It astounds me that so few runners know of or use "Phos Fuel" by Twin Labs. It has transformed me and my training friends by quantum leaps. Perfectly legal & safe, follow directions CORRECTLY. I have not bonked nor even gotten close to it since taking it as directed. My 3:10 PR quickly dropped to 3:01 at Steamtown & Baystate without an increase in training (only approx 40 mpw). Obviously you still need to train, hydrate properly & hit the right day. But this stuff is the best. It delays lactic acid buildup & I have less soreness the days following. It's just what the Dr. ordered, without prescription! Available at most health stores near me in CT.