Tiger Woods had many observers wondering what was being applied to his neck and lower back ahead of his opening round at the Northern Trust near Boston

Woods grabbed five birdies in a three-under par 68 and head to the clubhouse trailing four shots behind early leader and fellow American Harris English.

The 15-time Major winning Woods was observed ahead of tee-off on the TPC Norton practice range rubbing his upper back with a towel and placing a cold bottle of water on the back of his neck.

Tiger Woods rubbing hot oil off his back ahead of teeing-up on day one of the Northern Trust

Woods had mentioned last month at the Memorial that he has days when his back doesn’t feel right.

But then there was the sight earlier today with a physio applying ‘hot’ oil to Woods’ neck and lower back, and as it turned out he was rubbing off the excess oil and trying to cool it down with the cold water.

“They were putting some pretty hot oils on there but then my lower back is used to it,” said Woods smiling when asked after his round.

“It’s accustomed to it. We do it all the time just so I can get loose. I decided to put some up on my neck, and it’s not as tolerant as my lower back, so it gets awfully hot.

“It’s common in pretty much every other sport and especially hockey, those guys put some pretty hot stuff on their legs, but you become accustomed to it.

“My lower back is pretty immune to it, but my neck is not.”

He was also asked post his round why the decision to again change putters from the putter he used in his last event – the PGA Championship.

“Just stubbornness, I guess. I practice all the time with — I have been, with a longer putter, and the one I’ve been using that one for 21 years, and then also my 8002,” he said.

“I switch back and forth between all of those. I really do practice with my 8002 probably the most because I like feeling that toe release and I like putting with my right hand. That’s basically my training aid, and then I went to a longer putter to get more reps in.

“I went with it at the PGA, had one good day, the first day, and then after that I didn’t really putt well. When I was at home practicing I didn’t really use this putter. I was practicing with the other one to make sure I could get some reps and get some feel, and all of I sudden — heck with it, I’ll just put it in play and see how it goes, and it worked.”