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Under Armour should make Lululemon nervous.

The apparel category grew 22% in net revenue at $2.80 billion in the past year.

Lululemon has not reported its annual results yet, but in 2014, the company reported annual net revenue of $1.8 billion.

Although Under Armour is technically bigger than Lululemon, Lululemon's strong point is its women's sector.

Although Under Armour does not disclose revenue by gender, consulting firm Conlumino estimated that Under Armour's business approximately splits at about $1.14 billion for women, and $2.69 billion for men, meaning that the men's sector makes up the bulk of the business. Conlumino estimates that Lululemon's business, though smaller, has a larger women's sector (a estimated $1.72 billion for women and $0.33 billion for men.)

But now, Under Armour is threatening Lululemon even more by zeroing in on its women's business for 2016.

CEO Kevin Plank said on a recent earnings call that he plans on growing the women's business to be "at least as large if not larger than our men's business."

If Under Armour's women's business was bigger than $2.7 billion, it would trump Lululemon tremendously, and arguably usurp the company entirely.

And the company already has momentum.

Plank mentioned that Under Armour's women's brand was the number one selling category with ecommerce, and that's growing more rapidly than either men's or the youth category.

"At current growth rates, Under Armour’s women’s business should be bigger than Lululemon’s by 2017, " Neil Saunders, CEO of Conlumino, said in an email to Business Insider. "Interestingly Lululemon is trying to grow the men’s side, however, while it is having some success I think it is much more of a challenge for it to do this than it is for Under Armour to move into women's."

"As such, Under Armour’s stated intention is worrying for Lululemon. Certainly not all of the customer overlap and Lululemon has some strong levels of loyalty among its female customer, but this represents yet more competition in a market that is already quite crowded, " he wrote.

Misty Copeland has helped sales soar at Under Armour.

One reason for this success might be that Under Armour has something Lululemon doesn't: a star spokesmodel.

Copeland is a large force behind the "I will what I want, "campaign, which seeks to empower female consumers.

This is a huge disparity from Lululemon, which utilizes "brand ambassadors, " or local athletes or yogis, as opposed to celebrities.

Lululemon, however, has cultivated a community that helps set it apart from its competitors. It keeps customers coming back through offering events like free yoga classes and running clubs.