The only previous prospective study (Wang and Cochrane) was based on 16 athletes. In the current study, 66 volunteer players (average age 24) were recruited among 9 Division I and Division II volleyball teams. These volunteers included 34 men and 32 women, and a total of 57 right-handed players. They had all been playing volleyball for a dozen years on average.

Before the 2008-2009 season started, when they were training 13 hours per week on average, they completed a questionnaire on amount of practice time, their playing career, the position they played, etc. They also reported on previous shoulder pain or injury, including their diagnosis and treatment programme. It turned out that 52% of the study’s players mentioned having had previous should pain or injury in their dominant shoulder. 

Additionally, the players all underwent an extensive physical examination of both shoulders before the start of the season. "We evaluated muscle strength - the isokinetic assessment - using a dynamometer, a tool for measuring maximal strength which is considered to be the gold standard in the field," says Bénédicte Forthomme. It enabled the researchers to measure the maximum force exerted by rotator muscles during movement, both in the concentric mode (while hitting the ball) and in the eccentric mode ("deceleration"). These measurements were critical in order to determine whether there was a muscular imbalance.

An assessment of stiffness and scapular malposition (using morphostatic measurements) was conducted through a series of precise, standardised, and thorough clinical measurements in order to ensure that the study produced usable data. "We made sure that the measurements were valid and reproducible for the same person. Otherwise it would have been impossible to have our results published in a leading sports medicine and traumatology journal, as is the case,” explains the scientist.

Next: monitoring 

During the 6-month competition period (October to March), the players completed a weekly questionnaire with the help of a physiotherapist or member of the athletic staff, in order to identify and describe any shoulder problems they may have experienced and the resulting sporting time lost. The severity of the injury was classified according to absence from the sport (less than a week, between one and three weeks, or longer than three weeks). 

This precise monitoring revealed that 23% of the players suffered from dominant shoulder pain during the season (not as a result of traumatic causes). Out of these 15 players, 13 were spikers. Analysis of the results showed that men were 6 times more protected than women from the risk of injury. This corroborated the hypothesis that "muscular strength" plays a protective role.

Furthermore, and this is an essential point, the study revealed that those with a previous injury were 9 times more likely to sustain another injury. In other words, it would seem that it is either difficult to completely recover from an initial shoulder injury, or the risk factors that led to the first injury were not addressed!

The study's conclusions don't stop there. Indeed, Bénédicte Forthomme was also able to answer questions she had from the very beginning, namely: What are the main causes of injury? What are the risk factors? What are the protective factors?

Among the risk factors for tendinopathy, one factor seems more important than all the others. It doesn’t originate in the scapula, nor is it related to stiffness problems. Rather, the study showed that this injury was related to eccentric strength of the rotator cuffs, which allows the player to decelerate. In fact, in order for the shoulder to be "protected", the muscles must hold the arm back during extreme and powerful movements: non-injured players exhibited the best deceleration strength during cocking and throwing movements (internal and external rotators in the eccentric mode), while measurements of injured players revealed an initial reduction in deceleration strength.