As part of my fat loss program I ride my bike for 1 to 1 1/2 hours 5 times a week at 75% of max heart rate. Around 45 minutes to 1 hour into the ride I feel the quads starting to exhaust or at least getting weary. Is this a fair indicator that I am burning the maximum amount of fat for energy or is it an indicator that I might be getting into trouble with muscle loss?

after 45-60 min. of bike riding at 75% i would think your quads WOULDget weary.Try mixing up your cardio.

after 45-60 min. of bike riding at 75% i would think your quads WOULDget weary.Try mixing up your cardio.

The question is.. after that 45 min to 1 hour and the quads are getting tired, are we getting into catabolism or switching to fat burning.

45 minutes at 65 - 75 % of max heart rate is more than enough for fat loss. My opinion , do 45 in the am fasted and do a half hour of weights later in the day ( at least 8 hrs. after cardio ). Break it up a little , thats wayyyyyyyy to much time on the bike , definately gonna eat up some muscle.

Just my 2 cents.............