Nonuniform Changes in MRI Measurements of the Thigh Muscles After Two Hamstring Strengthening Exercises
Jurdan Mendiguchia, Mirian A., Garrues, Johm B. Cronin, Bret Contreras, Asier Los Arcos, Nikos Malliaropoulos, Nicola Maffulli, And Fernando Idotate
A review by James Shmagranoff
Introduction
The hamstring muscles are subject to acute injuries in many sports, with the severity of a second injury upon return being much worse than the first. Training the hamstrings eccentrically can develop the strength and size as well as change the optimal length and stiffness of the muscle. The posterior thigh consists of the long and short head of the biceps femoris, the semimembranosus, and the semitendinosus, with each muscle having a specific function and putting emphasis on how to properly introduce rehabilitation after injury as well as creation of strength programs. In order to view the soft tissue activation during exercise along with muscle damage after exercise, functional magnetic resonance imaging (fMRI) can be used as a noninvasive way to further understand what electromyography cannot. To take it a step further, short tau inversion recovery (STIR) shows the tissue differences in water content both intra and intercellularly by utilizing T2-weighted sequences that are positively correlated with plasma creatine kinase activity. This is useful because creatine kinase activity is related to the damage in the muscles. As it pertains to this study, the T2 values of the hamstring muscles differ between proximal and distal regions intramuscularly. No past studies have utilized fMRI for the assessment of intermuscle and intramuscular regional differences in STIR values, so this study will aim to provide knowledge in the signal intensity changes of the upper thigh muscles at 48 hours after a lunge and eccentric leg curl. The hope for these findings is to give insight into injury preventions, strengthening exercise, and rehabilitation of the posterior thigh muscles.
Methods
Experimental approach to the problem: To assess the differences in posterior thigh muscles and locations during the lunge and leg curl exercises of the long and short head of the biceps femoris, the semimembranosus, semitendinosus, and adductor magnus, fMRI was taken both before and after exercise. Randomly with right or left leg, a subject would either leg curl or lunge and then perform the second exercise after the first.
Subjects: Once competition season was over and slowed training had begun, eleven male professional soccer players were offered participation in the study. The men were rejected from the study if they had suffered previous leg injury in a year leading up to the study, were unable to have fMRI due to medical reasons (metallic foreign bodies), or were claustrophobic. The age, height, weight, exercise programming, or previous leg injuries were recorded. To eliminate outside factors the week before the study, the men were to record diet and fluid intake, eliminate lower leg strength training, and stop any icing or anti-inflammatory protocols they were following. All ethics procedures were followed.
Exercise protocol: Lunges and leg curls were randomly assigned to the left and right legs of each subject. The exercises were performed in three sets of six repetitions with two minute rest between sets and then the next exercise for the other leg was performed.
Procedure: The lunges were performed with a specifically marked floor distance, trunk kept upright, both knees bent at the same time, and the trailing knee was lowered to 2-3cm above the ground. The leg curl was performed at 120% their 1RM, determined by failure at 2 reps at a set load, by flexing the knee to 100 degrees and extending to 0 degrees in 3 seconds. Ankles were kept plantar flexed to avoid activating the gastrocnemius. After each eccentric rep, to keep the exercise eccentric only, an examiner raised the weight.
Imaging technique: fMRI was conducted by the same technician on each subject while lying supine with knees extended, legs parallel to the fMRI table, and feet strapped together immediately before exercise and 48 hours post exercise. Fifteen interspaced axial scans (slices) were taken of the thigh at specific anatomical locations for each individual. Signal intensities were used in slices 4-12 of the 15 total slices. STIR images were taken following the fMRI. Standard regions of interest were noted for each participant to obtain baseline signal intensities of each muscle, with blood vessels and bone avoided.
Statistical analysis: The dependent variable in the study was the STIR values of the muscles and the exercise were the independent variable. The purpose was to examine differences in the pre and post exercise STIR values. Paired t-tests determined any significant changes post exercise as well as differences between the two exercises.
Results
Prior to exercise, no significant changes between the right and left leg were found. The semitendinosus had significant changes in STIR values during the leg curl from slices 4-10. Slice 8 showed significant difference during the lunge as compared to before exercise. The adductor magnus had significant changes in slices 4-7 for the lunge, but only in slice 4 for the leg curl. The long head of the biceps femoris had significant differences post exercises in slice 7. No STIR significant changes were found in the semimembranosus and short head of the biceps femoris.
Discussion
STIR values and fMRI were used in this study determine if lunges and leg curl have different outcomes on the thigh’s posterior muscles, and it was found that they do have different responses during different exercises. Because the lunge and leg curl differ in open and closed chain, articulation of the movement, joint moments, concentric components, and the weight bearing load, these factors are left out of the discussion and instead will describe the site-specific activation in each muscle based on the exercise. This information can then be used to determine how to build proper conditioning programming.
The semitendinosus, being the longest fascicle length and smallest cross-sectional of the hamstring muscles, elicits large force productions in large length ranges due to the arrangement of the sarcomeres and their ability to contract simultaneously. While the lunge only elicited change in one slice, leg curls were shown to have the greatest fMRI changes on the semitendinosus, and from this information it can be determined that this muscle is used for efficiency during knee-flexion exercises. Significant differences between the proximal and distal regions of the semitendinosus were found, which is opposing previous research, but may be due to the extensive number of slicing areas utilized in this study as opposed to a lack there of in previous.
The adductor magnus had significant changes in slices 4-7 seen during the lunge. The damage to this muscle during this exercise can be attributed to the fact it is the dominant hip extensor and has superior moment arms at 90 degrees compared to the hamstrings and gluteus maximus. In the leg curl, only one slice had minimal damage and this can be attributed to the angle the hip was placed during this exercise.
The leg curl showed no significant changes in the long head of the biceps femoris, but the lunge (the eccentric movement) in slice 7 showed significant changes. This is similar to other research findings. Both the hip and the knee joint angles contribute to the length of the biceps femoris, but the hip determines the length at a greater impact. The lunge’s impact on the long head of the biceps femoris can be due to internal hip extension moments during hip flexion.
The lunge was shown to have greater proximal activation in slices 5-8, while the leg curl had very minimal and even negative changes in those same slices. The loading of the exercises could be cause for the lack of signal intensity, as it has been shown in past research that heavier loads and exercise intensity will affect fMRI. Future studies will aim for exploration of the effects a loaded lunge can have on the long head of the biceps femoris.
Practical Application
Site specific activation is useful information for strength and conditioning programming as well as therapy. When needing to target the semitendinosus, utilize the leg curl. The lunge is better suited for activation of the long head of the biceps femoris and the adductor magnus.
My interpretation of the findings:
EMG (electromyography) testing and studies are extremely useful in evaluating muscle weakness’s and directly locate areas of dysfunction in which a specific region of a muscle may not be receiving the intended nerve signal. This study utilized functional magnetic resonance imaging (fMRI) to establish the findings as EMG studies cannot always alone determine the root of a clinical issue without further evaluation and testing. The addition of this other noninvasive testing method was a great addition to the study. I am in complete concurrence with the practical application findings from the researchers of this study. This information is truly valuable from a therapeutic standpoint in correcting weakness, or rehabilitating a prior injury. Knowing the extent of activation of specific movements and how slight modifications in posture or joint angles is also an extremely beneficial tool for strength coaches and trainers to know in providing optimal programming to clients and athletes.
References
Mendiguchia, J., Garrues, M.A., Cronin, J.B., Contreras, B., Los Arcos, A., Malliaropoulos, N., Maffulli, N., & Idoate, F. (2013). Nonuniform changes in MRI measurements of the thigh muscles after two hamstring strengthening exercises. Journal of strength and conditioning research, 27(3), 574-581. Retrieved from https://pdfs.semanticscholar.org/b848/7a4339b0a30ff3b0ae24eaa9fd9001c1bde9.pdf
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