Staying in our comfort zone is the easy option, but if we keep doing what we have always done we won't change, we won’t see results. Our bodies are very happy living in a homeostasis state. It’s up to us to push ourselves. Change starts the moment you step out of your comfort zone. When you go for your next run - try do an extra 1km or add a couple of sprints at the end. If you go to the gym increase your reps/weight or try something totally different to what you usually do. If you feel like you are really stuck in a rut consider investing in a personal trainer. Their job is to help you along your health/fitness journey challenging you each step of the way.