You do not have to be a professional to train like a professional athlete. The objective of Alan Smeets Training is to offer professional coaching to a wide audience.
When you ride your bike in the mountains it will be more difficult when altitude increases. Because of the altitude, your power output will be lower for the same relative intensity.
Most people exercise to improve their fitness. Occasionally, it happens that you can't train for a few days, weeks, and even months because of injuries, illness, or other activities.