How to eat correctly for long training sessions

Eating correctly on long training sessions lasting more than 60 minutes.

The body can survive for up to 10 days without food because of its stored energy. When exercising below 50% of maximum heart rate you mostly used stored fats, we mostly exercises faster than that so we need calories to top our requirements up. If you train regularly your reserves are always lower than they should be that is why we rest up before an important or long event for our body to over compensate and store extra carbohydrates.

An easy way to estimate how many calories you need say on a long bike 3 hours is to do the following If you estimate that you need 700 calories an hour for a medium to hard ride then you need 2,100 for a three-hour bike. Due to the intensity of the bike eating that many calories would be impossible as to divert blood to your digestive system instead of the much-needed muscles would result in you dramatically slowing down. It is therefore widely accepted that you require (between 30-50% of this in energy)So 600- 1,000 calories spread over 3 hours equates to 200-333 calories per hour.

For example with power bars generally having 230 calories cut into four pieces have a quarter once every 15 minutes or a third every 20 minutes. A good help is to have your watch on count down repeat to go off every 15-20 minutes to remind you to eat. Athletes can burn up more calories by consuming energy during a session lasting over 60 minutes because they work at a far higher rate, than just drinking plain water. The intensity soon drops when energy levels drop due to little or no calorie intake.

Possible causes of hitting the wall.

Increase in training intensity & frequency, especially new sports like swimming, the body takes time to adjust. Too high an intensity for your current level of fitness for the specific sport.(Even world class marathon runners who are injured switch to cycling to maintain fitness hit the wall during a moderate training cycle session because of the different muscle groups involved.)
Too cold so the body is fighting to stay warm and exercises needed extra calories.
Not snacking enough in the days prior to a long session.
Not spreading your calorie consumption out evenly during each hour.
Take note of the above to avoid hitting the wall.
Cycling - Trying too hard on the hills.

Running - Starting off too fast or running up hills faster than normal.