Now if you are familiar with the TIU girls, then their workout challenges might strike you as surprising, given our fitness philosophy , which focuses on rational fitness (which is exactly what it sounds like). In the past, many of the TIU challenges have focused on literally whittling your body away, and participants were encouraged to measure their body parts in order to track progress — they even sell branded tape measures for this exact task! But Karena and Katrina must have caught on to the fact that when you focus on what your body can do and how you feel, rather than how you look, it's healthier and more sustainable. (And it also just makes more sense.)