GEAR AND GADGETS : Keeping Fitness Programs on Track When You’re On the Road : Portable weights, exercise belts and heart-rate monitors fit easily into luggage.

While many vacationers put their customary fitness routine onhold when they leave home, others resolutely incorporate exercise into their travels.

Whether it’s a daily jog through a European park, a stint in a hotel pool or gym, or calisthenics in the room, health buffs find ways to work out on the go. A broad range of products that travel easily can help them in that quest. (Prices do not include postage and handling.)

Weights are an integral part of most well-designed exercise programs, but who wants to schlep around a set of barbells? Travel Trainers are hollow vinyl pouches that can be filled with 1 to 3 pounds of water each; they then are wrapped around wrists, arms or ankles and secured by Velcro closures. Voila, weights. When empty, the trainers weigh only four ounces apiece and fold flat for packing.

I found Travel Trainers a helpful exercise aid. The feel of sloshing water was a bit disconcerting at times, and the movement of the water sometimes made the weights shift on my arm, but by and large, the concept worked well.

Travel Trainers (Item No. RA747) are $28.50 a pair from Magellan’s; tel. (800) 962-4943.

Working out can put a lot of strain on back muscles, and fitness experts often recommend wide weightlifting belts for lumbar support while training. This lightweight but sturdy neoprene belt has, as a bonus, an inside pouch that accommodates a small reusable heat or cold pack, sold separately. The heat pack, which helps warm up cold back muscles, is a plastic pouch filled with a nontoxic liquid that reacts with a chemical activated by a button in the pouch. The cold pack, good for soothing sore muscles, is filled with a gel that chills when placed in a freezer.

The belt pouch, which has a Velcro closure, also can be used for carrying small items such as locker or room keys, credit cards or paper money for, say, tips to a gym attendant or a cold drink after an outdoor run. Because the neoprene material is waterproof, the belt can be used for water aerobics, windsurfing and jet-skiing.

As someone with lower back problems, I found the Thermo Pro Exercise Belt a good travel alternative to heavier weightlifting belts. It did not provide quite as much lumbar support as a traditional weight belt made of stiff leather. For an easy-paced jog or a workout with light weights, however, it worked fine--and added only a few ounces to my luggage. Thermo Pro Exercise Belt, $30, is available in six bright colors and four unisex sizes. Reusable heat pack costs $7; reusable ice pack is $5. Package price for the belt with heat and ice packs is $40. The belt and packs are sold at sports retailers, or can be ordered directly from Thermo Pro; tel. (800) 438-3482.

Athletes know that the most effective way to achieve aerobic fitness is to exercise at an intensity level that puts sufficient--but not too much--stress on the heart. The Polar Pacer is a portable heart-rate monitor that lets you keep tabs on your pulse rate during exercise and warns you when you go above or below a preset target. It’s a convenient substitute for the monitoring method of taking a wrist or neck pulse with your finger.

A large wrist-monitor display picks up pulse transmissions from a wireless sensor worn on an elasticized chest band. The wrist monitor can be easily programmed to beep when you go above or below your target rate. The instruction manual shows how to calculate that rate based on age, sex and fitness, and provides a suggested program for conditioning and fat loss. The pacer is water-resistant and displays time of day, so it can double as a wristwatch.

This is a fine aid to aerobic exercise at home or while traveling. It’s the perfect accessory for a spa vacation; while others in your aerobics class have to stop and take their pulse manually during a workout, you merely have to glance at your wrist to keep tabs, without missing a beat.

The Polar Pacer is $159 from Polar CIC, Inc.; tel. (800) 227-1314. The Polar Edge model, which also has a stopwatch, costs $189.

Not every hotel room comes equipped with a bathroom scale--which may or may not be a welcome amenity when you’re trying to get away from it all. Those bent on keeping tabs on their weight wherever they roam might pack the battery-powered MiniScale (just 4 1/2 inches in diameter and 13 ounces) that also doubles as a digital, 24-hour alarm clock.

Standing a few inches from a wall (for balance), you step up on the scale with the ball of one foot, then step off when a beep indicates it has recorded your weight. I found the scale a bit hard to program at first--but then I have trouble with those programmable wristwatches. Once I got the hang of it, the alarm clock worked fine and the scale (unfortunately) gave accurate readings.

The MiniScale is $59.95 from Norix, a mail-order company; tel. (800) 569-3868.

Whenever I’m traveling, I like to take along a towel for drying off during workouts or after an impromptu swim while on seaside drives. But a good-sized cotton towel takes up a lot of space in my luggage and never seems to dry in time for packing.

The AquaTowl is made of a synthetic material called Viscose, which the manufacturer claims absorbs 10 times its weight in water and then wrings out over 90% of it, making for rapid drying. The towel, which looks like flannel, measures a generous 34 inches by 15 inches, but is only one-eighth-inch thick, so it takes up little packing space and weighs only a few ounces.

I found the AquaTowl a bit hard to get used to, since I was accustomed to the feel of a big, fluffy terry-cloth towel. Also, the towel became quite stiff when it dried. The manufacturer claims the towel softens with repeated wetting and wringing--much like chamois--after which it absorbs and dries better.

AquaTowl (Item No. TA458L) is $12.85 from Magellan’s; tel. (800) 962-4943. A smaller version, 27 inches by 10 inches (Item No. TA458N), is $6.85.