This is another post in our series of Fitness Saturday exercises and workouts appropriate to women in the second half of life. Personal trainer Brooke Marrone, president and founder of Brooke Marrone Fitness, in New York City, is our fitness guru.

Standing leg extensions are one of the best and most safe knee strengthening and balance exercises. The primary muscles worked are the quadriceps, which are located in the front of your thighs. Try this move 2 to 3 times a week and you should see immediate results!

1. Stand tall with your feet a few inches apart, shoulders back and abs engaged. Find a focal point to look at throughout the exercise.

2. Bring your right knee up to a 90-degree angle in front of your body and flex your foot. Do not compromise your posture (allow the shoulders to roll forward) or bring the knee up higher than the hip. Make sure you can hold this position for at least 30 seconds before you attempt to advance.

3. You can keep your hands in front on your body, straight down by your side, or clasped behind your back.

4. Keeping your body strong and stable, extend your right leg out straight in line with your hip, getting a good squeeze in your quad and trying not to drop your knee. With your leg fully extended, you should be able to see the bottom of your shoe in the mirror.

5. Bend your heel back into your 90-degree angle and repeat. If you cannot maintain proper posture or feel any pain in your low back, start with your knee slightly lower than your hip and work your way up to a 90-degree angle.

6. Be slow and controlled, and remember to breathe. Do two sets of 10 to 15 reps on each side.

Beginners: Place the foot on the floor after each rep. When you are ready, aim to get 5 in a row without coming down, and then 10.

Advanced: Do this exercise on a balance disk for a greater challenge.