Here I am wearing the 40 lb vest over the 60 lb vest

100 lbs quite comfortable initially but it gets the heart rate up very quickly. I only trained for 20 minutes doing hill walking outside but I will build up the times in coming months. Basically it feels little worse that the 40 or 60 initially but things change fast.

Special forces train with 100 lb rucks often including shuffle runs and workouts lasting hours.

Weight this heavy is not used all the time though.