Hi Alfie, The low HR training talked about here (either Maffetone, Hadd, or Parker) is a little different from LSD. Yes, with each program (MAF, Hadd, Parker), there are certain HR ceilings. Why it is different from Long Slow Distance, is that it is not about SLOW, though it will be at first. Each of these methods is about developing--and getting faster while using predominantly-- the aerobic, fat-burning fibers. Each program recommends basically the same amount of time for the base period. 12-16 weeks (more if you have it, and you are just starting out). If you go with MAF, then you keep all your miles at or below 180-age. If you go with Hadd, then that would depend what your maximal heart rate is. (you can research Hadd). If you go with Parker, then you use 70% HRR as a ceiling. You need to know your maximal heart rate and resting heart rate for this. People have found success with all approaches, or a mix. With each you stay at or under the HR ceiling. About 6-8 weeks out from the marathon, all programs suggest that you add some higher HR miles. 10% of your miles per week is usually safe, but be careful. (LT runs, intervals, tune-up races). Good luck. --Jimmy