If taking a guess at it, how much of a drop off in ability do you believe is normal on medium to long rides (>60km)? I think that I drop off too much, my guess (hard to say for sure without expensive power output equipment) is that my ability drops back by about 40%. I'm sure that some drop off is normal, but I had hoped that it would be no more than 20%. I had hoped that if I have a certain muscle power output and cardiovascular ability, provided that I don't overdo it during a ride (staying below the lactate threshold), and provided that there are sufficient nutrients for the muscles, I should be able to maintain power output (within the max 20% drop off that I'd expect). For as long as I can remember I've had this problem of losing a lot of my ability on medium to long rides. About a year ago I became more serious about cycling and I'd like to find a solution to this problem (if indeed it is abnormal). The drop off I experience is gradual, not sudden, which to me suggests that it is not the bonk. (I've bonked more times than I care to remember in earlier years, and afaik it characterised by a more sudden drop off) Things I've tried so far: 1) drink more (currently I consume 2L of fluids for a 4 hour ride) 2) switch from water to isotonic sports drink 3) snack on fruit grain bars during medium to long rides (~ one every hour), on >5 hour rides I also take sandwiches with me 4) stay seated for climbs (preferred to climb standing previously) 5) maintain a cadence of >80rpm 6) get out and ride more (twice per week instead of once per week) None of these things has made a significant difference, although remaining seated and maintaining a >80rpm cadence did help noticably. I've recently started using a heart monitor to make sure that I wasn't overdoing it in the early stages of a ride. I haven't yet used it enough to be sure, but early impression is that I stay within the recommended 90% of my maximum heart rate. My usual training ride is 84km whch includes ~1400m of ascend. The loss of ability is gradual, but I'd guess that after about 60km I'm down 40% compared to my ability in the early stages. Early in the ride when I'm still feeling strong my heart rate can easely rise to about 170bpm, after 60km when the strength has gone my heart rate hovers around the 150bpm mark (when climbing). Any ideas?