I have been pondering over nutrition for endurance events (ultra-running in specific) for quite sometime, today decided to jot down some of my experience. Nutrition plays such a key role for any events > 4 hrs that narrowing down the right strategy for oneself is critical to success.
In this section I am mainly going to list some thoughts on calorific replacement during endurance events.
1. Events less than marathon or a flattish 50k:
For events which are less than 4-6 hrs for a 4:30hr marathoner likeme, relying mostly on gels for every 50-1hr is sufficient. Mainly because human body has about 1800-2000 calories in the form of muscle glycogen which is the easiest and quick source body digs into during endurance events. For marathon distance typically one requires about 100 calories per hr, so total required calories is around 2600 calories.
If we are running a marathon in moderate intensity i.e in range of 70% max heart rate, about 70% of the calories are consumed primarily through carbs and rest through fat store. So we effectively need about additional 400-500 calories in the form of gels. So a gel every 50mins to 1 hr works for average athletes like me.
2. Events ranging from 8hr-14hrs :
For a hilly 50k , 50 mile and 100k events, we need to understand which of the refueling sources works for one's body. A good source to understand calorific replacement and various options are:
i) Hammer Nutrition's refueling guide.
ii) Ultrarunning magazine article by Sunny Blende, sports nutritionist.
According to article (i) some of the keys issues to consider are:
1. What is the total energy expended during endurance events?
The total energy expended during endurance exercise, is of the order of 600-900 cal/hr.
But we cannot replace entire calories expended because body cannot absorb and process food at that rate.
2. What is the max that can be processed by the body?
The limiting factors in caloric replenishment are gastric emptying and liver metabolism of carbohydrates. For most athletes, this is in the 240-280 cal/hr range, and this, by and large, sets the limit of caloric intake. If you consume more than that, you will only get some form of stomach distress.
3. How is the difference of calories between expended and consumed is fueled fulfilled?
Mainly by fat store and if the difference is too high it will dig into muscle store(protien) that's when consuming protein during endurance events helps and prevents muscle glycogen loss.
So basically our goal should be to consume around 240-280 calories every hr in different forms. To do that we have host of different options. Specially during Ultra-running you have whole buffet of food at Aid stations, so which is the strategy one should employ, well to answer that one should experiment with couple of different choices during training runs and stick with one that works.
3. Events of distances 100mi :
Disclaimer, not very experienced with the 100mi distances, but same strategy as above has worked well so far. Along with regular energy source some solid food during initial half of the race works well. As the event gets longer we need to rely on some real food as well. Since we will be running at lower intensity digesting solid food should be possible.(specially during 1st half of the race).
Fueling options(not comprehensive)
Gel and semi solid options: Most of the gel options are listed in article (ii) above, they provide about 100 calories in 1 serving. taking 2 gels and some additional calories from aid station in form of PBJ or potatoes works well for many.
i) Perpeteum: Hammer nutrition product this has worked very well during biking events but not so well during ultra-running for me, but works well for some of my other ultra-running friends. (has Salt as well so consider that during electrolyte replacement)
ii) Clip2: my favorite energy refueling source by SucceedsCaps. Each packet has about 150 calories of complex carbs and along with 1 gel every hour works very well. I don't get any sugar highs, body feels great as long as calories are replaced regularly. (has salt as well)
iii) Spitz: haven't used this but heard this works well for multi-day adventure racers.
i) Ensure and Boost: works great as a supplement energy source, it has good amount of protein as well(about 13gm per serving). This is very concentrated drink so diluting the drink helps to avoid stomach nausea.
There are lot of energy bars like power bars, luna, clif bars etc, but bars has a primary source is tough on stomach to digest but works well as supplement. It has been found very effective for bikers though... since bikers don't work that hard anyways :).
Finally goal is to get about 240-280 calories per hour, one needs to experiment and find that works for you during training. As George Sheeshan has been quoted umpteen times "we all are experiment of one".