Despite its scientific pedigree, cross- training is just a spiffy word for mixing up your exercises. The best way to achieve solid weight loss and sound fitness while remaining a grip on your sanity.

If you want to gain all the benefits of exercise, and there are lots of them: strength, endurance, health, a lean look, you’ll have a much better chance of covering all the bases by doing different activities.

The term cross-training is often defined as combining different types of exercise: for example, stretching, aerobic, and resistance exercises. But any time you mix up your workouts – cycling plus running plus speed walking, for instance – you’re cross-training.

Cross-training isn’t complicated. You can do it simply and effectively without a personal trainer or without a pair of sneakers so expensive that they out to speak four languages and do your taxes. More important, it has wide ranging benefits.

Mixing up your exercises brings more muscles into play. This will make you stronger and less prone to injury and few people lose weight nursing a muscle pull. The whole body muscle zap will make you look better, too, enabling you to avoid the fun house mirror look of the zealous cyclist with Terminator thighs and a taffy torso.

From a practical standpoint, cross-training provides you with more options and fewer excuses. Pool closed? Go for a run. Run snuffed ny a fresh dump of snow? Grab the cross-country skis. Stuck in a strange city whose traffic is outdone only by the crime rate? Bang out some calisthenics in your hotel room.

If your goal is to get lean while enjoying a tremendous range of exercises, sports, and workout times, then cross-training is definitely for you. If you want to build a sound fitness base and burn fat, cross training works very well.

The Aerobic Attack

With the exception of steering clear of onion rings, snack cakes, and other high-fat (and fattening) foods, the most efficient way to excise surplus calories is with regular aerobic exercise. By alternating among a variety of aerobic choices, everything from cycling and swimming to in-line skating, you’ll whip your heart and lungs into shape, while at the same time working (and balancing) muscles in every part of your body.

Think Big – It’s a simple rule, so it should be easy to remember: The more muscles involved in an exercise, the more calories burned. When you’re looking to burn fat, go after the big muscle groups – the kind you work by running, swimming, cycling, cross-country skiing, rowing, tennis, basketball, and so on. Table tennis certainly has its intrinsic values, but unless you’re a member of the Chinese national team, weight loss isn’t one of them.

Start Early – You don’t have to be a seasoned athlete to take up cross-training. It’s also a superb way to ease back into shape. Mixing up exercises eases the initial shock to unfit muscles. Start a fitness program with running only, and you put a lot of repetitive stress on some pretty fragile muscles like the calves and achilles tendons. But if you run one day and bike the next, your calves and hamstrings get a rest on cycling days, and your quadriceps get a break when you run.

Better yet, get off your feet entirely. Alternate running or biking with a day of swimming. It’s not only great exercise but it’s also a wonderful liquid balm the day after a bike ride or run, stretching out the muscles and freeing them from the stress of gravity.

Mix it up Slowly – It’s a painful scenario: A long time cyclist decides to do some running. He sets off hard. Calf muscle makes a sound like the peeling away of Velcro. Cyclist spends many weeks rehabilitating.

Whether you have started exercising or have been buffing your butt for longer than you care to admit, it’s critical to take up new exercise slowly. Even if your heart and lungs aren’t the limiting factor, your muscles and tendons are, and if you don’t coddle them, you’ll have problems.

If you’re coming back from time off or you’re starting something new, going straight into hard effort will set you up for a tendon or ligament injury. You’ll have better results if you’re patient and build things slowly.

When you’re taking up a new sport, no hard effort for at least four to six weeks. In the meantime, take it slow and easy. Build endurance and condition the muscles first. Don’t worry about speed, just go slow and have fun.

Split Up the Workouts – There’s a male mystique that says you always have to finish what you start. If today is your running day, you run. When you start on the exercise bike, you finish on the bike. While this sort of single-track thinking may get you through business school, it isn’t as productive when it comes to aerobic exercise.

You can sidestep fatigue to a degree by doing two different aerobic exercises during the same workout. Shifting the onus to a different set of muscles in mid-workout will let you push harder just a bit longer, and pushing harder helps maintain a higher calorie burn.

Calorie burn varies from person to person, but generally if you spend 15 minutes on the treadmill exercising at 70 percent of your maximum ability, and then hop to the cross-country ski machine for 15 minutes at the same intensity, you’ll burn roughly a third more calories than you would if you ran on the treadmill at 50 percent effort for 30 minutes.

You might not be able to sustain that effort every time just because you switch activities, but as a rule you will be able to benefit both psychologically and physiologically by changing things up.

The same mix-it-up approach can be applied outside the club as well. Run to the pool. Or toss a pair of in-line skates into your backpack, ride your bike for 15 minutes, then hop off and skate.

Do Workouts Within Workouts – Technically, cross-training involves the mixing of different sports and exercises at different times. But we’ll be creative for a moment and suggest that we mix things all at the same time.

Remember, the more muscles you involve in your exercise or the more you tax those muscles, the more calories you’ll burn. So innovate. Carrying a pair of 3-pound dumbbells as you run can increase the amount of calories burned by as much as 20 percent. Wear swim fins in the pool; it will make those big, oxygen-hungry muscles in your legs work harder and gobble up more calories.

Obviously, you don’t want to take this too far. Using dumbbells while riding a bike will likely bring trouble, but the only limit is the limit of your imagination. It doesn’t take big changes to get results.

Location, Location, Location – If you take up a sport that can only be done in a fitness park across town and only between the hours of 5:00 and 6:00am, you won’t be doing it long. It has to be convenient so that you’ll do it. If you have to drive 15 miles across town to exercise, you’re not going to do it.

Be Reasonable – Cross-training is the best route to well rounded fitness, but this doesn’t mean that you should take up an exercise routine that requires its own appointment book. The sporting goods industry would certainly like it if we all incorporated boxing, volleyball, running, cycling, aerobic dance, and judo into our exercise week, but this is neither practical nor wise. You need to engage in a specific exercise with some regularity.

Why? Because repetition brings conditioning. If you’re only running once every two weeks, you’ll be starting almost from scratch each time, and you’ll certainly never get in good enough condition to work hard enough to burn serious calories.

Though this isn’t written in stone, experts generally advise picking two aerobic exercises that you like and then mixing them through the week. Cycling on Monday, Wednesday, and Friday and running on Tuesday, Thursday, and Saturday (because each exercise stresses different muscles, alternating them like this gives those muscles a day off to recover).

Building Muscles

That weight training could be used to lose weight might seem ludicrous, since even recreational lifters add bulk to their frames, and serious lifters look like sides of beef. But experts have found that weight training is an extremely effective tool in the battle to burn fat, particularly when combined with aerobic workouts.

Though sorely outnumbered on most of our frames, muscle cells are far more metabolically active than fat cells. A pound of muscle can require 35 to 45 more calories just to get through the day.  Adding more muscle to your frame actually helps burn fat more effectively throughout the day. Particularly when combined with aerobic workouts, cross-training in the weight room works a larger variety of muscles than by doing the same lifts over and over again. That means existing muscle cells grow, and that, of course, means more fat burned.

When you’re trying to lose weight, experts say, it’s a good idea to combine three days a week of aerobic exercise with two days of weight training. While two days of weight training isn’t enough to promote substantial strength gains, it’s more than enough to provide muscle mass to achieve the metabolic burn that you’re looking for.

Work the Big Groups – If you spend much time in the gym, you’ve almost certainly seen the big guys spending what seems like an inordinate amount of time working on small parts of their anatomy, doing wrist curls or heel raises. But when you’re trying to lose weight, doing isolated dumbbell curls isn’t your best bet. Instead, focus on lifts that hit big muscles and big groups of muscles. The more muscles and joints involved in a lift, the more caloric expenditure.

There are lots of these big muscle groups to work on. Doing lunges, for example, works the quads, and hamstrings; bench presses are good for building the chest, shoulders, and triceps.

Do the Circuit – A great way to combine lifting with aerobic exercise is circuit training. It works like this: Select six to eight big-muscle lifts that will give your whole body a workout. Do 12 to 15 repetitions of each exercise. Rest 30 seconds between exercises. After you have done all the exercises, rest for up to 2 minutes, then repeat the circuit again.

Lifting this way drives the cardiovascular system to a higher level and then keeps it there because you don’t allow enough time for recovery. Because, your cardiovascular system is elevated, you’re burning more calories.

When doing circuit training, you’ll want to substantially reduce the weights that you normally lift. As a rule, plan on lifting 40 to 60 percent of your current max. If you’re new to weight training, you’ll want to build a strength base first: three days a week of lifting for two to three months should do it.

Stand and Move – To boost the calorie burn just a little more, concentrate on standing lifts. For example, do standing dumbbells military presses as opposed to those performed seated. Standing lifts burn slightly more calories because you are working to support your own weight too. Add some movement to those standing lifts by doing lunges instead of taking a seat on the leg extension machine and you’ll up the caloric burn again.