Who hasn't wanted a tighter butt? Or a set of abs that are actually visible? Or arms that are high on tone and low on jiggle?

People ask constantly about how they can tighten or improve the appearance of one or two specific body parts, said Dan Kelly, fitness director at the White Bear Lake Lifetime Fitness. But spot-toning just doesn't work.

"In 90 percent of the cases, it becomes about losing body fat," Kelly said. "If I wanted to get abs and get my abs to show through, then doing a thousand crunches a day will build muscle underneath, but you won't see results if you're not shedding some body fat through proper nutrition and cardiovascular activity."

Fortunately, many outdoor summer activities can improve your cardiovascular system and overall fitness, which will help those beautiful abs and buns shine through.

"Doing multiple activities outdoors is, in my eyes, the ultimate cross training," Kelly said.

Although true health requires a balanced approach to caring for your whole body, different activities do activate and emphasize different parts of the body. So if you're just dying to buff up your shoulders for tank top season, you'll want to opt for kayaking instead of running.

But be sure you're doing your activity of choice strenuously enough to get a true cardiovascular workout, cautioned Stacy Ingraham, an exercise physiologist at the University of Minnesota. Pedaling leisurely on your bike with Fluffy the poodle perched in your front basket won't do the trick.

Most people need to get their heart rate up to at least 140 beats per minute, depending on their health and fitness levels, Ingraham said. Another way to improve cardiovascular fitness is to do intervals by alternating between going hard for a period of time and easy for the next period. Or incorporate hill repeats into your workout.

Whatever activities become a part of your routine this summer, remember that it might be worth it to learn from a fitness professional to make sure you're doing things properly. That'll reduce your chances of injury or burnout and increase your efficiency and chances of sticking with a workout. Read on to learn which activities work certain body parts more than others.

ROWING

Body parts: Naturally, your arms and shoulders get stronger from all that pulling and pushing, but rowing is also an excellent workout for your glutes (butt muscles), quads and hamstrings. Rowing works those muscles in a way that's similar to a horizontal squat machine. In addition, the core (abs and back) is strengthened as it works to stabilize the rotating body through each stroke.

Getting started: Take a look at the Minnesota Rowing Foundation's website, www.mnrf.org, to find a club and lessons near you.

BIKING

Body parts: The quads are the powerhouse when it comes to cycling, and glutes, hamstrings and calves also get stronger. Riding uphill, or riding uphill while standing on the bike, will work the lower body especially hard. Also, if you're positioned in a way that has you leaning forward on your bike, you're likely to be engaging your deltoids (shoulder muscles), chest muscles and triceps.

Getting started: Visit a bike shop for a proper fit and suggestions on safe places to ride. Check out bike trails statewide at www.mntrails.com.

CANOEING AND KAYAKING

Body parts: Chest muscles and biceps will engage as you lift and pull the oar, and the muscles in your core get strengthened as you switch sides.

Getting started: See www.exploreminnesota.com/experiences/outdoors/water for information on canoe and kayak rental.

RUNNING

Body parts: Running is a major workout for the lower body -- quads, glutes, hamstrings and calves are all involved. But running also requires strong support from the core, so your hips, abs and back muscles get stronger, too. As the arms rotate back and forth, your deltoids, biceps and triceps can get a little boost, too. If you want to emphasize the lower body, and especially the calves, try running sprints or hill repeats.

Getting started: Visit a nearby running store to get fitted with shoes, learn routes or join a club with group runs. See www.raceberryjam.com for information on upcoming races.

SWIMMING

Body parts: Swimming works almost every muscle group. Any stroke that has you turning from side to side uses rotator muscles in the core and shoulders. As you lift and pull with your arms, you'll strengthen shoulder and arm muscles. Once your hand hits the water and you pull back, you'll use back muscles. And if you do a variety of strokes with different kicking styles, you'll firm up your glutes, quads, hamstrings, calves, inner thighs and outer thighs.

Getting started: Many swimming schools, community centers and athletic clubs offer group or private lessons for adults. Take some classes and then head to a lake or pool to perfect your stroke.

INLINE SKATING

Body parts: This needs to be done at a pretty high speed in order to achieve a cardiovascular workout, so be careful where you skate. At a high speed or up hills, it's a great workout for the inner and outer thighs, quads and glutes. It'll also work your upper body and core as those muscles keep you balanced.

Getting started: See www.robichones.com to learn and www.skateminnesota.com to get involved with the skating community.

CLIMBING

Body parts: This is a major workout for the upper body as you pull your body upward using your shoulders and arms. But using only the upper body will lead to burnout. Proper climbing makes use of the hips, glutes and legs, which stabilize and drive you to the next position.

Getting started: See www.vertical endeavors.com for a place to learn and practice climbing.

Sarah Moran is a freelance health writer in Minneapolis.