Heidi Klum, the fashion model and host of the popular television show Project Runway is famous for saying, "You're either in or you're out." She may not be referring to the weather, but the phrase certainly defines the season we are in.

During this time of year in Central Texas the weather can change drastically in a matter of hours and that can have a major impact on your workout plans. Rather than cancel the workout or try to play weather predictor, planning for both scenarios -- an outdoor workout if the weather is nice or an indoor workout if the weather turns dismal -- will allow you to maintain your routine. "Variety is good for an exercise program," says Mark Langendorf, Exercise Specialist Cardiac Rehabilitation at Seton Medical Center Austin.

Daily Exercise Requirements

Experts usually recommend either of the following types of exercise:

• Activity at moderate intensity (equal to a brisk walk) for 30 minutes a day, five days a week or more.

• Vigorous exercise for 20 minutes a day, three times a week or more. (Vigorous exercise is done at a pace that increases your heart rate to 70% or more of your maximum heart rate. Your maximum heart rate is the fastest your heart can beat at a maximum activity level. To find your target heart rate for exercising, use the target heart rate calculator.)

Children and teens should be active at least one hour a day. Activity should be of at least moderate intensity. Walking briskly is an example of a moderate activity.

Generally, fitness professionals recommend three types of fitness training: aerobic, muscular and flexibility. Core stabilization and balance (strengthening the abdomen, hips and lower back) can be included in the muscular category or pulled out as separate training. When creating an exercise program, make sure you include diet and nutrition to optimize healthy living.

In or Out

If your mind is dead set on doing the activity you've scheduled, then you'll need to plan to go indoors if the weather turns inclement. AustinFit Magazine broke down the differences between fitness training outdoors and indoors.

When it comes time to burn some calories, do you hit the gym or hit the pavement? Both options have their pros and cons, but there may be some factors you haven't considered. Here's a rundown of three favorite workouts that will keep you slim in or out of the gym.

Trail or Treadmill

Running or walking on a treadmill may keep you dry, but you won't get the same kind of challenge you would on natural terrain. For one thing, the surface of a treadmill remains constant, regardless of any incline you add, whereas running on pavement or a grassy hill provides a wide range of surfaces that work your muscles whether you realize it or not. Some people prefer the treadmill because it allows them to control the variables and monitor their progress at all times, as well as zone out to their favorite sitcom or the latest news story. While this may be a motivator for some-- particularly older people who don't want to brave the elements -- studies suggest that walking outdoors is an all-around healthier option because it stimulates the mind as well as the body. Serious athletes also swear by the pavement when they're training. After all, marathons aren't run on a treadmill.

Spin or Cycle

Until a couple years ago, taking your bike ride outdoors definitely had the leg up in this comparison. But with the soaring popularity of "spinning," a high-energy indoor cycling workout set to music, it seems there may be a tie. Certainly, there's something to be said for hitting the hills on a road bike -- the fresh air, the scenery, the adrenaline rush you get flying downhill after pushing your way up a steep climb -- but "spinning" definitely takes indoor cycling to a whole new level. In fact, during a one-hour class you're likely to burn more calories than you would going for a 60-minute bike ride, mostly because there's an instructor to encourage and challenge you the entire time. if you still can't decide between these two options, we suggest a little of both. Spin your heart out during the week, and then when the weekend rolls around, take your bike out for a leisurely ride.

Lake It or Fake It

For many people, a stationary rower is a lot more accessible than a canoe or skull, and unless you're on a crew team or an avid kayaker, you probably don't need to worry about weighing the two options. Even so, it may be to your advantage to try out the real thing for a change of pace and scenery. The problem with stationary rowers is that most people don't use them correctly, putting too much emphasis on pulling with the upper body. Rowing is actually a lot more about engaging the core muscles and the lower body than working the arms. If you know what you're doing, the stationary option can be used as a good training tool, but just think how much more fun you'll have skimming across the lake, taking in the sights and sounds while you row, and working your body from head to toe.

Workout Environment Pros and Cons

With any environment there will be something you give up in order to get the workout in. For example, you may have to run early in the morning while it's dark in order to take advantage of cooler temperatures. While not everything will come together to provide the optimum conditions, there are a few things to look at when making a decision to go inside or out.

Inside

Pro: "A successful program requires a structured environment to establish or re-establish exercise behaviors," says Mark. Indoor exercise environments are more easily regulated. The temperature and light can be adjusted. Television sets can be turned on or off."

Pro: Working out with others indoors at a gym provides the social opportunity of meeting others. By watching others working out you may be able to learn new exercises or techniques.

Con: Home and Gym workouts can be distracting. If you don't turn off the phones, the television, the fax machine and all other electronic devices they will eventually call for your attention. Other family or gym members may not respect your need for privacy. Whether it others chatting about local news or gossip or the kids needing your attention, interruptions can cut a workout short creating frustration and stress rather than positive feelings.

Outside

Pro: There is more to experience outdoors. Nature, whether it's falling leaves, bird sounds or a babbling brook, you get to enjoy it with all of your senses. Even if you live in an urban setting, there's always more to see and hear than indoors.

Pro: Exercising outdoors allows you to escape with just yourself and your thoughts.

Con: Choosing the proper clothing for the weather is a burden for many of the months. Carrying jackets during a run or bike outing can be an annoyance. Extreme temperatures also require more time for the body to get readjusted once the workout is over.

When the Weather Won't Cooperate

Be flexible with your workout plans and consider some alternatives. You might not be able to run eight miles but if you choose one of these options, you won't be sitting on the couch either. Here are some ideas to help attain at least minimum exercise.

• This time of year a workout can always be substituted with holiday shopping. A brisk 30-minute walk through the mall will not only meet the minimum exercise requirements for the day, it'll also allow you to get a jump start on holiday shopping.

• Grocery shop. Grocery shopping burns as many calories as slow ballroom dancing or bowling.

• You don't need a full gym in your house but having a couple of dumbbells, an exercise band or a stability ball will not take up much room and allow you to quickly get in a workout if the weather is too extreme to venture out.

• Pop in to a fitness club for a single day pass. Many clubs in town offer a single day pass for less than $10. So for the cost of a movie at the theatre, you can have access to all the fitness club amenities for the day. You may find that you'll really take advantage of the pass and extend the length of time of your workout.

• All exercise routines can benefit from a stable core. Using only your body as resistance, a complete workout can be created just by using your own weight as resistance.

Whether you choose to workout indoors or outdoors, the most important point to remember is that YOU ARE working out. You've chosen motion over stillness. Although your brain may be disappointed you didn't get to see Lady Bird Lake this afternoon, your legs won't know the difference between the lake and the mall and will reward you with good health for just moving.