Fatigue

Hi Paul,Are you running in hotter temps than you are used to? This can tire one out. Do you have any health conditions? Asthma? Do you drink alcohol the day before your run, as this can cause muscle weakness and fatigue. Your training may not be allowing you for enough rest....and it catches up to you over time. Does this sound likely? Are you following a periodized plan that allows for shorter runs, easier runs, hillier runs, and long slower ones...that build on your longest distance slowly? This type of training (periodization) will help to get fitter, and also allow for the rest that is needed. Add the artful mix of this with swimming and cycling, and if it is not quite right- fatigue and "flatness" in the legs comes on. I personally would use this as feedback for your training and recovery methods, and take some well thought out days of recovery, and reassess.

Have you changed anything in your diet? As you ramp up training, you also have to ramp up eating.

I went through something like that once, and it turned out that I was having trouble with iron-deficiency anemia. Are you getting enough iron in your diet? Check with a doctor before you start popping iron supplements though, because you can overdose on them.