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

Summary

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.

Abstract

Many hamstring injuries that occur during physical activity occur while the muscles are lengthening, during eccentric hamstring muscle actions. Opposite of these eccentric hamstring actions are concentric quadriceps actions, where the larger and likely stronger quadriceps straighten the knee. Therefore, to stabilize the lower limbs during movement, the hamstrings must eccentrically combat against the strong knee-straightening torque of the quadriceps. As such, eccentric hamstring strength expressed relative to concentric quadricep strength is commonly referred to as the "functional ratio" as most movements in sports require simultaneous concentric knee extension and eccentric knee flexion. To increase the strength, resiliency, and functional performance of the hamstrings, it is necessary to test and train the hamstrings at different eccentric speeds. The main purpose of this work is to provide instructions for measuring and interpreting eccentric hamstring strength. Techniques for measuring the functional ratio using isokinetic dynamometry are provided and sample data will be compared. Additionally, we briefly describe how to address hamstring strength deficiencies or unilateral strength differences using exercises that specifically focus on increasing eccentric hamstring strength.

Introduction

The relationship between knee flexor and extensor strength has been identified as an important parameter in assessing a person's risk of incurring a lower limb injury¹. Specifically, there is an increased probability of hamstring injury when ipsilateral or bilateral imbalances in hamstring strength are present when compared to quadricep strength². Therefore, many sport scientists and practitioners test knee flexor and extensor strength to determine whether an athlete is at risk of incurring a hamstring injury. However, various testing methods are used that do not allow for direct comparisons to be made between method....

Protocol

The presented protocol follows the guidelines of human research ethics committee at Charles University, Faculty of Physical Education in Sport and has been previously approved as part of research.

1. Familiarize All Subjects Before Isokinetic Testing by Following Steps

1. Ensure that the subjects have not had any recent musculoskeletal injuries or pain in the lower limbs in the previous 6 months. If a subject reports recent knee pain, or has knee pain during testing, exclude the subject.
2. As eccentric isokinetic testing is likely a novel stimulus for many individuals, familiarize the subject with the protocols on a valid i....

Results

The examples below show the differences between young elite soccer athletes (age 15.4 ± 0.5 years, body mass 62.7 ± 8.2 kg, height 175 ± 9.1, training experience more than 8 years) performing eccentric hamstring training (EHT, n = 18) and without EHT (n = 15) for 12 weeks (Figure 3). The group performing EHT included this exercise two times per week, while the group without EHT performed core training and a general lower limb program instead. Both groups part.......

Discussion

The first critical step in the aforementioned protocol is the athlete's familiarization, especially for the eccentric tests. Subjects may have to be familiarized two or three times to ensure reliable data during such isokinetic testing. Furthermore, it may be a good idea to re-familiarize subjects if testing sessions are more than two months apart. The second critical step is properly setting up the athlete in the dynamometer, ensuring that the knee axis is in-line with the axis of the dynamometer; it is also importa.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
HumacNorm	CSMI, Stoughton, MA, USA	021-54412236 (model 502140)	Standard Dynamometr
SoftwareHumac 2015	Computer Sports Medicine Inc. Stoughton, MA, USA	Version155	Software for dynamometr