No. As the intensity of the activity approaches and exceeds lactate threshold (LT) the preferred energy substrate is glycogen stored in muscles and the liver. Lipolysis peaks, but levels out once you've exceeded LT.

If you 'bonk' (deplete your glycogen stores - which is more time and intensity dependent than mileage dependent which is also dependent on your level of fitness and how well you repleted your glycogen stores) then your body slows you down so that you can utilize fat for fuel, but there is up to about a 10% contribution from lean body mass as well.

No matter what, some lean body mass contributes to supplying energy, but it is much less a contribution if you supply carbohydrate.