"If watching the European Championships showed me anything, it's that it's a young man's sport nowadays," Gray told the club's official website.
"It's that recovery factor. If you look at Spain and what they achieved - they seemed to be a yard quicker. It's down to their preparations but also fitness levels.
"If we're going to be playing Tuesday-Saturday-Tuesday, we need a fit side and for players to be available. We need them to be able to recover as quickly as possible."