It is well documented that women suffer 4-6 times the number of knee injuries during sport than do men. A few years ago, our team at the Cincinatti Sportsmedicine Research and Education Foundation attempted to determine whether this statistic could be reversed by specific training of women prior to undertaking sports activities [see original publication].
The National Collegiate Athletes Association (NCAA) estimated an incidence of 1 in 10 knee injuries amongst the 100,000 American collegiate women participating in sports each year.
They drew attention to the massive cost - pointing out that cruciate ligaments alone in this group cost US$37 million a year! They estimate the total annual cost of serious knee injuries in USA women athletes (high school plus college) to be in the order of US$100 million a year.
In our study we set out to determine whether specific pre-sports training might reduce this crippling expense.
Explanations in the medical literature for the comparatively high incidence of knee injuries in women included:
In a previous study in which I had been involved our group had found that four out of five ACL injuries in athletes occurred from a non-contact mechanism, the majority occuring while landing from a jump. We decided in this new study to take our investigations further, and give a group of 366 women a comprehensive program of training and coaching throughout a season, including particular emphasis on landing from jumping.
This study group we would then compare with two 'control' groups -
We had taken all three groups from well known jumping sports - volleyball, soccer or basketball. All were high school aged athletes.
Coaches of the test group of women were given an instructional video and training manual to cover a six week program incorporating flexibility, plyometrics and weight training. Details of the regime are in the appendix of our original publication. An athletic trainer and physiotherapist were also assigned to the groups to demontrate plyometrics and stretches, and to improve form. The other two groups did not participate in the training programme.
Over the period of study we managed to monitor 94% of the athletes through the entire season and all knee injuries were carefully documented. Any suspected ACL ruptures were confirmed by arthroscopy. Standard statistical methods were used to analyse our results. There were some design faults in our study, but we nonetheless feel that the results are significant.
There were no serious knee injuries in the volleyball players in any of the groups. Taking the results for soccer and basketball, though, we found the untrained female athletes had 5.8 times the number of knee injuries than the men. Lack of training particularly predisposed the women to ACL injury.
Training significantly reduced the number of injuries in women, but even then this group had 2.4 times the number of injuries as the men, suggesting that factors other than training are also very relevant.
Hamstrings muscles resist the forces that strain the ACL, while the quadriceps muscle has the opposite effect. In untrained female athletes the quads are generally relatively stronger than the hamstrings, and the ACL is put at risk. Hamstrings-to-quads ratio should be about 65% in the trained knee. Ratios below 60% predispose the ACL to injury. Ratios below 50% should be considered abnormal.
We believe that the major benefit of a jump training program which includes progressive resistance weight training for the lower extremity, other than a general improvement in technique and strength, is gained from improvement of the hamstrings-to-quadriceps ratio.
Improvement is also gained from decreasing what is called 'abduction and adduction moment', ie stabilizing the knee from stressing into a bow- or knock-knee position on landing.
We recommend that serious attention be given to instituting similar training programmes in women's teams where jumping and landing put the ACL at risk, in order to reduce cost both in terms of medical care and personal suffering. Specifically hamstrings-to-quads ratio should be optimised to protect the ACL.