This study aims to investigate how professional fitness trainers use four different social platforms; Facebook, Instagram, Twitter and YouTube professionally and what type of content they create. It also explores the specific aspects of each social platform in terms of features or general perception that affect how professional fitness trainers experience them and use them in their professional practice. The qualitative study revealed that professional fitness trainers use all social platforms professionally; to build and sustain their social media community, to educate themselves with fitness knowledge, to make social connections and to advertise themselves as expert fitness trainers. The qualitative study also revealed the unique features of each social platform and how professional fitness trainers engage with same activities differently from one platform to another. The findings support the use of social platforms for fitness purpose professionally and can also inform the design of technology that uses social media to help people stay fit and share fitness information.