Water skiing is a sport that combines the grace and power of alpine skiing with the acrobatic flair of gymnastics and aerial skiing. Water skiing, the action of pulling a skier across a body of water by a motor boat, was invented by American Ralph Samuelson (1903–1977) in Minnesota in 1922. In its early period, the sport of water skiing was limited to the simple demonstration of balance by the athlete as they were transported across the water. With the development of increasingly powerful motorboats, water skiers could be pulled at significantly greater higher speeds. As skier speeds increased, water skiing expanded to include three distinct components—slalom skiing, where the skier navigates through a series of buoys set at irregular intervals on the water, creating obstacles similar to the gates used in Alpine slalom skiing; trick skiing, including the use of a single ski, barefoot skiing, and different types of acrobatic tricks; ski jumping, where the skier is pulled by a tow boat towards a ramp that is approximately 21 ft (6.5 m) long and 6 ft high (1.8 m); the ramp is anchored in a fixed position in the water. The winning jump in competition is determined by the distance achieved by the skiers, as there are no marks awarded for style or form. Elite water ski jumpers can attain distances of over 150 ft (45 m) in the air.
From its creation in the United States, water skiing was introduced to parts of Europe; it gained a particular popularity in areas such as the French Riviera. The International Water Ski Federation (IWSF) was founded in 1949. Today, water skiing is popular in all countries that possess access to any significant bodies of water. The IWSF sponsors a World Cup water ski tour that attracts professional competitors. The IWSF is a member of the Olympic movement; water skiing is not an Olympic sport.
The IWSF is also the governing body for the related sports of wakeboarding and kneeboarding. A wakeboard is a device with a construction similar to that of a snowboard, and the sport incorporates elements of surfing, snowboarding, ice skating, and waterskiing. As the name suggests, the wakeboarder rides in the wake generated by the towing motorboat; a knee boarder is positioned on their knees. Each discipline is particularly suited to the performance of tricks, including high speed turns, and a variety of somersaults and flip movements.
In water skiing, the prospective skier is generally introduced to the sport through the use of two skis. Once the skier establishes the desired degree of balance and proficiency, the skier will often develop further skills using a single ski, particularly in the execution of more demanding turns and slalom techniques.
The basic principle of physics that explain how the water skier is kept afloat while being towed is the same principle involved in the motion of the boat itself across the water. Planing is the application of the physical law that provides that all action will produce an equal and opposite reaction. With the water ski, designed with the ski tip tilted slightly upwards from the surface of the water, the water strikes the ski as the skier moves forward, creating a rebound downward from the ski. The rebound creates an upward force on the ski and the skier. So long as the upward water force is equal to the downward force of gravity (the weight of the skier), the skier must remain afloat.
When the skier is traveling in a straight line behind the boat, the two forces acting upon the skier are the force of the tow rope, as created by the movement of the tow boat, and the force of the water upon the skis. Assuming a constant tension in the tow rope, the skier will travel at the same speed as the boat when positioned directly behind the boat. When the skier endeavors to move in a perpendicular direction from the path of the tow boat (across the wake, the wave turbulence produced on the water's surface by the boat and its engine), a centripetal force is added to those forces directed against the skier.
Centripetal force means to "seek the center." The skier who moves in a path perpendicular to the direction of boat travel will be subjected to a force that produces acceleration upon the body of the skier toward to the center of the circular path, which is the boat. It is for this reason that the skier can move faster than the tow boat when all three forces acting upon the skier are combined.
Water skiers often travel at speeds in excess of 50 mph (80 km/h) if the tow boat is sufficiently powerful. If the skier falls at such speeds, the force of the impact into the water can cause significant injury.
The equipment used by water skiers in competition is regulated by the IWSF. The skis may be manufactured from wood, metal, or composite material products. Skis may not exceed 39.3 in (1 m) in length, with a maximum width of 9.75 in (25 cm). In cooler temperatures, most water skiers wear a full body wetsuit, which provides insulation to the skier as well as a degree of cushioning in a fall. A sleek, form-fitting life jacket is also mandatory.
The most common water ski injury are those sustained to the lower legs, including the knee joint. Research has established that 35% of water ski injuries occur in the lower extremities, with one half of those injuries sustained to the knee. The execution of high speed jumps and twisting movements directs significant and often irregular forces into the knee, as do the high speed falls that create awkward angles of collision between the water skier's body and the water surface.
Strength and conditioning exercises for water skiing are directed to both physical performance and the reduction of injuries. Skier leg strength is developed through exercises such as lunges or squats that assist in maintaining an appropriate strength ratio between the two sets of muscles that govern knee flexion and extension, the hamstrings and the quadriceps. A 3:2 ratio in the relative strength of the quadriceps to the hamstrings is generally accepted as one that will ensure balance in knee movement. Exercises such as calf raises develop the gastrocnemius and soleus muscles (the calf muscles) of the lower leg, which are important to maintain the skier's balance on the water.
As with many sports where the athlete operates in the air, as with a water ski trick or jump, the development of the skier's balance and perception skills is vital to competitive success. A Swiss ball is an effective tool for these purposes, as the skier can replicate many water ski movements and sensations through balance exercises with the Swiss ball; in essence, these exercises permit the skier to practice at being stable in a variety of positions.
Large muscle mass is not an essential aspect of water skiing. High repetition/low resistance weight exercises, designed to promote a well balanced physique, are an important part of the comprehensive dry land training of the water skier.