One key to successful training has to be a certain degree of flexibility. I don't think a week goes by that I don't have to alter my training plans to some degree, whether the cause is weather, scheduling, or whatever.
I'd planned on doing my 3.1 mile run yesterday evening, then strength training at lunch today. But last night we needed to get our son to the doctor (he's been fighting a fever for a few days), and today I realized I couldn't wait any longer to get a hair cut.
So instead I did the run this morning, and will stop at the gym after work. The morning run was probably better anyway, since the dog gets a nice bit of exercise before she's left alone all day, and there's nothing like the feeling of getting a good run in on a beautifully crisp morning like today. Now I've just got to get in the time after work.
Speaking of running, my tendonitis is a minor concern at most now. I haven't tested it over long distances, but the regular 5K has virtually no effect. There's a slight stiffness at the beginning that fades within a quarter mile or so. It may be time to start increasing mileage or intensity next week.
My training log at Beginnertriathlete.com.