With respect to endurance sports where you will exercise long enough to exhaust glycogen stores, you actually want a mix of fructose and another sugar such as maltodextrin.
Cyclists call it 'the bonk' and it's fucking horrible.
It's like been incredibly drunk and tired at the same time.
Happened to me the first time I did a 60 mile ride in winter, wind back was brutal, I got about 10 miles from home on the outskirts of town, found a petrol station ate a cornish pasty and two mars bars and it took about 30 minutes before I could summon the energy to get on the bike and coast home.
I learnt the lesson the hard way that day.
I've found it relatively easy to avoid since mostly by drinking at least a litre of isotonic an hour on the bike (adjusting for climate) and eating reasonable amounts of carbs the day before.
http://fellrnr.com/wiki/Fructose
http://fellrnr.com/wiki/Nutrient_Timing
When you hear a marathon runner refer to hitting the wall, what's happenened is that they've exhausted their glycogen stores.