Over-training?

Question
Hi,
I workout daily for about 2 hours, first alternating running/walking at a steep incline for about 50 minutes, then a 45-minute spinning class.  My heart rate usually goes up between 156 and 165 (I'm a woman, 5'4", 125 lbs, 42 years old and very fit).  But for the last month or so I think I may be working out too hard because I give it all I've got and I can barely get my HR up to 155 and I feel exhausted, plus my quadriceps and calves feel really sore and tired when I climb stairs during the day at work.  I have to cut down on my workouts a bit because I'm also having trouble with an old knee injuring I got from running.
Anyway, my anxiety is about the fact that I've gotten to a level of fitness where I'm comfortable with my weight and I eat healthy foods but I don't have to be on a diet.  If I cut back on the intensity or duration of my workouts I will be burning fewer calories and the whole equation will be unbalanced.
I think I'm over-training and I don't see how I can cut back without gaining weight in the process!
Please help!
Grace

Answer
Dear Grace,

You should know that DURATION, not intensity, of exercise is the determinant in caloric expenditure.

You are definately overtraining so cut back on trying to maintain the heartrate at your previous level and increase your time during aerobic exercise. Try some various other aerobic exercises (called crosstraining) also. Take some time off in order to recover properly.

You'll not lose conditioning and you will maintain your weight without serious consequences.

I hope I have been of some assistance.

Dr. Christopher Rampacek