I'll be the first to admit, some days I struggle with the purpose of certain movements in a workout. Handstand push ups, landmine chest presses, bear crawls... How will these apply to my real life?I know I'm not alone.Then I ask the harder questions."Why go heavy? Why go fast? Why do this at all?"Here's why.When we workout at a certain intensity or weight, our bodies are quick to adapt to that stimulus. CrossFit encourages us to push our limits -- to lift heavier, have more reps or less time across the 10 principles of fitness (see here). So later in life, when we have to operate at that intensity or weight (or anything less), we will have the capacity to perform. It literally is training our bodies for the unknown and unknowable, not just for today but for 5, 10, 20, 50 years from now.I deadlift a 250# barbell so I can lift a trailer onto a car hitch. I improve my anaerobic capacity in case I ever need to swim extremely fast to save my child from drowning. I perform hundreds of planks and toes-to-bar to securely brace my midline so I can shovel loads of snow without hurting my back. I'm essentially creating a buffer between a real life situation and what my body is capable of. The higher the capacity, the more capable I become.What's more, intensity and weight helps ward off illness. Lifting heavy strengthens bones to help stave off osteoporosis. Anaerobic activity strengthens the heart to ward off disease and high cholesterol. Even an injury can recover faster (and not be as severe) because our bodies are familiar with stress and repair.So, when you see the movements on the whiteboard and start asking the big questions, remember working out is an expression of the capacity and durability of, not just your body, but your life.