There could be a few possibilities.
1.The position that you may have used may not have been a comfortable one.Too much of strain could have caused the cramps.
2.You may have been too tight which would have resulted in reduced blood supply to the muscles and the eventual cramps.
is another factor precipitating factor for cramps.Either reduced water intake or excessive loss of water from the body could cause this.
4.Electrolyte imbalances like hypokalemia
may also cause cramps on exertion,but its difficult to predict and the best way to confirm is to check serum potassium levels.
is a definite possibility.Hyperventilation washes away the carbon dioxide from the body resulting in respiratory alkalosis
. This interferes with calcium metabolism
and results in cramps and tetany.
Hope it was useful.