Hamstring Studies

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Hamstring strains are one of the most common injuries in sports, especially in those that require rapid bouts of sprinting such as football, track and field, and soccer. Symptoms typically include sudden onset, pain, and tenderness in the posterior thigh region. The combination of slow healing processes along with an extremely high propensity of re-injury leads to missed games and lengthy absences from training, practice, and competition. The purpose of this study is to determine where in the sprinting gait cycle (starting from the starting blocks, initial acceleration, and full speed) muscle force and therefore muscle tension in the hamstring is greatest, and thereby most prone to strain or tearing injury.

 

The subject population will consist of sprinters who practice at least three times a week and are comfortable with starting in starting blocks. Subjects will have reflective markers placed at different anatomical landmarks: acromion, lateral epicondyle of the humerus, wrist (between the styloid processes of the radius and ulna), sacrum (L5-S1), anterior superior iliac spine (ASIS), thigh, lateral knee, shank, lateral malleolus, posterior heel, and at the second webspace (toes). One additional marker will be placed on the upper back on the right side to distinguish left from right during data reduction. In addition, markers will be placed bilaterally at the medial femoral condyle as well as the medial malleolus during a standing trial. These markers will be tracked using an 8 camera Motion Analysis system (Motion Analysis Inc, Santa Rosa , CA ) sampling at 240 Hz.

 

Subjects will be asked to complete 7 trials in each of the following tasks (starting from the starting blocks, initial acceleration (steps 3-4), and full speed sprinting).   During these trials lower extremity kinematic data will be recorded. Subjects will be given a one minute rest between each trial and each trial will be collected at the subject's maximum speed. Once the data has been processed, the results will be entered into a computer model that can be used to determine muscle force production based on lower extremity joint position.

 

Hamstring strains are one of the most common injuries in sports, especially in those that require rapid bouts of sprinting such as football, track and field, and soccer. Symptoms typically include sudden onset, pain, and tenderness in the posterior thigh region. The combination of slow healing processes along with an extremely high propensity of re-injury leads to missed games and lengthy absences from training, practice, and competition. The purpose of this study is to determine where in the sprinting gait cycle muscle force and therefore muscle tension in the hamstring is greatest, and thereby most prone to strain or tearing injury.

 

The subject population will consist of sprinters and middle distance runners who practice at least three times a week. Subjects will have seven sets of surface electrodes attached to their dominant lower extremity. Limb dominance will be determined by asking the subjects to jump on one leg, the leg that they choose will be identified as their dominant limb. The surface electrodes will be placed over the muscle belly of the rectus femoris, vastus lateralis, vastus medialis, semimembranosus, biceps femoris, lateral gastrocnemius, and medial gastrocnemius, with the ground electrode being placed on the tibial tuberosity. Subjects will then have their maximum voluntary isometric contractions (MVIC) recorded while being tested on a Biodex (isokinetic testing device) machine. Subjects will be asked to sit in the Biodex chair at which time their hip flexion angle will be fixed in 80O of flexion. The angle of 80O of flexion was chosen since this is the position of the hip during terminal swing phase, when hamstring injuries are thought to most likely occur.6 Subjects will then be asked to contract their hamstrings against the machine for 5 seconds at the following knee flexion angles: 90◦, 110◦, 130◦, 150◦, and 180◦. The same procedure will be repeated for quadriceps contractions.

 

Following the completion of MVIC collection, subjects will have reflective markers placed at different anatomical landmarks: acromion, lateral epicondyle of the humerus, wrist (between the styloid processes of the radius and ulna), sacrum (L5-S1), anterior superior iliac spine (ASIS), thigh, lateral knee, shank, lateral malleolus, posterior heel, and at the second webspace (toes). One additional marker will be placed on the upper back on the right side to distinguish left from right during data reduction. In addition, markers will be placed bilaterally at the medial femoral condyle as well as the medial malleolus during a standing trial. These markers will be tracked using an 8 camera Motion Analysis system (Motion Analysis Inc, Santa Rosa , CA ) sampling at 240 Hz.

Prior to data collection, subjects will be given a standard speed at which to complete the running trials; men at 7.25 m/s ± 5% and women at 6.0 m/s ± 5; subjects will complete 5 trials at that speed. During these 5 trials both kinematic and EMG data will be recorded. Once data collection is completed at the standard speed, the subjects will then be given a 5 minute rest before they are asked to run 5 trials at their maximum speed. Once the data has been processed, the results will be entered into a computer model that can be used to determine muscle force production based on joint position and muscle activation as recorded from EMG activation and lower extremity kinematics.

 

Publication Status:

 

 

Bing Yu, Robin M. Queen, Alicia N. Abbey, Yu Liu, Claude T. Moorman, William E. Garrett. Hamstring Muscle Kinematics and Activation During Overground Sprinting. Journal of Biomechanics. 41: 3121-3126, 2008.

Hamstring strains are one of the most common injuries in sports, especially in those that require rapid bouts of sprinting such as football, track and field, and soccer. Symptoms typically include sudden onset, pain, and tenderness in the posterior thigh region. The combination of slow healing processes along with an extremely high propensity for re-injury leads to missed games and lengthy absences from training, practice, and competition. Most hamstring strains are thought to occur during eccentric muscle activation and many predisposing factors have been linked to hamstring injury, including inadequate flexibility, muscle fatigue or weakness, insufficient warm-up, previous injury, and poor running technique. Rehabilitation and therapy have been shown to produce a sustained shift in optimum angle of human muscle as a protective strategy against injury through eccentric rehabilitation exercises.

Low hamstring strength could result in the forces necessary to resist knee extension and start hip extension during maximal sprints to surpass the tolerance of the muscle-tendon unit. Ultimately, effective strengthening of the hamstrings is vitally important to lowering the predisposition to injury. Both isometric and isokinetic specific exercises have been shown to be successful within their own subtypes, but effectiveness has been limited when looking at cross-over between isometric and isokinetic strength changes. Kaminski et al. also found that eccentric strength training was more effective than concentric strength training on peak isokinetic eccentric hamstring torque. The Nordic hamstring curl could potentially be an effective exercise to strengthen the contractility of the hamstring both isometrically and isokinetically. Such a strategy may be able to increase the working range of the muscle in relation to its length-tension curve, and prevent fibers from reaching a length where they are susceptible to tearing. A recent study compared the traditional concentric hamstring curl to the eccentrically-focused Nordic hamstring curl in competitive soccer players. The Nordic group showed an 11% increase in eccentric hamstring torque at 60 degrees, as well as a 7% increase in isometric hamstring strength at 30, 60, and 90 degrees of knee flexion, while no changes were observed in the traditional hamstring curl group.

 

A total of 60 subjects will be tested, with an equal number of men and women. Subjects will range in age from 18-30 years. All subjects will be evaluated in a pre-training phase: they will have surface electrodes attached to their dominant lower extremity. Limb dominance will be determined by asking the subjects to define their “kicking leg” and “planting leg”. We will choose the “planting leg” as the dominant leg. Once electrode placement has been verified, the electrodes will be wrapped onto the subject’s leg using prewrap and a small amount of athletic tape. Subjects will then have their maximum voluntary isometric contractions (MVIC) recorded while being tested on a Biodex (isokinetic testing device) machine. Subjects will be asked to contract their hamstrings against the machine for 5 seconds at the following knee flexion angles: 90, 110, 130, 150, and 180 degrees. In addition, subjects will be asked to complete two maximum quadriceps contractions at 130 degrees and two maximum isometric contractions of the gastrocnemius. The subjects will then be asked to complete 5 trials of isokinetic concentric hamstring curls at 60 degrees/second and 5 trials of eccentric isokinetic hamstring curls both in the range from 90 to 180 degrees of knee flexion. The subjects will then be asked to complete 5 Nordic hamstring curls while both muscle activation as well as angle of inclination relative to the ground are recorded.

 

 

Subjects will be divided into males and females and then into 3 groups - one Nordic curl training group, one open-chain hamstring weight-lifting curl group, and one control group without a hamstring strengthening protocol. The groups will be followed for 4 weeks. The Nordic curl training group will perform 2 sets of 10 Nordic hamstring curls 3 days per week while being monitored in the lab for appropriate technique, while the control group will make no change to their daily exercise. The open-chain hamstring weight-lifting curl group will also perform 2 sets of 10 hamstring curls 3 days per week while being monitored in the lab for appropriate technique. Depending on exercise performance of each participant, we may allow independent performance of the exercises after a full 2 weeks of close monitoring. All participants will be contacted by telephone or e-mail on a weekly basis to remind them of their commitment to come to the lab or to perform the exercises independently. Upon completion of the 4 week period, both groups will be retested using the prior protocol.

 

 

Current Status:

The article is currently being prepared for submission