As a result, he was rested for Ireland's summer tour to Argentina but despite his initial disappointment, O'Brien believes this could prove to be a blessing in disguise.
"The last proper pre-season I had was in 2011," O'Brien told the Irish Independent. "I definitely think it stands to you throughout the whole year.
"You don't pick up as many knocks, you're fresher, your body is able to last the whole year.
"That's what we've done this year and this will be the first time I've a lot of stuff under my belt.
"I'm moving very freely at the minute. I've nothing annoying me or anything like that and that's also the first time in a good while that I've been like that.
"Not going on tour probably had a big part to play as well. I had complete rest and just got the feet up for a while."