from what I understand of the biology, glucose (in the form of glycogen stores) is fuel for flight or fight, i.e. quick local sources of energy and supportive of sprinters and swimmers over short distances. But the real energy needed for endurance events is fuelled by fat (i,e, lipids) hence 'second wind'. which is the body switching from glucose to fat and ketone burning. A glucose snackbar will fuel about 20 yards IMO. Remember the UK Gov sugar tax infographics with the teaspoons of sugar? And how much energy you needed to expend to couteract it?