Video - O'Driscoll takes part in the infamous England 7s 'Death Zone' session

With the HSBC Sevens World Series set to kick off this weekend, former Ireland captain Brian O'Driscoll took to the pitch once again - this time for a gruelling training session with the England Sevens squad.

As an ambassador for the HSBC World Rugby Sevens, we are quite used to seeing O'Driscoll in front of the camera giving us his views and expert analysis, yet this time he decided to try out an infamous session known as the 'Death Zone'.

The term 'Death Zone' comes from mountain climbing and describes the altitude at which there is not enough oxygen for humans to breathe.

Despite retiring in 2014, O'Driscoll says he wanted to take up the challenge to see if he could get his brain to "go to a place I used to be able to go" after leaving the game. In a raw and emotional video, we see him talk about the mental strength the game takes and describing how he doesn't know many fifteen players who would be 'capable' of it.

"These players are different than most, and that's what allows them to get into that horribly dark place".