Muscle Imbalances: Testing and Training Functional Eccentric Hamstring Strength in Athletic Populations

The hamstrings are a group of muscles that are sometimes problematic for athletes, resulting in soft tissue injury in the lower limbs. To prevent such injuries, functional training of the hamstrings requires intensive eccentric contractions. Additionally, hamstring function should be tested in relation to quadricep function at different contraction speeds.

The overall goal of this protocol is to measure the functional quadricep to hamstring ratio, determine the force angle curve of knee flexors and extensors, and identify possible muscle asymmetries at different movement speeds. This method can show how the hamstring functions and hamstring to quadriceps ratio change with the speed of movement. The main advantage of this technique is the ability to compare eccentric hamstring actions to concentric quadriceps actions.

The implication of this technique extends toward a comprehensive diagnostic and the results can be easily transferred into ongoing resistance training programs. Dusan Blazek, a strength and condition coach, is going to perform isokinetic test protocol. Before participating in official testing, familiarize the qualified subject with eccentric isokinetic testing on a valid isokinetic dynamometer at least twice.

Instruct the subject not to perform any lower body resistance training or other strenuous exercises 72 hours before testing. To begin the procedure, guide the subject through a general warmup. Instruct them to jog for five to 10 minutes or cycle for five to 10 minutes on an ergometer with a resistance of 1.5 to two watts per kilogram of body mass with a cadence between 60 and 90 rpm.

After cycling, instruct the subject to perform two sets of eight to 10 body weight lunges and eight to 10 hamstring curls on a Swiss ball with each leg with one minute of rest between sets. Next, guide the subject through dynamic stretching of the lower limbs including the quadriceps and hamstrings. Show the subject an example of the isokinetic torque angle curve and explain that live visual feedback will be provided during the test.

Explain that the subject should kick out as hard and fast as possible for concentric knee extension and pull back as hard and fast as possible for concentric knee flexion. Also explain that the machine will move on its own during eccentric actions, but that the subject should try to push as hard as possible during eccentric knee flexion and pull as hard as possible during eccentric knee extension. The subject has to be specifically instructed to expect the dynamometer push or pull during the eccentric test and the subject should not lessen the force production when the eccentric movement happen.

Allow the subject to ask any questions and make sure they understand what will happen during the test. Clearly state that if the subject experiences any pain or discomfort during the test that makes him or her wish to terminate the test at any time, he or she should inform the researcher immediately and the test can be safely aborted. Now start the preset protocol and continually guide the subject through the protocol.

Guide the subject on the dynamometer in a sitting position with a hip angle of 100 degrees of extension. Then adjust the settings of the dynamometer to ensure that the subject's hips are all the way back and in contact with the chair and the dynamometer's axis of rotation is in line with the axis of rotation of the subject's tested knee. Instruct the subject to hold a deep breath while fixing the shoulders, pelvis, and thigh of the tested leg using the pads and straps on the dynamometer.

Fix the lever arm of the dynamometer to the distal part of the shin with the pad placed 2.5 centimeters over the apex of the medial malleolus, but do not support the non-exercised lower limb. Allow the subject to passively and actively go through the full extension and flexion range of motion while readjusting the straps, dynamometer settings, or both if needed. Next, ensure that the subject can see a screen that shows the torque angle curve and provide a verbal countdown to begin the test.

Instruct the subjects to hold the hand grips located at the side of the seat during all testing efforts. Start the test and verbally encourage the subject by using phrases such as go, push harder, and pull, pull, pull. During the rest intervals, provide the subject with short instructions about the upcoming task.

After completing the protocol, allow the subject to get out of the dynamometer chair and adjust the dynamometer to test the other limb. After repositioning the subject and adjusting the machine accordingly, perform the gravity correction measurement again and start the test for the untested lower limb. Subsequently, open the test results that show the angle torque curve and check whether the subject achieved the selected speed of contraction for the whole movement.

Immediately after testing, you should check to see if the force angle curve is interrupted. To determine if the desired speed was accomplished, ensure that the angle torque curve does not appear to be interrupted. If the curve looks interrupted, it is likely that the subject did not push or pull against the lever arm fast enough for the dynamometer to register torque.

If the subject was not able to reach the required angular velocity and register torque, continue with additional familiarization or exclude the subject from the study and check the possibility of an articular knee lesion. This figure shows an example of appropriate knee flexor and extensor torque during 10 to 90 degree of knee flexion range of motion. This figure represents the torque angle strength curve for knee extension and this figure represents the torque angle strength curve for knee flexion.

Shown here is an example of an interrupted torque curve during 10 to 90 degree knee flexion range of motion. This figure represents the torque angle strength curve for knee extension and this figure represents the torque angle strength curve for knee flexion. This figure shows the representative results of the hamstring to quadriceps functional ratio with and without specific hamstring training where pre EHT represents Eccentric Hamstring Training group results before specific eccentric hamstring training and post represents test after 12 weeks specific training.

The maximal attainable torque is highly dependent on the speed of contraction, meaning that it is crucial to check whether an athlete can generally torque against the lever arm for the whole range of motion during the high speed protocol, for example 240 degrees per second.