My two cents, Have been LCHF committed for 9 months, log on average 30 hours months, but all done with watts in structured sessions. So very little riding and mostly training, there is a massive difference in intensity between the two I find. Initially I had a good response and felt no real difference in my ability and output, taking no carbs and significantly less water on rides up to 3 hours ( don't really do much training longer than this currently ). Then after couple of months found that on higher intensity rides over 2h20 the wheels literally came off, obviously a problem when doing mtb races. I persisted for a awhile thinking it was a process of adaption, but have come to realise the simple fact, if you are going to exercise at 85% plus of heart rate for more than 2 hours, fat oxidisation is not going to be able to provide you with sufficient fuel quickly enough to prevent you from depleting your onbody fuel faster than you can replace it. I now take a 50% diluted 32gi fluid mix and a energy bar that has the highest fat and protein content I can find. I start consuming before the intensity has been sustained for long, as if I wait I find it is too late to try and recover the deficit created in glycogen stores. I did a 3 stage race this weekend. 58km 2h27 avg hr 157 65km 2h45 avg hr 153 57km 2h45 avg hr 153 My max heartrate on bike 178 ( 41 years old ) Each day I had 1 750ml bottle of diluted 32gi and one hammer recover bar on the ride, this kept me strong until finish. I have noticed that the rpe for me is different now than how I remember it, my legs feel tired and as if lactic acid is building up way sooner that when I was carb fuelled, but this is a mind game, as if committed I can push and hold this feeling despite not enjoying it and achieve as good a number in watts as when carb fuelled. I have for some time done 2 x 20min intervals on Kloof in CT for my threshold power. When carb fuelled my recent avg 299 watts ( weigh 69kg ) and drop 4/5% on second one, I seem to recall it a case of the heart and lungs feeling like they where the restrictive part of my performance and less the legs. I recently did the 2x20min fully fat adapted, it dint feel good and legs felt like they struggling from early on in the interval. The big surprise for me was a pb this year of 306 and 305 watts for the two intervals ( still 69kg ) . Had I not had the numbers to compare there is now way I would have ventured them to be my two best intervals this year. It taught me that I need to get used to a different feeling when in the 'hurtlocker' than I have been used to. This brings me upto my last observation, I have been carb fuelled teaching my body how to react under stress in exercise foe over 20 years, now that I am fat adapted for 9 months how realistic and reasonable is it to expect my body to come anywhere near the efficiencies and feelings I know with the latter system ? I do wonder what would be achievable under multiple years of sustained high intensity training as a fat adapted athlete, in my mind I am sure the body will continue to improve the 'system' as it comes to realise it is adapt or die time .. a side note, prior to really embracing LCHF I was weighing in consistently at 73kg , subsequently I am now at 69kg, if one looks at my watts/kg , then actually despite struggling with intensity I have had a solid improvement on that figure.
