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Information about project titled 'The effect of a center line rule change on the incidence of ankle sprains and rule violations in women's collegiate volleyball'

The effect of a center line rule change on the incidence of ankle sprains and rule violations in women's collegiate volleyball

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Project status: Published
Project manager: Jonathan Reeser
Coworker(s): Julie Agel, Randy Dick, Roald Bahr


Ankle ligament sprains account for as much as half of all acute volleyball injuries, and in earlier studies we were able to document that the most common cause of injury was when a blocker lands on the opposing attacker's foot (50% of all sprains). In half the cases there was a rule violation with the attacker crossing the center line under the net.

We therefore thought that to increase the distance between the players by not allowing anyone to step on the center line would move the attacker and blocker farther away from each other and thus reduce the risk of injury.
However, when we set out to test this hypothesis in a pre-season tournament in Norway, the more restrictive rule increased the number of rule violations such that about 8% of all rallies were terminated because of players stepping on the line (vs. the normal 0.3%). Almost all of the rule violations occurred in situations with very low injury risk. We therefore concluded that the number of rule violations resulting from the rule change was unacceptable, and the study was terminated before we were able to show whether the rule change would lead to less injuries. At the FIVB World Congress in Tokyo in 1998 there was a proposal for a more radical rule change, i.e. to allow the players to step completely over the line as long as there was no interference with the opposing team.
However, this rule change was stopped for fear of more injuries. An alternative rule was designed to eliminate the dangerous situations and still keep the number rallies that were stopped because of center line rule violations to a minimum. The NAGWS, which apply to women's collegiate volleyball in the United States, adopted in 1998 a more liberal center line rule which, it seems, may fulfill these objectives. The NAGWS rule allows complete encroachment into the opponent's court by hands/feet as long as (1) there is no safety hazard; (2) there is no contact with the opponent; and (3) the distance of the encroachment is not significant. A safety hazard was said to exist anytime an opponent or teammate is jumping nearby (i.e., that center line violation will be called). Based on data from the NCAA Injury Surveillance System (ISS) for the 1997-98 seasons (before the rule change) and the 1999-2000 seasons (after the rule change), we set out to assess whether the rule change had any effect on the incidence of ankle sprains.

Ankle injuries have been the leading volleyball related injury reported by the ISS in each season since 1984. The average incidence of ankle sprains during the four year study period from 1996 to 1999 was 1.48 ± 0.24 per 1000 athlete exposures (AE; training sessions or games). However, there was no significant change in the rate of game-related ankle injuries occurring during the two seasons before (1996 & 1997: 1.54 ± 0.25 sprains per 100 AE) and after the rule change (1998 & 1999: 1.42 ± 0.20 sprains per 1000 AE; p=0.55). Ideally, rules governing athletic contests should function to create a safe environment in which the participants can compete fairly. Unfortunately, it is impossible to legislate injuries out of existence.
However, rules that clearly increase an athletes risk of injury in a sport should be changed if reasonable alternatives exist which do not otherwise detract from the athletes or spectators enjoyment of the contest. The original proposal to penalize any contact with the centerline clearly was not feasible for this reason.
However, our observations suggest that a rule which makes any contact with the centerline in the area in which the ball is being played a fault - but is more permissive in other situations - may not only be acceptable in terms of the "flow of the game" but, more importantly, could potentially result in a significant reduction in the incidence of volleyball-related ankle injuries. The rule we are proposing would eliminate the legal "conflict zone". Front-row attackers would therefore be compelled to be more cognizant of the centerline or else risk a centerline violation and loss of a point. This should reduce the incidence of contact between opposing players under the net and thus reduce the incidence of ankle injuries. Under the newly modified rule, it would remain within the referee's judgment to determine if centerline violations away from the ball should be penalized. This would help to counterbalance any (temporary) increase in the total number of centerline violations following introduction of the new rule, thereby serving to maintain the pace and flow of the game.

We propose that this new rule be adopted for a minimum two-year trial period, during which time injury surveillance would continue under the auspice of the NCAA ISS to assess the effectiveness of the rule change.