What is the best method to burn fat and calories: a high-intensity workout or a lower-intensity workout that lasts longer?

Proportionately, you'll burn more fat by exercising at a slower pace fora  longer time.  However,  the total amount of fat and calories you burn will be lower in a lesss intense workout.  To effectively burn fat and calories, you need to combine time and intensity to your workout routine.  Remember, it takes a deficit of 3,500 calories to burn one pound of fat!  Here are a few tips to incorporate greater intensity to your workouts:

• Use interval training.  Run hard for 1 minute and easily for 2.
• Use hills and steps.  Push your intensity up the hill annd recover on the return trip down.
• Use your local track.  Sprint the straighaways and jog or walk the turns. 

This doesn't mean you should forsake low-intensity workouts.  Far from it.  Mix up your workouts throughout the week: One day is a slow-jog session, and another day is a stair-training workout.

Why is stretching important? Should I stretch before and after my workouts, or just after?

Well, the jury is still out, and the research is inconclusive.  Some research has indicated it can decrease power in your muscles.  Many people, including myself, believe in stretching major muscles after a good warm-up, but some researchers feel it could be counterproductive because your heart rate drops.  I say, so what? Just build it back up again.  All experts agree that we should stretch after out workouts.  It's the most productive and safest time because the muscles are warm and pliable.

Here's a good rule of thumb: Warm up for 5 to 10 minutes.  If anything feels particularly tight, tlike your hip flexors, hamstrings, quadriceps, or calves, stop and stretch them.  And always strech after your workouts.  You'll prevent injuries and feel great.

Tips to remember:

• Never stretch a cold muscle.  Always warm-up for at least 5 to 10 minutes before stretching.  On chilly days, extend this warm-up to 15 or more minutes.
• For best results, activate teh Golgi tendon organ (GTO): Hold a stretch for 5 seconds, release for 5 seconds, and then execute the stretch again.
• Hold a stretch for 20 to 30 seconds, or for a total of three diaphragmatic breaths.
• Inhale to prepare for a stretch and exhale slowly while lengthening the muscle. 
• Outdoors, be well aligned and evenly balanced on your terrain. 

I live in a large city where the air pollution can get really bad.  Should I be worried about breathing that dirty air?

Air quality is a concern for everyone.  Exercising outdoors in some cities may put people at a greater risk for compllications from frequent exposure to ozone than for those who do not.  Ozone is pollution formed from the emissions of cars and trucks, wood-burning stoves, chemical or industrial plants, and refineries.  These pollutants have a chemical reation to heat and sunlight.  Exposure to ozone can irritate the respiratory system and aggravate asthma.

If you believe the air quality is suspect, take precautions.  The U.S. Environmental Protection Agency (EPA) has produced an Air Quality Index (AQI) to make it easy to understand the current air-quality conditions.  The index has a range from zero to 500; the higher the value, the higher the level of air pollution in the atmosphere.  Anything above 150 is considered unhealthy.

Find out the AQI in your city by listening to local forecasts or by logging on to the EPA Web site at www.epa.gov.

By the way, if outdoor poluution and ozone seem a little unnerving, consider the following information from the EPA:

Indoor air levls of many pollutants may be two to five times, and occasionally, more than 100 times higher than outdoor levels.  Indoor air pollutants are of particular concern because most people spend as much as 90 percent of their time indoors.

Tina Vindum is the founder and president of Outdoor Fitness. She is the author of Tina Vindum's Outdoor Fitness: Step Out of the Gym into the BEST Shape of Your Life (FalconGuides, 2009), from which this column was excerpted. Vindum hosts a national weekly radio show on Outdoor Fitness and lectures internationally about its benefits. Her work has been featured in Self, Fitness, Prevention, Sports Illustrated for Women, Backpacker, Vogue, the New York Times, and the Los Angeles Times. She lives in San Francisco, California.