The front crawl, or freestyle stroke, is an efficient, popular stroke that swimmers use for racing, fitness and recreation. USA Swimming defines this stroke as "alternate stroking of the arms over the surface of the water surface and an alternating (up-and-down) flutter kick."

The handlebars on a bicycle serve two purposes: steering and support. Loose handlebars are dangerous because they make it hard to turn properly and will not support your body weight, increasing the likelihood of an accident. There are two locations where your handlebars can loosen: on the stem and headset.

All levels of organized soccer use the same types of markings, on field sizes of varying sizes. Markings on the field tell the players and referees when the ball is in bounds or out, and where the goalie can use her hands.

Swimming is a demanding cardiovascular activity that burns a high number of calories. Half an hour of vigorous lap swimming burns between 300 and 444 calories, while crawl and butterfly can burn close on 500 calories in the same amount of time.

Baseball requires a high degree of skill to play well. Athletic ability will help a player compete with other top players, but the specific skills of hitting, throwing and catching the baseball require significant work and practice to acquire.

Whether a basketball player remains calm or experiences performance jitters depends on how effectively he responds emotionally to daily situations when something is at stake.

Even if you don't play volleyball competitively, casual play in the backyard or on a beach requires athleticism. Jumping and running, as well as serving and spiking the ball, all require strong muscles and flexible joints.

Cycling is a low-impact exercise, and those who actively participate in cycling have about 10 percent more leg muscle than those who refrain from exercise, according to the Chester Knee Clinic & Cartilage Repair Centre.

Soccer drills for 6- and 7-year-olds help to improve their dribbling, scoring and passing skills. Drills also help develop teamwork and communication skills for each of your young players, which can improve team chemistry and their ability to win games.

Chlorine is a yellow-green gas with a strong odor that ranks among the top 10 most common chemicals produced in the United States, as of 2011. Used during World War I as a chemical weapon, today its uses include disinfecting everything from tap water to industrial waste and sewage.

Basketball can be a healthy activity, one that increases stamina, strength and coordination while also promoting teamwork. Like any sport however, basketball has its disadvantages.

Shimano makes a variety of bicycle parts, including the XT rear derailleur. A rear derailleur is a spring-tension mechanism attached to the bike frame near the back wheel. It is part of the drivetrain and is necessary for your bike to shift gears.