If you want to be fit, three things are critical to your success: eat well, tone your muscles and do cardiovascular workouts.

“If you’re missing any one of these three things, your body will not reach the full potential that it could,” said fitness trainer Stephanie Granzow.

While all of these are important, cardiovascular workouts are vital because they also protect against health risks, such as heart attack, stroke, diabetes and high blood pressure, by conditioning the heart. And because you burn calories when exercising, you also can lose weight, which lowers disease risk.

But if you’re like most people, getting in those cardiovascular workouts is downright difficult. Fortunately, most health facilities have many pieces of equipment to choose from.

Treadmills, elliptical trainers, step machines and stationary bikes are great, but exercisers should know how to use each correctly to avoid repetitive use injuries, said Matt Bartz, athletic director at Le Club in Milwaukee.

Even exercising correctly on aerobic conditioning machines can cause problems if you do too much, he added.

Bartz, a certified strength and conditioning specialist with the National Strength and Conditioning Association, said that companies “make machines as user-friendly as possible.” But if a movement feels awkward or uncomfortable, users should seek help from staff at the gym.

He said the treadmill is “probably the most-used piece of cardiovascular equipment at any fitness center,” but that it is also the piece exercisers are most apt to get injured on because it’s constantly moving. He stresses that exercisers should not only know how to use treadmills correctly, they should also know how to use the safety features.

Another way to ensure safety is to use different types of machines. Using just one machine increases injury risk because the same muscle groups are used the same way each time, Bartz said.

“You may be OK for a while, but as you increase in intensity and duration, you will have a higher chance of getting hurt. Usually everyone can find at least two cardio workouts that they can do. You should try a few different motions. Cross-training is a friend, and it’s a good way to keep you healthy,” he said.

Bartz added that one of the best ways to use the machines – for advanced exercisers – is to try the interval training settings.

These workouts give “certain ratios of working harder, then easier. There are all sorts of intervals you can do. Interval training is a great way to safely and gradually increase your fitness level.”

Granzow, who is certified by the International Sports and Science Association, said exercisers should do cardio workouts three to five times a week “for a very baseline minimum of 20 to 30 minutes.”

For most people, exercising three times a week will help maintain their fitness level, but four or five workouts a week will improve it. While doing these workouts, it’s important for people to monitor their heart rate and to work within a zone that is safe for their fitness level and age.

ELLIPTICAL TRAINER

Primary muscle groups worked: quadriceps, hamstrings and glutes.

Put your foot on the lowest pedal first. Then hold on to the handrail and step onto the other pedal.

Position your body forward with the majority of your foot on the platform. Keep your feet straight; don’t let them bow in or out, don’t let them hang off the platforms excessively and don’t press them up against the very front of the pedal – this may cause numbness in the feet. Don’t let your knees bow out – they should be in a straight line with your feet.

Stand straight in a neutral spine position, keeping core muscles tight. Don’t lean forward unless you’re on equipment that gives you advanced options that instruct you to lean forward.

While moving, concentrate on pressing your heels down slightly on the downstroke. You can use a light grip for balance, if needed. Once you are more advanced, you can start pumping your arms.

On machines that give upper bodies a workout, use a grip with a slight bend in your elbows. Don’t overextend your arms and shoulders.

Keep bouncing to a minimum. It’s OK to go for speed, but don’t throw your body around. Excessive bouncing often means the individual is using too little resistance.

STATIONARY BIKE

Primary muscle groups worked: quadriceps, hamstrings and glutes.

Adjust the seat so it is roughly at your hip level when standing next to it. Place one foot on the lowest pedal, then put your other foot onto the higher pedal. Do a few revolutions to make sure that when your leg extends, your knees are just slightly flexed at the bottom of the stroke.

Sit up straight, keeping a neutral spine position. Keep your back flat and core muscles tight.

It’s all right to lean forward if you want to stretch your back, as long as you are able to keep your back flat and your core muscles engaged. If your back starts to round, correct your form immediately as this can cause pain or tightness in the neck area, even soreness in the lower back.

Hold on to the handlebars very gently with wrists in a neutral position – don’t flex them.

TREADMILL

Primary muscle groups worked: quadriceps, hamstrings, calves and glutes.

Start with your feet on the non-moving side rails and set the controls at the lowest rate of speed and incline. Step onto the pad and start walking slowly, using a heel to toe movement. Try to keep your gait as natural as possible.

Keep a good posture by standing straight with your eyes forward, chest up, shoulders back. You should be in a neutral spine position, with your core muscles engaged.

If you’re new to treadmills, lightly hold onto the side bars. Once you’re comfortable with the machine, pump your arms while walking, but keep your hands relaxed. Arms should be bent at a 90-degree angle.

When you’re ready to increase intensity, do it gradually.

Don’t turn and talk to people while on the treadmill because you may inadvertently turn your body in that direction and fall off the machine.

Don’t put your machine on a high incline then hold onto the front bar to take tension off your legs, since they’re supposed to be doing the work. If you have to support yourself in this manner, you’re likely going too fast.