Architectural differences between the hamstring muscles

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Abstract

The purpose of this study was to understand the detailed architectural properties of the human hamstring muscles. The long (BFlh) and short (BFsh) head of biceps femoris, semimembranosus (SM) and semitendinosus (ST) muscles were dissected and removed from their origins in eight cadaveric specimens (age 67.8 ± 4.3 years). Mean fiber length, sarcomere length, physiological cross-section area and pennation angle were measured. These data were then used to calculate a similarity index (δ) between pairs of muscles. The results indicated moderate similarity between BFlh and BFsh (δ = 0.54) and between BFlh and SM (δ = 0.35). In contrast, similarity was low between SM and ST (δ = 0.98) and between BFlh and SM (δ = 1.17). The fascicle length/muscle length ratio was higher for the ST (0.58) and BFsh (0.50) compared with the BFlh (0.27) and SM (0.22). There were, however, high inter-correlations between individual muscle architecture values, especially for muscle thickness and fascicle length data sets. Prediction of the whole hamstring architecture was achieved by combining data from all four muscles. These data show different designs of the hamstring muscles, especially between the SM and ST (medial) and BFlh and BFsh (lateral) muscles. Modeling the hamstrings as one muscle group by assuming uniform inter-muscular architecture yields less accurate representation of human hamstring muscle function.

Introduction

The hamstring muscle group consists of the semimembranosus (SM), the semitendinosus (ST) and the long head of the biceps femoris (BFlh). The short head of the biceps femoris (BFsh) is a mono-articular muscle which shares a common tendon with BFlh and it is frequently examined alongside with the hamstrings. Since architecture affects significantly the force generation capacity of each muscle, studying hamstring muscle function in vivo often requires modeling of their architectural properties (Thelen et al., 2005, Chumanov et al., 2007). Such models are applied for the estimation of muscle and tendon length in subjects with cerebral palsy (Arnold et al., 2006), for the examination of hamstring injury potential in athletes (Thelen et al., 2005, Chumanov et al., 2007), for the improvement of ST tendon grafts for surgical reconstruction of anterior cruciate ligament (Pichler et al., 2008) or for the prediction of hamstring muscle forces based on electromyographic (EMG) signal recordings (Kellis and Katis, 2008a, Kellis and Katis, 2008b).

Numerous studies on whole body muscle architecture have reported that the hamstrings have relatively longer fibers and a lower physiological cross-sectional area (PCSA) than many other human muscles and therefore they are considered as muscles designed primarily for excursion (Alexander and Vernon, 1975, Wickiewicz et al., 1983, Friederich and Brand, 1990, Woodley and Mercer, 2005, Klein Horsman et al., 2007, Ward et al., 2009). Latest studies have reported large intra-muscular and inter-muscular variations in morphology of the hamstrings (Chleboun et al., 2001, Woodley and Mercer, 2005, Kellis et al., 2009, Kellis et al., 2010). For example, Kellis et al. (2010) reported considerable proximo-distal differences in ST and BF architecture which probably has an effect on their force–length and force–velocity properties. However, this study examined only two hamstring components while no inter-muscular comparisons were performed.

Estimation of muscle forces often requires modeling of the hamstring muscle group. In many cases hamstring moment is predicted by assuming that one muscle component is representative of the knee flexor muscle group (Kaufman et al., 1991, Lutz et al., 1993, Escamilla et al., 1998, Kellis et al., 2005). However, because individual muscles differ in size and architecture, their relative contribution to the force exerted by the whole muscle group might differ, and this might be an error source of the modelling process. In other cases, the problem of moment sharing between different synergists is examined by using electromyography (EMG) measurements in combination with physiological and anatomical characteristics of each muscle (Lutz et al., 1993, Dowling and Cardone, 1994, Dowling, 1997, Escamilla et al., 1998, Zheng et al., 1998). However, research studies have failed to report consistent evidence on similarity or differences in EMG activity between these components (Kaufman et al., 1991, Escamilla et al., 1998, Fiebert et al., 2001, Mohamed et al., 2003). Therefore, the contribution of each component to the force exerted by the whole hamstring muscle group is not clear yet.

Since the hamstring muscle group is activated around two joints (the hip and knee), there is a requirement for considerable force generation which must accommodate large changes in joint range of motion, especially when the hip and knee change position simultaneously (Chleboun et al., 2001). This may be one reason for the existence of several muscles acting synergetically as a group, each, however, having a different architecture (Jacobson et al., 1992, Lieber et al., 1992a, Lieber et al., 1992b, Lieber, 1997). For example, the ST muscle has a parallel fiber configuration while BFlh and SM are pennated (Alexander and Vernon, 1975, Wickiewicz et al., 1983, Friederich and Brand, 1990, Woodley and Mercer, 2005, Klein Horsman et al., 2007, Ward et al., 2009). The ST and BFsh muscles have much longer FL than the rest hamstring heads while the SM displays the highest PCSA (Woodley and Mercer, 2005). Further, the ST and SM (medial hamstrings) run medially along the thigh and have different distal attachments compared with the BFlh and BFsh (lateral hamstrings). In addition, large differences in moment-arms (An et al., 1984, Spoor and Van Leeuwen, 1992, Herzog and Read, 1993) between hamstring muscles have been reported. Such variations would have an effect on the force-generation capacity of each hamstring muscle and, in turn, on their synergetic function so that a common force is exerted, at least around the knee joint. Information on hamstring muscle architectural variables is available from studies investigating whole body muscle architecture (Alexander and Vernon, 1975, Wickiewicz et al., 1983, Friederich and Brand, 1990, Woodley and Mercer, 2005, Klein Horsman et al., 2007, Ward et al., 2009). However, detailed examination of inter-muscular variations of this particular muscle group is currently missing.

The purpose of this study was to examine differences in architecture between the hamstring muscles. Two hypotheses were examined. First, how architecture of one hamstring muscle is related to the architecture of the rest muscles and second, whether examination of architecture of one muscle component can be representative of whole hamstring architecture.

Section snippets

Study design

Hamstring muscle architectural data from one leg was obtained from eight human cadavers (males) with a mean age of 67.8 (±4.2 years) and height of 167.3 (±2.3 years). All cadavers had no lower extremity pathologies prior to death. The cause of death was heart attack (2 cadavers), cancer (5 cadavers) and brain stroke (1 cadaver). The protocol was approved by the Aristotle University Ethics Committee.

Each cadaver was embalmed in anatomical position with the hip and knee angles at 0° (full

Results

Muscle architecture data are presented in Table 1 while length measures are presented in Table 2. The results indicated low to moderate similarity (δ < 0.80) for comparisons between muscles (Table 3). The highest similarity was between BFlh and SM and the lowest between BFlh and ST.

The correlation coefficients between z-scores of all four muscles are presented in Table 4. The results showed high inter-correlation in MT, when equal ratio was used. In contrast, when MT values were adjusted for

Discussion

The main findings of this study were that (a) the four hamstring components show low to moderate architectural dissimilarity (b) there are moderate to high inter-muscular correlations in each architecture variable and (c) best prediction of whole hamstring architecture requires evaluation of all muscles’ architecture.

The results showed a low to moderate architectural similarity between the hamstring muscles (Table 3). In fact, only the BFlh and SM showed an index value (δ = 0.35) which almost

Eleftherios Kellis is an associate professor in Sport Kinesiology at the Department of Physical Education and Sports Sciences at Serres, Aristotle University of Thessaloniki, Greece. He obtained his B.Ed. in Physical Education and Sport Sciences, at the Aristotle University of Thessaloniki, Greece (1993) and his Ph.D. at the Department of Movement Sciences and Physical Education, University of Liverpool, United Kingdom (1996). He has many research publications while he authored a book entitled

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Eleftherios Kellis is an associate professor in Sport Kinesiology at the Department of Physical Education and Sports Sciences at Serres, Aristotle University of Thessaloniki, Greece. He obtained his B.Ed. in Physical Education and Sport Sciences, at the Aristotle University of Thessaloniki, Greece (1993) and his Ph.D. at the Department of Movement Sciences and Physical Education, University of Liverpool, United Kingdom (1996). He has many research publications while he authored a book entitled “Neuromechanical principles of human muscle strength assessment” in 2008. He is a co-founder of the Laboratory of Neuromechanics at Serres, Greece and his main research interests include hamstring muscle modelling and function, joint mechanics and clinical electromyography applications.

Nikiforos Galanis has a B.Ed. in Physical Education and Sport Science (1993), a Bachelor degree in Medicine and a Ph.D (2002) from the Medical School of the Aristotle University of Thessaloniki, Greece. He also graduated from the London College of Osteopathic Medicine, U.K while he has served as hospital practitioner and research fellow at University College of London, NHS (U.K). He is an assistant professor in exercise physiology at the Medical School of the Aristotle University of Thessaloniki, Greece. His research interests include clinical physiology and orthopaedic applications, with emphasis on muscle biopsies and blood flow distribution and exercise.

George Kapetanos is a professor in orthopaedics and head of the Orthopaedic University Clinic of the Papageorgiou hospital, Aristotle University of Thessaloniki, Greece. He completed his undergraduate studies in Medicine at the National Kapodestrian University of Athens, Greece and he obtained his Ph.D. from the same faculty. He has very long teaching, clinical and research experience. He has many research publications and he has written several basic textbooks in orthopaedics and related fields. He has served the field of orthopaedics in Greece from various posts, such as, being president of the Hellenic Association of Orthopaedic Surgeons and Traumatology (2002) as well as of the Hellenic College of Orthopaedic Surgeons (2009-10). Among his research projects in the field of orthopaedics, his greatest interest is on spine biomechanics.

Konstantinos Natsis is an orthopaedic surgeon and an associate professor in Anatomy at the Medical School of the Aristotle University of Thessaloniki, Greece. He has a B.Ed. in Physical Education and Sport Science (1986), a Bachelor in Medicine and a Ph.D (1993) from the Medical School of the Aristotle University of Thessaloniki, Greece. He is the director of the Laboratory of Anatomy and he has many research publications in anatomy and orthopaedic related issues. Dr Natsis has served as president of the Northern Hellenic Association of Sports Medicine while he is an active member of many international societies in sports medicine and orthopaedics. His research interests include descriptive anatomy applications as well as exercise effects on muscle morphology and function.

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