Sports Medicine Research: In the Lab & In the Field: The Use of Plyometrics to Improve Q:H Strength Ratio (Sports Med Res)


Wednesday, October 12, 2011

The Use of Plyometrics to Improve Q:H Strength Ratio

Improving the Q:H Strength Ratio in Women using Plyometric Exercises

Kavin Tsang and Angela DiPasquale, J Strength Cond Res. 2011 Oct; 25(10): 2740-5.

Since the initiation of Title IX in 1972 female participation in sports has increased. Over time the increased level of participation and level of competition has contributed to a larger incidence of injury among women, particularly injury to the anterior cruciate ligament (ACL). Several factors contributing to the increased rate of injury have been evaluated. A primary area of focus has been strength imbalances of the quadriceps and hamstring muscles measured as Q:H strength ratio. Previous literature has found that females demonstrate a lower Q:H strength ratio compared to males, and a lower Q:H strength ratio in the ACL injured leg compared to the uninjured leg. The purpose of this study was to evaluate the Q:H strength ratio in female subjects after 6 weeks of plyometric training compared to age matched healthy control subjects. Twenty-five female subjects participated in this study (11 plyometric, 14 control) consisting of isokinetic testing at baseline, 2, 4 and 6 weeks during the training program for knee flexion and extension at 60 and 120°/sec. The plyometric subjects participated in training 3 days a week for 6 weeks, involving 7 of 13 possible lower extremity plyometric exercises; control subjects did not. The training program was adapted from a previously established program by Hewett et al, consisting of exercises such as tuck jumps, scissor jumps, squat jumps and 180 jumps. The training sessions were led by the primary investigator who explained and demonstrated each exercise. Focus on proper technique, and correct take-off and landing mechanics was stressed. The results demonstrated a significant difference over time in the plyometric training group for hamstring strength at 120°/sec (Avg Power, PeakTorque). There was no significant different between the plyometric group and the control group at any time during the training sessions for quadriceps strength measures at 120°/sec. No significance was seen for either quadriceps or hamstring strength at 60°/sec in all participants. These findings demonstrate that over time, this plyometric training program increased hamstring strength, while maintaining quadriceps strength. This trend in strength allows for an improved Q:H strength ratio.

Muscle imbalance is thought to be a risk factor for ACL injury, particularly in females. Improving the Q:H strength ratio has the potential to decrease the risk for ACL injury. These strength improvements were only seen during isokinetic testing at higher speeds (120°/sec). This suggests that eccentric plyometric training improved hamstring strength for more rapid, dynamic tasks only. Emphasis of this training program was placed on proper mechanics and technique instead of intensity of exercise such as increasing the jump distances and height which might have allowed for a change in strength when tested at 60°/sec. I am not surprised by the results of this study. Over 10 years ago Hewett et al found that plyometric training influenced landing kinetics in female athletes. The next question is, “Does plyometric training decrease the risk for ACL injury?” A review of the literature by Grindstaff et al determined that 89 people needed to complete preventative plyometric training to prevent 1 ACL injury within a single sports season. Yes, plyometric training improves Q:H strength ratios, but does that decrease the risk of ACL injuries? Should all young female athletes participate in prophylactic plyometric training?

Written by: Kathleen White
Reviewed by: Stephen Thomas


Whitney M said...

This was an interesting study and I would also be interested in whether plyo metric training decreases the risk of ACL injuries in females. Because plyo metrics are used for strength and speed training, many of the sports where ACL injuries are prevalent (i.e. soccer), would benefitl for this training to possibly be prophylactic in preventing ACL injuries but also other sport related improvements (speed). Plyometric training could still be implemented as part of training, even if it was only in preseason.

Kathleen White said...

Thanks for your comment Whitney.

The study by Grindstaff et al, referenced in the review, determined the number needed to treat to prevent an ACL injury. They only included studies in their literature review that examined female athletes that had undergone plyometric training. Each individual study included in this review demonstrated decreased injury rates among the plyometric intervention group compared to their control groups.

This suggests that the use of plyometric training can reduce the risk of ACL injury in female athletes, but it can not prevent all ACL injuries.

Several recent studies by Meyer et al (, ( have evaluated when the best time is to implement plyometric training in all young athletes. The use of plyometric training has branched out to all athletic populations in an effort to reduce all athletic injuries.


Eunwook said...

I agree with the plyometric exercise actually helps to improve Q:H ratio because of increasing hamstring strengthening and I would use plyometric exercise as prophylactic injury prevention training program because of various benefits from the exercise.. However, the problem of Q:H ratio itself is that it measures relative value of muscle strength. Personally, I think that the quadriceps strength is the fundamental factor to prevent any knee joint injury. If a person has relatively weak quadriceps muscle strength for any reason (ex: muscle inhibition or previous injury), it might seem like a good Q:H ratio. But I would say that we should consider actual quadriceps and hamstring strength level of a person before to see only Q:H ratio. Plyometric exercise itself has a lot of benefits not just only performance but injury prevention. Specially, co-activation of quadriceps and hamstring muscle during plyometric exercise would be one of the important effects. As a clinician, I would like to do this exercise technique as prevention injury program.

Kathleen White said...

Thanks for your comment. I agree with your statement that the Q:H ratio doesnt always give up the entire picture of a patients strength. That is similar to Quadriceps Index (QI). It is a relationship of how strong the quads are between legs of the same person. However if the uninjured leg is weak as well as the injured leg then you will get a deceivingly high QI value. Raw values to compare these measures will show a better picture of the persons strength.

Thanks for bringing that up, it is a great point to remember!

Warren Potash said...

I agree that the Q:H is not the be all for positive results for all female athletes. First time female athletes for training to play sports have consistently fallen in the 38% to 42% Q:H for baseline testing. I have never had a teen female athlete exceed 51% at the conclusion of their training in my 13 week program and I have achieved tremendous results. What I call BNP Training [stabilize and strengthen the lower body] takes place throughout the training with plyometrics introduced in the last 4 weeks. I have used this approach for the past 16 years. Therefore, I believe that all female athletes, not just the elite, need to value training to play sports with safe and age-appropriate training programs; 9 to 13 weeks provides the best results. The functional/integrated approach has worked very well for more than 600 teen female athletes from every sport and cheering. Q:H is one measure that I assess, but it can never stand alone in sport-specific training for female athletes.

Kathleen White said...

Thats for your comments Warren. It sounds like you have a great training program for these female athletes. Its wonderful to hear such positive results.

There seems to be a common theme in all of the posts. The Q:H ratio is just one measure that we assess and alone it will not be able to provide a true picture of an athletes status.

Jay Clark ATC said...

I think that another thing we should consider is the prevalence of ACL injury. Q:H ratio is a commonly used predictor of ACL rupture/injury, but still the prevalence of the injury is quite low.

The Grindstaff study found that 89 athletes would need to undergo this program to prevent 1 injury, but on a full varsity high school roster of 22 athletes, you would be preventing one injury about every four seasons.

Epidemiological studies have placed ACL injury to occur in about 1.5% of athletes, so I would consider this program to be of some value when it comes to preventing ACL rupture.

This being said, I still feel that this prevention program is just one tool to the healthier participation, and a larger number of other possibilities can be used to help athletes compete successfully and safely.

Thanks for posting this!

Kathleen White said...

Thanks for your comment Jay!

Its great to hear continued support of these ACL prevention programs. You bring up a great point that these programs are not the only way to protect these athletes. The demands of each sport are different and one standardized program will not benefit all athletes.

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