Personal energy requirement=basic energy requirements + extra energy requirements
Basic energy requirements
For every Kg of body weight 1.3 calories is required every hour. (An athlete weighing 50Kg would require 1.3*24hrs*50Kg=1560 calories/day)
Extra energy requirements
For each hours training you require 8.5 calories for each Kg of body weight. (For a two hour training session our 50Kg athlete would require 8.5 * 2hrs * 50Kg=850 calories)
An athlete weighing 50Kg who trains for two hours would require an intake of approx. 2410 calories (1560 + 850)