Mikaela Mayer can’t sit still.

The morning after her unified junior middleweight title victory over Mary Spencer, Mayer is pacing around her hotel room in Montreal, Quebec, Canada as she talks, adjusting items on tables, checking her lip gloss, investigating every room. One might reasonably think that it’s post-fight adrenaline, euphoria about becoming a world champion in a second weight class simultaneously, a three-division world champion overall, and two-division unified champion, but that’s just who she is.

“My real personality, I never sit still,” Mayer joked. “I cannot sit still. I am constantly moving around. It’s so hard for me to rest in training camp. I’m just like go, go, go. Something’s wrong with me, I don’t know.”

It’s that same mentality, the inability to stay stagnant, that has driven Mayer (22-2, 5 KOs) to new heights in her career. After a pair of hotly contested and animosity-filled victories over Sandy Ryan last year cemented her as WBO welterweight champion, Mayer had options at her disposal. Plan A, so to speak, was to organize an undisputed welterweight title bout with Lauren Price, but after promising negotiations, the bout didn’t materialize.

The easy option for Mayer, ranked ninth on The Ring’s pound-for-pound list, to stay busy would have been to arrange a title defense, most likely against a lesser-known contender. But that would have felt like sitting still.

Instead, she chose an option no one expected, jumping up to 154 pounds to face Spencer, then the WBA titleholder. The pot was sweetened when Cecilia Braekhus vacated the pair of titles she won in her retirement bout against Ema Kozin in early October, and those sanctioning bodies agreed to put their titles on the line as well.

Suddenly, Mayer, who won her first world title five years ago at 130 pounds, was fighting for three world titles at 154. Las Vegas’ Mayer, 35, scored a dominant unanimous decision victory over Spencer to capture the titles in the main event of a sold-out event Thursday night at Montreal Casino.

The bout, broadcast by promoter Top Rank’s FAST channels, was rightfully heralded as the biggest women’s fight ever staged in Canada. The boxing-frenzied fanbase in Quebec reacted accordingly, buying up all the tickets within 48 hours.

Though the version of Spencer (10-3, 6 KOs) that fought Mayer was perhaps the sharpest and most confident one we’ve seen in her pro career thus far, Mayer was simply too persistent and accurate all night long. In order for that to be the case, however, Mayer had to absorb some right hands – particularly whipping uppercuts – from Spencer that would have ended the night for the vast majority of 154-pounders in the world, answering the most pressing of questions that lingered ahead of the contest.

“I didn’t feel Alycia (Baumgardner) or Sandy’s power at all,” Mayer said. “I didn’t feel anything there. Round one, I felt Mary’s. Even at 147, when I first went to 147, I felt the difference with Natasha Jonas, her body weight. But then going to ‘54, I definitely felt the difference with Mary. And it's funny, because in the lead up, at the press conference, she said that. She’s like, ‘You’re going to see it’s a lot different moving up to ‘54.’

“And I was like, ‘Oh, [expletive], maybe.’ And then round one, I was like, ‘Yep, okay, don’t get hit. Don’t get hit clean with her shots because she is heavy.’ And then, of course, I did get hit clean, but I just think I have a gangster chin. I think that’s something no one really realizes about me, but I can take a punch.”

There were also large stretches in the fight in which Mayer appeared to be the one overpowering Spencer in terms of physical strength, pinning Spencer against the ropes for noticeable stretches. Mayer adopted a wider stance on the inside at times and utilized flurries of hooks to occupy her larger opponent.

Mayer and her team, which now sees Kofi Jantuah in the lead chair alongside career-long mentor Al Mitchell, extracted information from Spencer’s bouts against Femke Hermans that indicated Spencer might struggle with defending against hooks. Combined with a new commitment to sitting down on her shots and added physical strength, and Mayer looked like a fighter who would not be pushed around at heavier weights.

“That’s something I’ve been working on,” Mayer said, “because it wasn’t something that I ever had at lightweight just because I’d do all that work and I’m eating 1,100 calories a day, you know, trying to stay down that way. I started to feel it a little more at 147, but you know, it really does take time.

“It takes time to reverse what I did to my body by holding it down at 130 for so long, and I’m really feeling that now. We did a good strength program for this fight, and so it’s one of the reasons I wanted to fight at 154 because I know Lauren Price is strong, and I want to be able to be a competitor at these heavier weights.”

The question for Mayer now is which heavier weight she’ll try to further conquer next. Wales’ Price (9-0, 2 KOs) has recently expressed interest in renegotiating and making the undisputed welterweight title fight with Mayer.

If Mayer were to stay at 154, the path to undisputed could only go through her longtime close friend Oshae Jones (9-0, 3 KOs), who holds the IBF title. Mayer, the WBA/WBC/WBO champ, admits that she doesn’t really want to fight her friend, but that the two could make “great money” doing it were it to either be the only option, or such an enticing financial alternative that it would be unavoidable.

As much as the win over Spencer was a revelation of how a physically transformed Mayer could adapt, strength-wise, to a heavier division, it was also a test to see if her base instincts could still carry her through as a fighter. Just as she can’t outside of the ring, Mayer can’t stay still inside it for long, and was able to maintain her trademark volume even with more muscle mass.

Whomever Mayer’s next opponent turns out to be, it would seem they’ll still have to contend with her punch output, just coming from a bigger, more powerful frame.

“It’s such like a natural response to me,” Mayer said. “I think that’s just where I get my natural style from, you know, it’s like I just think go, go, go, go. I’m trying to think and process more and not just be so reactive. But honestly, it’s a good trait to have.

“That’s how I got through most of my fights is like, I just don’t let up. I just keep letting my hands go. The worst thing you can do is freeze up and let someone outwork you. So, I know no one can do that, and I just gotta put my thinking cap on a little more and just do it.”

For now, her thinking cap is on as she ponders her next move, which seldom takes her too long.