You might have already noticed a decline of people lounging in their workout wear at Starbucks. But that doesn't mean you'll see less athletic apparel on your local store racks, as companies continue to unveil athleisure lines for fall.

Analysts predict the trend of wearing athletic clothes to do everything--from dressing for work to grocery shopping to, you know, actually working out--will slow. But that hasn't stopped the likes of Alexander Wang and Prabal Gurung from betting on the category's endurance.

The expansion, in spite of slow growth warnings, highlights not only the vagaries of doing business in the ever-trendy fashion world but also the need for speed as an entrepreneur--and the importance of being in the right place at the right time.

Last week, menswear startup Bonobos, which prides itself on offering personalized fit and styling, launched its five-piece activewear line dubbed Good Sport, which consists of basics including gym shorts, long-and short-sleeve tees and hoodies. Prices range from $68-$148 and are available online and in the store's Guideshops.

"We don't think about it in terms of a trend," says Brad Andrews, chief merchandising officer at Bonobos. Instead, he says the company's new line fits with its more traditional scheme. It just has performance attributes and is meant to be worn for active pursuits. "The entrance into this category was about addressing the needs of a customer, so addressing a part of his life we weren't previously addressing."

Andrews explains the concept was created in part due to consumer feedback that shopping online for well-fitting and attractive performance wear proved difficult. Bonobos' solution is to offer gym shorts available in specific waist sizes to ensure a precise fit.

"You know, we've over the years kind of made the evolution from being known for pants to being known for a full menswear collection," says Andrews. "Extending into tailored clothing and active was the next part of it."

But many retail experts doubt companies will be pleased with results from their new lines. "Athleisure has or is topping out," says Jan Rogers Kniffen, retail investment consultant and former retail executive. "It's growth for fall will be flat or even negative."

Kniffen, who was at the Goldman Sachs Annual Global Retailing Conference in New York earlier this month, heard retailers speak about a resurgence in denim, which is a good indicator that many will stop wearing Yoga pants as their utilitarian go-to.

"When you start hearing things like that, it's hard to have two different looks surge at the same time," he says. "It tells you that one is probably fading, and I think that fading look is athleisure."

However, Kniffen says that due to the rise of healthy living, true performance wear utilized for active lifestyles will see very little impact, citing Nike and Under Armour as examples. He also believes men's brands will fare better than women's as guys typically make purchases based on performance and price over fashion.

So what's the upshot for smaller brands like Bonobos hoping to compete with heavyweights like Nike and Under Armour? The way Kniffen sees it, "there's plenty of room in the space if you've got something that's really cool, really interesting, and new and novel and people love it." And if that doesn't work, "you still want to be fashionable in the gym," he says.