There are 2 main components when u start trekking:
- how are u able to adjust and co-op with breathing issue due to low oxygen
- your physical fitness
For starters, even if u r physically fit, the first component will play a big role. You can work on your fitness but managing low oxygen needs experience on the treks and after every trek, your breath management capability increases.
These treks are normal in altitude with maximum at 11,500 ft which can be managed with good physical fitness.
