Ireland second row Iain Henderson says the team must have their "heads screwed on" to overcome Japan in the Autumn Nations Series opener on Saturday.

"They are impressive - they shock teams and audiences while they have incredible pace throughout the team," said the Ulster lock.

"I'm incredibly excited about the game and everyone else should be."

He added: "They work together as a unit and have players who do simple jobs really well. Most sides who suffer against Japan get shocked by how fast they are and the tempo they play at.

"It's something we're fully aware of and trying to account for so we must make sure we have our heads screwed on."

In-form Irish

Japan will bring good memories of that 19-12 group win in Shizuoka to the Aviva Stadium but they went on to lose 39-31 to Ireland at the Dublin venue in July.

It was one of five straight wins which have boosted Irish confidence and Henderson hopes to carry positive momentum into the game.

"One thing that frustrated us at the start of the Six Nations was that we were unable to put in complete performances for a full game," he said.

"We started to hit our stride towards the end of the Six Nations and over the summer series. We have spoken briefly about not waiting to pick up where we were before that but trying to start with that momentum and carry it on.

"It's something that's been a real focus for the players - we are not coming back to re-learn, we are coming back to pick up where we left off.

"It's something that's quite exciting and it's definitely challenging with new players coming in. Hopefully this weekend we'll see a continuation of the form from the last five matches."

Henderson has played just one game since the summer Lions tour because of injury and knows he is not assured of a starting spot in Dublin.

"It's been incredibly competitive during the camp but in a very positive way. The competition just makes it more exciting and that's adding to my excitement for the game on Saturday," he said.

"I'm trying to give my all whether it be in training or in a performance for Ulster. Andy Farrell is an incredibly experienced coach and I trust him to make the best decisions for whatever is right for the team. I'm going to try and put my hand up as best as possible."