When i hear this term i picture It's a young lady who enjoys working out in a gym (resistance training) regularly, and has the physique to show it - typically implies thicker than a pilates body with more muscle definition. A runners body for example would usually imply runway model proportions, ie very slender and long legs, with a wider but flat and strong core and less defined waistline. For a gym girl I think of feminine athletic curves with a tight or softly defined midsection, shapely round butt, toned arms and round shoulders, and muscular legs and back. You kind of have to eat a lot consistently and strictly healthy too to see your body grow and keep a muscular form. A "gym body" is hard work to maintain in many ways. The thing that makes this request narrowed is the OP wants brunette and white. There are many girls in a city like Vancouver who fit the description but have different colour hair and are a different racial background. Harley Fox may be the most well known example of this in the industry as an IRL bikini competitor but she's mixed and her hair is black so I didn't suggest her in this particular thread. Actually posted a response to a similar thread recently
https://perb.cc/xenforo/threads/looking-for-a-fitness-yoga-type-hottie.335459/post-2436831