For the last 3 months, I've been consistent with a weight-lifting regiment in order to help me loose weight and get fit; so far I've been following a book's training plan, which ensures that I have enough variability in my routine; essentially I lift weights three times a week and do aerobic exercise (stationary bike) 3-4 times a week (different days). Anyway, I've been making progress both loosing weight and increasing the amount I can lift.
As of 2 weeks ago, I was doing 375 on the leg press. Then I took a week off from weight lifting (following the handbook). Today, I couldn't push the leg press in position above 310. This is a bit disturbing to me because it's a huge drop. But when I did leg extensions and leg curls, I didn't have any decrease in ability (170 and 120 respectively).
The reason why this concerns me is I am still keeping my calorie intake low (1500-1700) and increasing the amount of exercise; recently, I just started jogging. At 5 feet 11 inches, I am about 190 pounds. A year ago, I was about 275. While I certainly don't starve myself (one reason I decided to exercise instead of lowering calorie intake to untolerable low amounts), I am worry I might actually be loosing muscle mass with the fat I am burning off.
Should I be concern about loosing muscle mass?