Does your daughter, sister or best friend play soccer or basketball? Are you a personal trainer? Are you coaching women’s league play? Then this information is for you. Have you suffered an ACL injury putting you on the sidelines for 9-12 months? Then read on!
Not too many years ago a female cousin of mine received a full scholarship to play basketball for The University of Oklahoma. Of course we were all elated. She had been a top Texas High School player and AAU (American Athletic Union) champion. She did great her freshman year and in fact was a starter and played every game due in part to two upper classmen experiencing ACL (anterior cruciate ligament) tears early in the season. The Anterior Cruciate Ligament is an important knee ligament that prevents forward movement of the lower leg bone (tibia) relative to the upper leg bone (femur). Unfortunately, my cousin also had an ACL injury her sophomore year. She, however, returned for her junior and senior seasons with no further injuries. ACL injuries occur all too often in female athletes.
The greater incidence of ACL tears in females versus males playing non contact sports such as soccer or basketball has been well documented. The literature (3) suggests that an imbalance between the quadriceps and hamstring muscles, the primary stabilizers of the knee, continues to be a contributing factor in ACL injuries . The hamstring: quadricep (H:Q) ratio is determined by dividing the hamstring by the quadricep strength as measured on an isokinetic testing device. An improper strength ratio may predispose an individual to ACL injury. Females tend to be quadriceps dominant meaning that their hamstrings are weak relative to their quadriceps. Males tend to be hamstring dominant meaning their H:Q ratio is higher than what is typically seen in females.
One study by Hewett et al. (2) looked at using plyometric exercises to improve the H:Q ratio in female athletes. They observed decreased impact forces at the knee and increased hamstring strength after participating in plyometric training. In addition they observed reduced incidence of knee injury when compared to those who did not participate in the plyometrics program. Studies (1,5) suggest that plyometric training is a safe way to increase muscular strength, power and joint stability while improving functional movement patterns.
Kavin, et al. (4) evaluated the effects of plyometric training on the H:Q ratio in recreationally active women. Twenty five women with an average age of 20 years old participated in the study. The training program consisted of 13 lower extremity plyometric exercises, varying in difficulty and intensity. During each training session (done in a group setting and led by a qualified instructor), subjects completed at least 7 exercises selected from a total of 13 exercises. Time spent in training sessions was 45-60 minutes 3 times per week for 6 weeks.
Below is a complete list of the plyometric exercises used in the Kavin et al. (4) study with a few descriptions of some selected exercises.
Tuck jumps begin from a standing position, jump and bring both knees up to the chest as high as possible.
Scissors jumps begin in stride position, jump and alternate position in mid air.
Bounding for distance begin by bounding in place, slowly increasing in distance with each step keeping knees high.
180 degree jumps is a two-footed jump, rotate 180° midair, hold landing for 2 seconds, and reverse direction.
Study Results: Plyometric training improved the H:Q ratio while maintaining quadriceps strength in the plyometric group compared to the control group. The women experienced an increase in hamstring strength. Strength gains from plyometric training are based on the fact that stretching a muscle before a contraction leads to greater force production. The reason given in this study for maintenance of quadriceps strength (which would tend to decrease H:Q ratio if it increased) was due to the type of plyometric training they performed. Subjects were not encouraged to jump higher or farther. Instead, proper technique, overall posture and correct take-off and landing positions were emphasized. This focus may have contributed to the strength increases in the hamstrings by placing the hamstrings on stretch during the preparatory and landing mechanics of each exercise. The hamstrings contract eccentrically (lengthening contraction) to stabilize the lower leg when landing.
Practical Application: It is encouraging to know that recreationally-active women were able to safely and accurately perform the plyometric exercises (led by a trained instructor). This type of training can be incorporated into workouts performed in a group setting.