. that's why endurance athletes eat gels, etc.


and it's also why i answer the question about the "fat burning zone" the way i do - yes, intense exercise burns more calories (and therefore more fat) than "staying in the fat burning zone" - BUT you can only exercise so long at that intense pace before you either bonk or have to take in carbs to avoid bonking. if you stay "in the fat burning zone" you can continue to exercise much longer and therefore OVERALL burn more calories and more fat. so that's why i always say to maximize fat loss, mix up short intense sessions with long, easy and moderate sessions.


the only time you are burning near 100% fat is when you are breathing easily and oxygen is not limited. like when you are doing yoga or walking, etc.


here's a good article on running and nutrition... http://www.runnersworld.com/article/printer_friendly/0,5046,s7-53-84-0-6263,00.html

iVillage Member
Registered: 03-15-2004
Mon, 05-09-2005 - 11:27pm
Really interesting Jen. Thanks for the article link too.... really enjoyed it!