Andy Murrayhas revealed that despite becoming world number one at the end of 2016, it was the "toughest three, four months" of his career.
The Briton ended last year with a run of 24 consecutive wins as he became the top ranked player in tennis for the first time in his career.
However, 2017 has been anything but the same as despite winning his first title in Dubai, Murray crashed out in the fourth round of the 2017 Australian Open before losing early on in Indian Wells, Monte-Carlo and Barcelona.
With a record of 16-5, the 29-year-old has only won three matches since February in a year that has also been plagued with niggling injuries.
Having previously mentioned that he would have done things differently after becoming world number one such as taking more time off a busy schedule, Murray discussed how tough his journey was to reach the pinnacle of tennis.
"The end of last year was like the toughest three, four months of my career to try to get to the No 1 spot," he said, as quoted on Sky Sports. "It took me 12 years to get there, so it's a pretty long journey and that's pretty hard in my opinion."
"That's a lot of work that has gone into that so and then this year, as I've been reminded a lot is that I haven't done well this year, I've not played well, but I'm still No 1 in the world. I have been for the past 25, 26 weeks, but I have not been playing as well. I've stayed there based on all the hard work I put into last year, so in my opinion it's been harder to get there."
Murray will now feature in Madrid and Rome before the French Open and will begin his grass-court season shortly after at the Aegon Championships prior to Wimbledon.
Looking to reach top form following an elbow injury, the reigning Wimbledon champion hopes to continue his stay at the top of the rankings.
"If you want to stay there [number one] for an extended period and stay there for two, three, four years, then obviously that's going to be incredibly challenging," he added. "But right now, at the end of last year was tough for me and took a lot out of me. I would say getting there was harder for me personally."
The Mutua Madrid Open qualifiers begin today (5 May).