Nairobi, Sept. 2 -- Every month, another marathon appears on Kenya's race calendar, and for Caroline Njeri, that means more runners walking into her shop looking for a new pair of shoes.

She estimates she now sells between 20 and 50 pairs around major races, a level of demand that would have been unusual several years ago.

As running takes hold among more Kenyans, from members of organised clubs to weekend racers, the country's expanding fitness culture is creating a new market for entrepreneurs selling specialised sports footwear and athleisure wear.

Caroline is not the only one.

Traders of gym apparel and specialised running footwear report rising demand from recreational runners, gym enthusiasts and consumers embracing athleisure a...