Is this a bad sign?

[episodic]

I've been biking 10-20 miles 4 times a week + walking 4 miles or so on non biking days for 2 months now. I'm mid 30's and was 340 lbs 2 months ago. I'm 308 as of this morning.

When working out (biking mostly) - my rt knee develops an ache that my left knee never gets. When I massage it after the workout it is 'kinda' painful - goes away after an hour or so. For 2-3 hours, I instinctively 'baby' it. . .

Am I training too hard? I rocked an exercise bike for the 'first' time ever this evening, and I tried to push as hard as I do on the street. This is the first time I've had heart rate, etc. I sustained 150 bpm for 45 minutes continues with a cadence of 90-100 on the hill simulation mode. I was drenched in sweat. This is usually how I work out on the bike, I go all out.

 

[drnickriviera]

Is the pain below the knee cap?
Your bike might not be adjusted properly. I'd take it to a good bike shop and have them adjust it. A 1/4" adjustment in seat height or front to back can mean the difference between pain and going for 3 hours nonstop pain free.

 

[Imp]

Are you seated "properly" on the bike, and is the bike a proper fit for you?

I only have a clue what the proper riding position is, but if your seat is too low or too high, your leg muscles may be put in an awkward position. As to why it's only one leg, we aren't perfectly symmetric.

That or you are pushing it too much and you're not giving time for your muscles to develop/heal. When I bike, my right leg does more work since I'm a righty and kick right.