Understanding the biomechanical principles in the study of sports has become important in developing techniques on how a player’s movements should be properly executed, for the improvement of accuracy and efficiency of the player’s movements, and for preventing injuries attained during sports.
Volleyball is a popular competitive sport. Being one of the games played in different schools and universities and in past Olympics demonstrate that the level of play and interest nationwide is increasing. It ranked 26th in the table of most-played sports and physical activities by adults in Australia (22nd in the table for Victoria) (Cassell 2005). ernational Volleyball Federation (Federation Internatonale de Volley-Ball – FIVB) claims 800 million participants world-wide who play at least once a week which could possibly makes itl ranks as the world’s most popular participation sport (Briner ; Kacmar 1997 as cited by Cassell 2005).
Volleyball combines skills including agility, strength, vertical jump and hand eye coordination. Often times an imbalance in one or more of these components can lead to injury (Mumford 2005). With all of its jumping and diving activities, volleyball remains a game with a high injury rate. An increase in sports related injuries, particularly to the lower limbs has increased over the past decades. Compared with other ligaments supporting the knee, rupture of the anterior cruciate ligament has been the commonest and has the greatest potential to cause both short term and long term disability (Cross 1998).
The knee joint is designed like a hinge that has a limited movement. It moves back-and-forth but not side to side. This motion is controlled and limited by ligaments that support the knee joint. The ACL is a tough fibrous structure that attaches the tibia (lower leg bone) to the femur (thigh bone). It is the most important stabilizer of the knee. This ligament helps to stabilize the knee by preventing excessive forward movement of the tibia on the femur (York, 2005). It has a tensile strenght of 2160 ± 157 N and stiffness of 242 ± 28 N/mm. Passive knee extension produces forces along ACL only during last 10 degrees of knee extension (Woo et al 1991).
The anterior cruciate ligament (ACL) has been regarded as an isometric ligament although some authors disagree with this. It accepts 75% of anterior force (Wood et al 1991). Li et al demonstrated that the ACL decreased its length as the knee moved from full extension to 90 degrees of flexion. Its length at 30 degrees was slightly less than at full extension. The decrease in length from 60 degrees to 90 degrees of flexion was about 10%. , anterior cruciate ligament forces range between 50 and 240 newtons at 5 degrees of hyperextension (Woo et al 1991). These data suggest that the ACL has its main role in preventing anterior tibial translation at low flexion angles, and this function diminishes with increased flexion. Also, the ACL starts with an internally rotated position of approximately 10 degrees at full extension, which increases to 20 degrees at 30 degrees of flexion. As the knee flexes, the orientation of the tibial insertion changes with respect to the femoral insertion area. This is due to the “screw home” mechanism of the knee (Ruiz and Barber, 2005).
The most common cause of anterior cruciate ligament (ACL) rupture is a traumatic force being applied to the knee in a twisting moment (Figure 1) (Roye, 2004). It may occur from a sudden stop, twist or hyperextension and not from a collision (York, 2005). ACL injuries may occur from coming to a quick stop with a directional change while running, pivoting, landing, or overextending the joint in either direction (Roye, 2004).
Figure 1
There are a variety of factors from which ACL injuries are attributed. These could be biomechanical or non-biomechanical factors. Non-biomechanical factors include anatomical, hormonal and environmental and are non-modifiable. Biomechanical aspect on the other hand is more important that it directly influence the stress placed on the ACL during a game and should be understood by players and instructors so as to prevent serious injuries in volleyball and other sports. These factors include joint motion, joint forces, muscle activation, and muscle strength. Both the non-biomechanical and biomechanical factors influence the greater risk of ACL injury in females as demonstrated in the conference held Hunt Valley, Maryland in June, 1999 (Padra 2004).
The rates of discrepancy between incidence of ACL injury for men and women are believed to be based on anatomical and physiological elements that influence knee injury. Extrinsic factors include muscular strength, level of conditioning, shoes and motivation. Intrinsic factors on the other hand includes joint laxity, limb alignment, intercondylar notch size and shape, ligament size, and hormonal influences (Harmon 2000 as cited by Tillman, Hass and Brunt 2002).
As cited by Cariati (2001), there studies performed by the Michigan team that point out the possible reasons differentiating the incidence of anterior cruciate ligament injury between male and female volleyball players. Unlike male players, women tend to land with a straighter knee after jumping. This position of landing places much more forces which subsequently straining the anterior cruciate ligament of women. Female hormone which is estrogen plays also a major role in the incidence of the injury. Training programs can also be considered because women’s muscle may not be prepared to handle the strain of high, forceful jump and the impact of improper landing on the anterior cruciate ligament making it more frequently acquired by the women than the males who participate in the same sports.
During volleyball, it is more likely that shoulders are injured after spiking and blocking without giving attention to possible ACL injury after landing from a high jump or explosive stride. According to Watkins (1992), 70% of volleyball injuries are associated to blocking and spiking. The improper jump-landing sequence has the highest risk of acquiring ACL injury among volleyball players (Figure 2) (Dubin, 2002). Based on the analysis of Stacoff and colleagues (1988) (as cited by Tillman, Hass and Brunt, 2002), there is 1000 N to 2000 N initial vertical impact peak at forefoot touchdown during volleyball block jump in adult male athletes. Heel strike followed with an impact peak ranging from 1000 N to 6500 N. ACL prevents the knee from hyperextension. Knee overextension may produce a great impact on landing and subsequently causes injury on this structure. It was found out that as the height of the jump as well as with knee extension angle increases, vertical impact forces also increases (Dufek and McNitt-Gray 1990 as cited by Tillman, Hass and Brunt, 2002).
Figure 2
The height of the jump and the subsequent touchdown velocity were less important, however, than knee angle in predicting the magnitude of the ground reaction force (GRF). Increased knee extension produced a greater impact on landing. Other researchers have found that vertical impact forces increase with the height of the jump as well as with knee extension angle (Dufek and McNitt-Gray 1990). McNitt-Gray found that greater landing velocities produced greater knee extensor moments, suggesting that the quadriceps acted as shock absorbers (Tillman, Hass and Brunt, 2002).
A plyometric (jump training), stretching and strength training program should be considered for all players to decrease peak landing forces, and particularly for female players to correct imbalances between hamstring and quadriceps muscle strength (Cassell, 2005). Plyometric training should be under the supervision of a trained coach and programs should be carefully evaluated. Players who are already proficient jumpers, middle blockers and players with knee pain are advised to decrease their jump training time and pay close attention to technique (Cassell, 2005).
Volleyball is a game of power that involves a combination of strength and speed. As a result, you need to train with weights to develop strength in your upper body, back and shoulders as well as your legs. Finally, to avoid injury while improving your vertical jump, try to practice jumping as you would during a game. This means practicing your footwork in blocking and spiking and then jumping as high as you can (Bragman, 2004). More importantly, practice proper and balanced landing with proper knee bending.
Athletes, especially volleyball players are advised to be knowledgeable enough when they encounter injuries such as anterior cruciate ligament injury. They should take a rest, therefore, refraining from active sports for it may aggravate the injury. They should place ice over the the affected area and compress it with cloth or bandage to minimize the pain and inflammation. It should be elevated until pain and swelling subside. If the pain and swelling persist, athletes are advised to consult their doctor for possible interventons.
Trainors, coaches even if the athletes should work hand in hand to find ways and means to formulate training programs for anterior cruciate ligament prevention for it may reduce the risk of anterior cruciate ligament injury and reduce the possible financial costs and long-term disability associated with ACL injury (Padra 2004).
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