I have always doen my long runs on empty and there is an article in the July issue of Runner's World.  If I remember correctly it says it trains the muscle to burn more fat and helps boost the capcity to store carbs

I think the work out would have to be fairly intense and for a real long period of time to start burning muscle.

In order of this to happen body fat has to be re-converted back into glycogen. When this happens the sweat from the body will smell like urine --- this is ketosis.

Ketosis is not a bad thing. A prolonged period of ketosis will eventually indicate that the body is eating its own muscle --- but not during the period of time that you are working out.

The best thing that can happen is a little fat was burned. Refueling after the run will bring your glygogen levels into balance.

Went to the local college clean out garage sale today. Stood in line for 1 1/2 hours for the doors to open, so I could see what they had for bikes. Doors opened, I went in, no bikes. Agghhhhhhhhh.

Oh well, it was a beautiful morning, and I got in an 8.14 mile run in 1:08:20.

There are many articles in Active.com that really are helpful. I've saved many in a folder for reference. Regarding the burning of  fat/muscle, there was a good nutrition piece this winter having to do with carb loading:

Glycogen is the main source of energy for long endurance runs. Carbohydrates are stored as glycogen in the liver and in the muscles. Your body can store about 2000 calories worth of glycogen. That's enough calories to provide energy for about 18 miles of running. Once this supply is depleted, the body starts to burn fat. Sounds like a good back-up plan, but the problem is that the body takes longer to metabolize fat for energy.

Ever hear of “hitting the wall”? That’s when a runner's body shuts down mentally and physically. The cause is often from depleted carb stores. There’s just nothing left in the tank; hence the importance of fully stocked glycogen stores before the race. It’s also important to keep these stores refueled during the race by drinking sports drink and/or ingesting other quick carbs such as energy gels, chews, or beans about every 30 to 45 minutes during the race.

Back to carb-loading…past thinking had runners ingesting lots of carbs the entire last week of the taper. I’ve found that the last three days prior to the race is plenty of time to make sure you’re fueled up for the big day.

During this three day-period before race day, your carbohydrate intake should increase to 70 to 80 percent of your total daily caloric intake. That doesn’t mean you’re taking in more calories, it just means that of the calories you’re taking in, 70 to 80 percent need to be comprised of carbs.

Not all carbs are alike, Knowing the differences and eating the right kinds at the right time during the carb-loading phase can make a huge difference. Complex carbs are comprised of unrefined whole grain foods such as whole grain breads, legumes, brown rice, and whole grain pasta. Simple carbs are foods made of refined and/or processed grains such as white bread, regular pasta, white rice, packaged cookies, cakes, and doughnuts. Fruits are technically simple carbs too, but they’re very nutrient dense and I would never put them in the same category as a doughnut. Keep in mind that eating a banana will provide quick energy because your body will process it very quickly, while a low-fat bran muffin will sustain your energy needs a lot longer.

Now that you know the different types of carbs, you need to know when to eat them.

Day 1: The first day of the carb-load should consist mainly of complex carbs (i.e., whole grain breads and whole wheat or whole grain pasta). By loading up on complex carbs the first day, you have time for them to be processed and voided well before race day.

Day 2: Taper off the complex carbs and switch over to simple carbs. Be careful though. Don't load up on tons of fruit and the like, if you're not used to eating lots of fruit. Also avoid loading up on simple carbs that contain a lot of saturated fat (cookies, doughnuts, pastries). The extra fat will slow down digestion and make you feel sluggish.

Day 3: Continue with the simple carbs. Eat your last major meal 12 to 15 hours prior to the race. This meal should be comprised of easily digestible foods that will pass through your system before the race. This is the time many runners turn to a big plate of pasta. Avoid heavy cream sauces and stick with basic marinara sauce.

FYI: Each gram of carbs can store 3 grams of water. So, to make sure you get complete carb storage, drink four to eight glasses of water each day. You may gain a pound or two during this carb-loading phase, but most of this extra weight is water and can actually help you stay well-hydrated during the race. And don’t worry, you'll sweat out those extra “water pounds” during the race.

Tip: Practice make perfect. Eating before a race can be a tricky thing. Test different foods for your carb-loading phase well before race day. Pick one of your longest training runs and pretend it's "race day." Try a mini-carb-loading phase before this run. This will give you the opportunity to see how long different foods take to pass and which ones to avoid because they "hang around" too long.

Note: Carb-loading can also affect your blood sugar levels. Diabetics and others with specific health problems should consult with their doctors and/or a registered dietitian about the best foods to eat during their carb-loading phase, especially if it's your first experience with carb-loading.

Did a long run today of 4 miles. I felt incredible!! Ran it in 42:15, which is over 4:00 better than my last 4 mile run! I didn't feel like I was trying to push it either. All this training is def paying off!! Next week is going to be a true test....2 miles Tues, 3 miles Weds, 2 miles Fri and long run of 7 miles Sat. Sheesh! I haven't run anywhere near that much since I started!!

Dtothe2nd - great time on your 8k!!! Impressive!!

7.15 miles in 1:15. Almost to 90 degrees today.  But it's Saturday, and dagnabbit I wanted to run the River Park trail in Chicago.  I'm glad that one of the connecting parks had one of those children's waterparks with a variety of sprays to walk through.  Don't think I could have made it that far without soaking my head.  I hydrated as often as possible. 

Don't worry, there's still water left in Lake Michigan.  I didn't drink it all.

Now I'll be a couch potato while I watch Poland and the Czech Republic go at it in 75 degree rainy weather from Wrowclaw (sp) in Euro 2012.

0-0 in the first half.

Great post.  Im training for my first marathon.  Im different to you, my environment is about 30 Deg C at 10 in the morning and it just gets hotter.  I live in Gibraltar (southern spain - a British colony) and theres no flat runs.  I have my first big run tomorrow and im dreading it - im sure i'll be fine but ....... I went home to the UK for a week last week and training runs there were a doddle compared to here - 8 miles done in less than 70 mins!

Ran 4 miles Tuesday and 5 on Thursday, then the 5K race for melanoma research, Block the Sun Run.  Managed to beat 30 min again, barely, came in at 29:43.  Warmest race so far this year, but would have been much worse if not for good cloud cover.  The winner of the entire run was in my 55-59 age group, coming in at 18:08!  Seriously! 

I'll try to get in a long slow run tomorrow before church; too warm later in the day.  Plus, it's 34 years tomorrow my wife and I exchanged vows, so we'll be celebrating big time!!

Thanks for the great article.  Good info.!