I have been a regular morning walker for decades. Earlier, I used to walk for maximum one hour at a natural, leisurely pace. I used to feel energetic throughout the day. A few months back, I started walking upto 70 , 80 or 90 minutes, that too at a brisk pace. The result—I started having fatigue and tiredness or pain in the legs , lasting till evenings. I also came across many morning walkers who walked at fast pace ( ultra brisk) for 6 or 7 km every day and developed severe arthritis/synovitis of the knees in later years.
I realised that too much walking or too brisk walking at unnatural pace is harmful for health.
The above is also borne out by Ayurvedic principles which state that too much walking leads to vitiation of vata in the body.
I reverted to my earlier habits of walking less and at leisurely pace and no longer suffer fatigue or pain in the legs.