hi, i have 23 years old , i practice fitness ,, i feel an instability on my knees while walking , i feel a weakness too on my legs , i have a flat feet , when i woke up i feel that my left knee is blooked , but when i m walking and movinig it in a while i lost that feeling , and it s comes over when i set to mush or after sleeping , and when change the shoes for exmple my knees come to pain on the miniscal tears i think , i m suffring can you help doctors ?