What’s the most important reason to be physically active? To feel great, right? Whether it’s the endorphin rush from aerobic conditioning, or the sense of power and strength from resistance exercises, or the relaxation and freedom of movement from flexibility exercises, it’s all about feeling good. So, it’s really frustrating when I see or hear about someone hurting themselves and needing to put their activity on hold—especially when the injury could have been prevented.

One of the most common ways to get injured is to use bad form—that is, to do the exercise so incorrectly that you suffer from an acute (immediate) or overuse injury. Although there are often many variations on any particular exercise, and I encourage creativity in my Nancercize classes, there are some underlying principles that can help you make sure you are using good form. You need proper body position and alignment to get the most out of your effort, to prevent injury, to make sure you’re actually using the muscle or muscle group you’re aiming for; and finally, to prevent cheating. Actually there’s one more thing: it looks and feels better! Where’s the pleasure (or the best use of your time and body) if you’re doing something in a sloppy way?

In my book, Nancercize: 101 Thing to Do on a Park Bench, I give specific pointers for each exercise. In general, the most common form bloopers I see are:

• Shoulders creeping up towards your ears. Correct form usually means keeping your shoulders down away from your ears.
• Your chest collapses inward and your shoulders hunch forward. Consciously drop your shoulders back, and elongate your torso and open your chest by keeping your breast bone up and out.
• Your head falls forward or your chin juts out. Generally, you want to keep your head and neck in line with your spine.
• Your abdominal muscles are inactive and just hanging out. Instead, keep them contracted and engaged as if you were pulling your belly button to your spine. This allows your lower body to align properly.
• Your chest sticks out in front and your butt sticks out in back, like an s-curve. The best way to correct this tendency is to gently drop your tailbone down, and simultaneously imagine a thread pulling you upright from the top of your head. This double move automatically helps you straighten up and engage your core muscles to support your posture.
• While in a bent-knee position, such as a squat, your knees go past your toes; this can set you up for knee problems later. Modify the exercise so you can keep your knees over your ankles or toes.

Whenever you’re learning a new exercise, be sure you’re learning it correctly. If you can, work out with a trainer the first few times. If no trainer is available, practice the exercises at home using a big mirror to check your form. Even better, learn the exercise with a friend and you can check each other’s form. Whether you begin at home or at a park, focus on the quality of your movement rather than merely on the quantity of repetitions. I’d rather you did three slow, correct push-ups or squats than 25 fast ones using poor form. Start with one if that’s all you can do correctly and build up gradually to more (perfect) repetitions.