I don't know if any protein muscle would be broken down during exercise, as the muscles would be burning fat as fuel once glycogen stores were depleted - but I doubt it. As long as an adequate high protein/carb refeed is done afterwards and calcium, magnesium and vitamin D levels were adequate, I expect the body would be able to repair any damage to muscle fibres incurred through the exercise. Otherwise there's risk of muscle loss through metabolism of damaged fibres post-exercise.
I've heard that it's very painful when a marathon runner's glycogen stores run dry and they hit the wall because their muscles are then fuelled only by fat. Knowing this, I have no intention to empty my muscles' glycogen stores while I exercise.
Last edited by paleo-bunny; 02-01-2012 at 10:45 AM.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.