Q: I am a 21-year-old male who has been lifting weights and exercising regularly since I was 19. I have always done squats, leg extensions, leg presses, and hamstring curls for my thighs. I recently substituted lunges for squats and the next day I could hardly walk. Why? - M.W., Thornton, CO

A: Your muscles paid you back with soreness because you asked them to do something they weren't used to. Many of the exercises you have been doing emphasize the concentric or shortening phase of the muscle; the eccentric (lengthening) phase of these exercises is commonly overlooked. With leg extensions and hamstring curls, the exertion phase of the exercise is very controlled; however, many people return to the starting position rather quickly and sacrifice the lengthening phase. The same is true for leg presses: people press the weight up and away from the body with great force, only to lower it quickly without really controlling the eccentric phase.

In general, the squat emphasizes the concentric or shortening phase of the exercise as well. Lunges, on the other hand, tend to emphasize the lengthening phase. With squats your feet are planted on the floor at all times; lunges require you to place and rebalance your body with each repetition. You must control the speed of the lunge and balance your body as you lower towards the floor for a longer period of time than with squats. You also slowly lower your body through its full range of motion when doing lunges; usually, the range is greater than that used in squats. It is this extended eccentric or lowering phase that tends to bring on increased muscle soreness, because the muscles are being worked in a different way than that to which they are accustomed.

Lunges are a great exercise for your thighs; just remember that whenever you add a new or different exercise to your routine, you should do so slowly. Any change to your exercise selection or execution may result in soreness the next day. Stretching your muscles thoroughly after exercising may decrease the amount of soreness you experience.

Source: fitlinxx.com