It is important to know that very small amounts of dehydration have disproportionate effects on a body’s physical and rational capabilities. It is thought this happens because dehydration decreases the blood plasma volume, which results in less oxygen being delivered to the exercising muscle and brain and increases breathing and heart rates. This decreases sporting performance, coordination and the ability to make good decisions on the football pitch.
Amazingly even low levels of dehydration have physiological consequences. A loss of 2% bodyweight (that’s just over a litre of fluid) causes an increase in perceived effort and is claimed to reduce performance by 10-20%.
On a hot day the recommended procedure is to drink fluids often and early. If you feel thirsty it’s too late you are already dehydrated. So to prep the body pre match try to consume one bottle sports drink 2 hours before kick off and one sports drink 20 mins before kick off, one for half time, one for full time. It is possible for an athlete to suffer from dehydration within 15 minutes in hot humid conditions so water or sports drink should be taken at every opportunity during the game as well.