Water based activities constitute a source of popular recreation as well as skilled sport, and embrace an assortment of indoor and outdoor events. Locations include swimming and diving pools, rivers, marina, watersport centres, lakes, off-shore resorts and open seas. Of current indoor sports, swimming has a long tradition founded on military preparation; diving and water-polo are well established Olympic sports; while octopush – a form of hockey played underwater – is a comparatively recent innovation. Rowing and canoeing are both strenuous river sports, wild-water canoeing being the most robust form. Various surfing and skiing competitions have evolved from leisure pursuits, the inaugural water ski championships taking place in France in 1949 after the formation earlier that year of the International Water Ski Union. Wind surfing employs a sail on a surf-board, its proponents suffering frequent immersion. Sailing and yachting races have been expanded well beyond the traditional shorter distances, presenting novel hazards as well as challenges to participants.
In many of the newer water sports regular recreational participation requires expertise in craft handling as well as swimming proficiency, though particular activities may safely be enjoyed by non-swimmers if sensible precautions are taken. Surfers and water skiers, for example, can wear a secure life-belt but are still strongly advised to learn to swim. Hire facilities at most resorts make the water sports open to practically all-comers who seek the experience without necessarily any prior conditioning. Development of inland water facilities has meant that enthusiasm has progressed beyond the sporadic recreational participation on the coastline. Proliferation of motor boats on the waters has brought attendant risks of collision and increasing concern for traffic control. The British Water Ski Federation, for example, lays down procedures when more than one boat is on the same stretch of water.
Risk of death by drowning is omnipresent. Watersport fatalities were found to account for 43 per cent of total accidental recreational deaths in Scotland in one year (Moncur, 1973) and for 21 per cent in Japanese high school students, over an eight year period (Izeki, 1973). In most cases, these are avoidable through insistence on standard and sensible safety precautions and eschewing unfamiliar and dangerous waters. These rates are still relatively low when the vast numbers of recreational participants are considered, while fatality is rare in watersport competitions. Strains and sprains associated with the muscular effort of heavy repetitive anti-gravity work are not found since the body mass is buoyed up in the water. For this reason exercise in water is often recommended in sehabilitation for land sports. Competitive watersports produce low injury rates, the incidence being less than two per cent of all sports injuries in the study of Cramp-ton and Tubbs (1977). The injuries characteristic of a selection of outdoor watersports are now presented. The risks and injuries in diving and competitive swimming are covered in 0.
Proficiency in water skiing ranges from the baseline of the beginner to the tricks and stunts of the professional. Beginners commence with two skis, the standard size being 165cm long and 16.5cm wide with fins 20cm long by 7.5cm deep. Wider skis are needed for larger body builds and ideally their size is also adjusted for age and sex. Adjustable footpieces of moulded rubber retain the feet firmly in place during take-off and skiing but dislodge easily in emergencies. A wave-borne errant ski can however cause concussion if hitting the head of an individual who has fallen.
Initial skill acquisition can be enhanced by land drills prior to entering the water. These might include sitting in a squat position on skis, holding on to a rope and slowly standing erect while resisting the pull of the instructor at the other end. With suitable land drills and instruction most learners can ski for a distance on their first day without the frustrations and discomfort of frequent failures. In the start position great leg strength is required to hold the skis in position in front of the body with knees flexed. The quadriceps contract forcefully as the body rises, the adductors help keep skis parallel as the boat accelerates abruptly and the hamstrings prevent excessive forward pull. In consequence, novices are often stiff on the day following their early practices. Learners should be coached to immediately release the tow rope once balance is irretrievably lost to avoid being dragged along the water. Mild injuries mostly occur with beginners, so consideration and care on the driver’s part can help prevention.
Proficiency develops relatively quickly as the skier masters criss-crossing the wake. This allows greater velocities than the usual 40kmh_1 of the boat to be achieved. At this stage sharp turns of the boat should be avoided by the driver, especially while the skier is outside the wake. For providing the necessary abrupt acceleration at take-off and for towing adults an outboard motor of 50 to 75hp is best. The skier may then graduate to mono-ski by discarding the unwanted one in the water. A safer but more skilful manoeuvre is to start with one ski from standing in shallow water, so avoiding the danger of leaving floating skis unattended. The skier then progresses to using shoe skis or riding on discs and later to barefoot skiing where speeds of Bokmh-1 are reached by experts. The greater the speed the greater is the hazard, and the harder is the impact with the water on falling. Because of the greater speeds they employ, barefoot skiers need padded wet-suits, usually made to measure, for protection in falls on smooth waters.
Competitive water skiing may require contestants to ski between six buoys in a mono-ski slalom run, the speedboat entering and leaving through the gate buoys. Special muscular effort is demanded in rounding the buoys. This is achieved by combining the actions of arms, shoulder and back in drawing the rope handle towards the trunk and braking the ski with thigh and leg muscles by pushing its rear end outwards and leaning in to turn. Hitting the buoy at this point can result in abrasions, lacerations and rib fractures (Bass, 1971). On rounding the buoy, torsion injuries to the ankle may occur if the bindings slip or elbow and shoulder strains from longitudinal forces applied to the limbs if the rope slackens.
Alternatively, long distance competitions involve skiing out to sea and turning at a gate to return towards shore. Appreciable isometric strength and endurance in the arms, shoulders and legs is needed as well as balance. Speeds approaching lOOkmh-1 are common in internationals where the minimum race distance is 50 nautical miles (90km). The first buoy must be at least 2.4km (1.5 miles) from the start to allow the field to spread out while competitors must at all times ski within the wake of their own boat. Each boat is required to carry a variety of safety equipment; this includes a suitable anchor and line, fire extinguishers, compass, flares, paddles, ignition cut-out fastened to the driver, and buoyancy aids. Two crew members are required; both must wear a life-jacket with inherent buoyancy and a fluorescent orange crash-helmet. The skier wears a lightweight plastic helmet which must cover the ears for protection in the event of a fall sideways. The slits in the helmet must be large enough to allow good hearing, but not so large that water rushes in with such force that the ear drum is perforated. The average rope length is about 45m though longer ropes are used in Australia and USA in races in calm lakes and rivers.
The tactic used by Italian skiers of wrapping the rope handles round the body to take the strain off the upper limbs has been banned from international use on safety grounds. A technique introduced by Australian competitors to allow greater endurance gained international acceptance in 1979: both handles are placed behind the lower back at about hip height and held by one hand while the other holds an additional forward handle .
In water ski jumping, competitors take off from a ramp 150cm high for boys and females and 180cm for men. Pre-ramp velocities approach lOOkmh-1 which may increase further with reduced friction between skis and wood or plastic ramps while distances exceeding 40m are jumped in major events. Extensive abrasions are likely if the skier misses the end of the ramp but hits the side, or prematurely falls and is carried up the ramp by the momentum developed. The sides of ramps should be covered with protective shields which deflect bodies on impact courses. As he rises up the ramp he must counteract a downward force estimated at three times his body weight to prevent bunching at the hips and knees and develop thrust for the jump (Bass, 1971). If balance is lost in the air the greatest dangers are in being hit by a flying ski and in landing awkwardly.
Greater impact forces on landing (6.5G for 95 milli-seconds(ms)) than at take-off (5.0G for 95ms) were reported by Reid and colleagues (1978) for men at the Canadian championships. They concluded these forces were insufficient to result in direct injury to healthy athletes but that frequent exposure to these impacts could prove hazardous to the water ski jumper. They cited findings of considerably higher incidences of flexion/compression injury to the lumbar dorsal spine, including anterior wedging of the vertebral bodies, narrow disc spaces and osteochondroses of the vertebrae than in the general population.
After landing from a bad jump the skis may begin to sink at the rear as the rope slackens. When it becomes taut the skier may suddenly be pulled violently forward off his bindings on to his own skis and suffer head or facial lacerations (Bass, 1971). Protective helmets would prevent such injuries. Another cause of injury could be skis crossing on landing after balance is lost in mid-air.
Overall championships incorporate slalom, jumping and trick-skiing into a combined event. Tricks may involve turning 180° or 360° at a time, turning while crossing the wake or with the tow rope hooked around the foot. Competition involves two 20 second(s) runs before a panel of five judges. Champion amateurs may eventually become professionals and display other tricks working with a partner or in echelon and coordinating manoeuvres. Injuries may be caused by the ski, the rope or from loss of balance. Skis used are lm long, 15cm wide with rounded ends slightly turned up and no fins. Since trick-skiing requires difficult operations and exceptionally high skill, it is imperative that routines should only be attempted after considerable instruction. Adverse sequelae are mostly brought about from taking undue risks. Though severe injuries do occur in water skiing their incidence is low when the large numbers participating are considered.
Falling awkwardly is an obvious cause of sprains, joint dislocations and ligament tears in all forms of water skiing. Falling forward in a spreadeagled posture with arms outstretched leaves the shoulder joint especially vulnerable. The best procedure for the beginner to adopt is either to attempt to sit or roll over. In learners, the skis begin to part sideways before loss of control and the abduction force applied may damage medial knee ligaments or medial and lateral ligaments of the ankle. Landing in a splits position may produce ruptures in abductor muscles and capsular sprains of the hip and is common to jumping, slalom and recreational skiing.
The nylon tow rope, usually about 23m long, may cause lacerations or friction burns at take-off or in falling by pulling across exposed skin at any body pan. For safety, the slack is taken up at the start of a run prior to rapid acceleration and care taken that the rope is unwound and floating freely in front of the skier. The whiplash effect of a broken rope may cause similar effects and possibly sever a finger tip (Bass, 1971). Tendon injuries to fingers may also occur if caught in the tow ropes or handles.
The driver should be skilled and accompanied so that both the path ahead and the skier behind can be under surveillance. A wide rear view mirror can assist as does a communication code between skier and boat operators using recommended hand signals. O’Brien et al (1978) reported paralysis in the deltoid and extensor muscles of right arm and wrist after their patient was thrown in the air with the arm forced backwards when another boat cut across his tow rope. Collisions between boats are less frequent than accidents from hitting fallen skiers or swimmers. Collisions with solid objects such as floating debris, submerged rocks, or hitting a dock or pylon of a jetty due to misjudgment of distance may produce a variety of injuries.
Boat propellers can be lethal, causing amputations or fractures of extremities. This could happen if both driver and accompanying observer are looking behind and is completely avoidable. Sleight (1974) reported severe multiple injuries in a skier run over by the driver dazzled by the sun’s reflection as he returned to pick him up after a fall. Skiers are more conspicuous in the water if they hold up a ski while drivers should steer away from areas occupied by casual surfers and swimmers. Water skiers are separated from other water users in controlled club practices. Most countries legislate to prohibit skiing in a channel close to shore and watersport centres have recognised capacities.
Falling may induce forceful entry of water into body cavities. Sinusitis and otitis media can arise from water entering the nose or ears. A perforated ear drum can present complications as the tympanic membrane may not completely repair. Bathing caps afford ear protection while ear plugs may only be forced deeper into the aural canal. The rectum may suffer if the individual falls in a sitting position and rectal douches occur if rising from a crouched starting posture is delayed. Ramey (1974) reported intra-rectal tears in a female skier after falling and dislodging her bikini to one side. Vaginal douches can produce salpingitis with risks of later sterility. Neoprene rubber pants provide adequate protection for experienced and novice skiers and may be lined with reinforced nylon.
Moore (1964) reported two fatalities from fracture-dislocation of the cervical spine on falling when coming into land at high speed. Paterson (1971) found dislocations of the fifth and sixth cervical vertebrae with locked facets and temporary quadriplegia when a skier hit a submerged sandbank and a crush fracture of the body of the fifth cervical vertebra in another individual falling on coming in to land and hitting his head on a bank concealed below the water’s edge. Soft internal organs can be damaged from the quick deceleration in crashing on to the shore or jetty. These accidents can be prevented by approaching gently and parallel to the beach until running out of speed.
ROWING AND CANOEING
Rowing constitutes strenuous physical exertion placing high demands on aerobic and anaerobic mechanisms (Di Prampero et al, 1971; Hagerman et al, 1975). The total energy requirement for rowing an international 2 000m course has been estimated to be approximately 250kcal or 1 046kJ with an 18 per cent contribution from anaerobic processes at top speeds (Jackson and Secher, 1976). These authors found single sculls to be more costly in energy production than doubles or cox-less pairs at a similar velocity. Performance is faster in doubles where each partner uses two sculls than in coxless pairs where each individual uses one oar. Olympic oarsmen tend generally to have high absolute maximal oxygen uptake values (Nowacki et al, 1969; Di Prampero et al, 1970). Great force is also required (Secher, 1975), the strain on the oar reaching 80 to 100kg in the study of Tokyo Olympic rowers (Ishiko, 1971). The primary source of power is the thrust of the legs supplemented by the vigorous action of the back and transmitted through the shoulders and arms to the oar. Rowing skill is demonstrated in economy of effort and in coordinated team-work. The sport provokes relatively few serious injuries and these are mainly due to faulty technique. Muscle tears and back injuries to ligaments or muscles may occur in land training or in lifting the shell from the water. The characteristic injuries associated with water work are back injuries, tenosynovitis and blisters.
Both the legs and the back are used vigorously with each stroke . Muscle injury particularly in the lower back can be due to repetitive training, since fatigue can only be alleviated by introducing breaks and hence disrupting the rhythmic movement. Too much forward swing can lead to strain in the back or shoulder muscles before the powerful leg action commences the sequence. Abdominal muscles may be injured when underdeveloped in the early stages of training or if the rower lies too far back at the finish of the stroke. Besides transmitting the force developed to the oars the arm muscles place and retrieve the oars in the water. All rowing techniques require good coordination of the muscles involved with the blade taking firm hold of the water and releasing cleanly. Movement of the oars of a crew above the water is found to be nearly uniform in top rowers but this does not ensure uniformity of movement of oars in the water which is more difficult to perfect (Ishiko, 1971).
Tenosynovitis or tendinitis in the sculler or oarsman usually involves inflammation of the extensor tendons of the forearm. Pain is felt while the hand is dorsiflexed during feathering the oar as the blade is taken parallel to the water surface to reduce air resistance (Schwartz, 1971). The hand farthest up the oar achieves this by rotating the oar handle. A practical measure to avoid aggravating the inflammation is for the oarsman to change sides, a solution not applicable to scullers. Tenosynovitis may also be attributable to gripping the oar too tightly on the inside hand. In this case a more relaxed hold is advised. Treatment of the condition on recurrence is far less straightforward and specialist sports medical attention should be sought.
A pervasive affliction of rowers is blisters, particularly of the hands and buttocks. Novices, especially females, are susceptible. Vulnerability is greatest at the beginning of a period of training before the hands harden. A simple bandage may be adequate in treating finger blisters while a tight-fitting leather glove can be worn for protection while the palms heal. If blisters continually recur on the palms the technique is probably faulty. Blistered buttocks can be afforded some protection by wearing tight-fitting underpants which help to reduce friction on the skin. This area may also be blistered if training is prolonged in wet conditions while heels may suffer from contact with wet socks. Blisters should always be carefully treated, especially if the skin is broken. Sound hygiene, and daily laundering of kit is recommended in order to avoid infection. A less frequent complaint is abrasions on the back of the calf. These may be prevented by adjusting the seat height.
Canoeing and kayak paddling involve various forms of speed and wild-water events in specially designed crafts. The kayak has a pointed bow and stern, and low sides and is covered except for the cockpit. In sprint competitions the paddle has double blades for alternate use on each side of the kayak while the operator adopts a long-seated position. Flat water competitions range from 500 to 10000m for men and 500m is the standard international distance for females. In wild-water disciplines slalom competitions are held on rapid rivers over a course designated by a number of gates each consisting of two poles suspended vertically between 1.3 and 3m apart. Competition, normally lasting 3.5 to 4.5 minutes, involves the negotiation of gates in a predetermined order, and forward and reverse paddling in upstream and downstream manoeuvres. In wild-water down-river racing the competitor encounters a succession of rapids through which he chooses his own route while competition duration may vary between 13 to 35 minutes. The Canadian (cl) canoe is paddled on one side from a kneeling position. The wild-water events emphasise muscular endurance as well as strength in the trunk, shoulders and arms and skill in handling the craft.
The greatest hazards in canoeing and kayak paddling are drowning and exposure to cold. A life-jacket made of closed-cell vinyl or unicellular plastic foam is an important item of equipment for the canoeist. The ability to aright a capsized craft quickly is important and is usually developed in the early stages of learning. Even top canoeists capable of efficient first time canoe rolls, view immersion in hazardous winter spate with concern. Attendant symptoms can include severe fore- head pain, breathing and speaking difficulties as well as visual disturbance, dizziness and disorientation (Baker and Atha, 1977). Clothing with appreciable insulation is recommended when training in cold conditions. Close-fitting wet suits of foam neoprene, vinyl thermal socks, cotton sweat pants and fish-net underwear afford protection against exposure. A wet suit also helps to prevent the lacerations which are possible when capsizing in rapids. In these circumstances, protective headgear is essential. Skill in esquimautage is especially important to allow recovery in traversing in rocky rapids.
The functional curvature of the spine in the direction opposite the paddling side is likely to become permanent where paddling is exclusively on one side of the craft . The dorsal musculature develops assymetrically as it hypertrophies and shortens on the paddling side while becoming lax and more spare on the opposite side. The spinal column may become slightly scoliotic as a result but corrective exercises can facilitate even bilateral development.
The immediate interface between the individual and equipment used accounts for many of the ailments suffered. Gripping the paddle too tightly can cause blisters on the hand. An incorrect grip may eventually provoke tendovaginitis in the forearm. Boils on the buttocks may follow abrasions and infection after lengthy periods using a wet seat or poorly fitting pants. Lesions and abrasions can also occur on the outside of the legs from contact with the inner side of the craft. Bursitis of the knee may afflict individuals operating from a kneeling position as in cl rowing.
Pelle (1971) listed myalgia in the forearm muscles and acute or chronic pains in the shoulder joint as typical aggravations. The joint is likely to be unduly strained on the paddling side if improper technique is used. Extended practice of eskimo rolls is a possible cause of sinus infection (Brown, 1971).
Risk of injury in surfboarding has been estimated at 1 per 17 500 surfing days – an incidence well below most sports (Allen et al, 1977). The most frequent cause of injury is being hit by a loose board. Injury from one’s own board characteristically occurs when surfacing after being thrown into the water. Trauma can include a maxillo-facial fracture, abdominal and eye injuries and varying degrees of renal contusion if struck in the flank. Allen and associates reported a fatality due to severing of the carotid artery by a skeg from a loose board.
Surfboard leashes or ‘ding-strings’ minimise the chances of injuring others but increase the likelihood of self-injury. Serious injuries including toe amputation, lacerations and blunt trauma have been reported (McDanal et al, 1976). Near-drowning is another potential hazard (McDanal et al, 1977).
The original Malibu boards, about 3m long and 14 to 16kg weight, were paddled out from a kneeling posture. After one season surfing nodules have been found in the pressure points on the tibial tuberosity. These lesions are generally bilateral and appear to be a bursal cyst of the subcutaneous infrapatellar bursa (Cragg, 1973). A rubber suit extending over the knee prevents trauma. The shorter fibre-glass boards (2m long or less and weighing between 9kg and 5kg) can be paddled prone and avoid this injury. The standard 23cm keel or skeg on most current boards gives better stability but make a loose board more dangerous. The smaller boards produce more stress on the elbow, being more difficult to paddle. Epicondylitis can result and can also occur due to frequent mounting of the board or holding on to it as waves break (McDanal and Anderson, 1977).
The turbulence of large ocean waves forces water into the ear canals of the surfer. Exposure to cold ocean water for many years can be an important aetiological factor in hyperostosis. This usually manifests with a diffuse rounded bony protuberance of the anterior and posterior osseous canal wall (Seftal, 1977). The stimulation of new bony growth is usually bilateral in surfers. Septal estimated that surfing for two hours each day for four to five days a week in water between 10 to 15.5 °C would take 7 to 10 years to develop moderately severe ear canal hyperostosis.
It is easy to appreciate the attraction of outdoor water based activities especially to urbanised communities and during sun-drenched summers. The seas, lakes and rivers have a characteristic lure that may obscure the dangers inherent in engagement in aquatic recreations. In general, risk factors may be associated with the individual, the craft used, the weather and water conditions or with the particular activity. Responsibility is placed on the shoulders of the participant for thorough prior organisation and sensible judgement. It is important that the safety procedures outlined by the relevant sports association be carefully adhered to. Life-belts and fail-safe systems should be used where advised as well as appropriate protective clothing. Proficiency in swimming should be developed and at least an elementary knowledge of life-saving is important. Attention is also directed to craft maintenance and courtesy to other water users. Correct technique in the specific skills of the sport should be acquired in the early stages of participation. In the more rigorous water sports, land drills should be executed efficiently to avoid injury promotion and the need for physical conditioning appreciated. With a sound preparation for outdoor water sports, confidence and enjoyment can only be enhanced by a safety conscious approach to participation.
Allen, R. H., Eiseman, B., Strachley, C. J. and Orloff, B. G. (1977). Surfing injuries at Waikiki. Journal of the American Medical Association, 237, 668-670.
Baker, S. and Atha, J. (1977). A survey of disorientation and other problems among canoeists following immersion in cold water. British Journal of Sports Medicine, 11, 179.
Bass, A. L. (1971). Acute and subacute injury: water skiing. In L. A. Larson (ed). Encyclopedia of sports sciences and medicine. Macmillan, New York.
Brown, J. M. (1971). Acute and subacute injury: kayak. In L. A. Larson (ed). Encyclopedia of sports sciences and medicine. Macmillan, New York.
Cragg, J. (1973). Surfers’ nodules. British Journal of Clinical Practice, 27, 418-419.
Crampton, B. A. and Tubbs, N. (1977). A survey of sports injuries in Birmingham. British Journal of Sports Medicine, 11, 12-15.
Di Prampero, P. E., Pinera Limas, F. and Sassi, G. (1970). Maximal muscular power, aerobic and anaerobic, in 116 athletes performing in the XlXth Olympic Games in Mexico. Ergonomics, 13, 665-674.
Di Prampero, P. E., Cortili, G., Celentano, F. and Ceretelli, P. (1971). Physiological aspects of rowing. Journal of Applied Physiology, 31, 853-857.
Hagerman, F. C, McKirnon, M. D. and Pompei, J. A. (1975). Maximal oxygen consumption of con-ditioned and unconditioned oarsmen. Journal of Sports Medicine and Physical Fitness, 15, 43-48.
Ishiko, T. (1971). Biomechanics of sport. In Medicine and sport, Vol. 6: Biomechanics 11. Karger, Basel.
Izeki, J. (1973). Statistical observation on sudden deaths in sport. British Journal of Sports Medicine, 7, 172-176.
Jackson, R. C. and Secher, N. H. (1976). The aerobic demands of rowing in two Olympic rowers. Medicine and Science in Sports, 8, 168-170.
McDanal, C. E., Anderson, B. S. and Sims, J. K. (1976). Ding-string injuries. New England Journal of Medicine, 295, 287.
McDanal, C. E. and Anderson, B. (1977). Surfer’s elbow. Hawaii Medical Journal, 36, 108-109.
McDanal, C. E., Rosario, M. D., McDanal, J. O., McNamara, J. J., Anderson, B. S., Springer, W. N. and Sims, J. K. (1977). Near drowning from ding-string surfboarding; a case report. Journal of the American Medical Association, 238, 398.
Moncur, J. (1973). A study of fatalities during sport in Scotland (1969). British Journal of Sports Medicine, 7, 162-163.
Moore, A. T. (1964). Water skiing. In J. R. Armstrong and W. E. Tucker (eds). Injury in sport. Staples Press, London.
Nowacki, P., Krause, R. and Adam, K. (1969). Maximal oxygen uptake by the rowing crew winning the Olympic Gold Medal 1968. Pflugers Archiv, 312, 66-67.
O’Brien, M., Bonner, F. J. and Bonner, J. F. (1978). Electromyographic evaluation of a water skiing injury. British Journal of Sports Medicine, 12, 142-144.
Paterson, D. P. (1971). Water skiing injuries. Practitioner, 206, 655-661.
Pelle, L. (1971). Acute and subacute injury: canoeing. In L. A. Larson (ed). Encyclopedia of sports sciences and medicine. Macmillan, New York.
Ramey, J. R. (1974). Intrarectal tear with bleeding from water skiing accident. Journal of Florida Medical Association, 61, 162.
Reid, J. G., Kopp, P. M. and Verhoeven, A. P. (1978). Impact forces on water ski jumpers. In E. Asmussen and K. j0rgensen (eds). Biomechanics Vl-B. University Park Press, Baltimore.
Schwartz, R. A. (1971). Acute and subacute injury: rowing. In L. A. Larson (ed). Encyclopedia of sports sciences and medicine. Macmillan, New York.
Secher, N. H. (1975). Isometric rowing strength of experienced and inexperienced oarsmen. Medicine and Science in Sports, 7, 280-283.
Seftal, D. M. (1977). Ear canal hyperostosis – surfer’s ear. Archives of Otolaryngology, 103, 58-61.
Sleight, M. W. (1974). Speedboat propeller injuries. British Medical Journal, 2, 427-429.