Muscles Compartments and their relative strength - Article Example

?Muscles Compartments and their relative strength, are their muscle-tendon units optimized for their minimum mass? K.W. Fok1, K.M. Mah1, J. Hales1 School of Biomedical Science, University of Queensland, Brisbane St Lucia, QLD 4072 Abstract The aim of this study is to assess the muscles in their particular compartments; based on the differences in muscle architecture, and strength of the leg muscles. The relationship between muscle architecture variables and strength was analyzed, as well. Participants in this study included cadavers randomly assigned to different groups. Skeletal muscles architecture was visualized during the dissection process. Attention was given to muscle thickness, fascicle length, and force development. This study is focused in testing the hypothesis of Ker at al. (1988) in relation to muscle-tendon units optimized for minimum mass. Data was collected and analyzed from allocated cadavers. The relative strengths of muscles as well as the associated functions of muscle compartments are also analyzed in this study. KEYWORDS: Muscle, muscle architecture variables, biomechanics, fascicle length Introduction A muscle-tendon unit (MTU) is the force produced by a muscle reacting reciprocally to its linked tendon; it functionally assists the body in actions like locomotion. (Finni, 2006)(Magnusson, 2003) Contractile components of a MTU is not the only factor contributing to force production, the elastic components play a role in producing force as well (Finni, 2006)(Wang, 2006). Due to its elasticity, the elastic components have the ability to recoil. This characteristic of tendon allows storage of energy that can be better exploited for efficacy of contraction of muscles, or reduction in “muscle-tendon power” due to absorption of energy (Richards & Sawicki, 2012). Tendon stretches during muscle contraction and the more a tendon stretches the higher the strain of the tendon (Wang, 2006). This stretch accumulates elastic recoil energy until it is released or tears due to reaching maximal strain, this relates to the stress-strain curve (Wang, 2006). Tendons vary in size and thickness and might be related to the type of movements produced (Magnusson, 2003), with more endurance type of movements in a certain muscle can cause hypertrophy of the tendon (Magnusson, 2003) (Woo et al., 1982). A muscle’s architecture has been a part of various studies. Tendons connect muscles to bones; necessitating essential functions in force transfer from contracting muscle fibers to the bone, and force transmission. Studies have also reported tendons capability of reducing locomotion (Biewener and Roberts, 2000; Lichtwark et al., 2007a-b; Lichtwark and Barclay, 2010). According to a study done by Wickiewicz, Roy, Powell, Perrine, & Edgerton in 1984, muscle architecture has been reported to influence its contraction properties because fibre length and pennation angle are closely associated with differences in muscle shortening velocity (Wickiewicz et al, 1984: Izquierdo et al., 1996: Young & Bilby, 1993). Ker et al. (1988) used a variety of materials in their study all derived from human cadavers. They used human leg muscles and their tendons. In this paper, a report will be made concerning measurements of area ratios for the muscles of the right lower limb. Calculation of the relative strengths of the muscles and muscle compartments will also be studied. Materials and methods This study was performed on the right lower limb of a male, aged 90 years, cadaver number 4239. His cause of death was multi infarct dementia; cerebrovascular disease; hyperlipidemia. The lower and upper limbs seemed healthy but frail. Isometric and dynamic explosive force production of leg extensor muscles varies in men at different ages. The younger the age, the more strength the muscle possesses (Ha?kkinen et al, 1996). Tendon samples were obtained from the limbs of the cadavers. The first procedure was to identify the muscles, sites of origin, insertion, and the position of the limb recorded. The muscles and tendons were dissected out in turns with careful dehydration precautions taken. This was achieved by the application of Propylene Glycol evenly on all exposed parts of the cadaver after exposure of 10-15minutes while Citricidal Topical Spray (Anti-Mould Agent) was applied throughout the cadaver after exposure for dissection. Surfacide in Water 20% concentration was the cleaning disinfectant used. Equipment, body bag and surfaces of dissection tables were sprayed down and wiped after every dissection session. The total length of muscle was measured with a ribbon. This was done by placing the ribbon closely along the length of the muscle from the origin to the insertion point of each respective and corresponding muscle. The length as marked off from the ribbon was then measured with a ruler and recorded. A measured length cut from each tendon was weighted and it’s cross sectional area calculated from its length and mass. The belly of each muscle was weighed and then cut out into the plane of its fascicles. The muscle belly length of the muscle was measured by placing the ribbon along the length of the muscle belly from the origin to the junction where the tendon first appears. The length as marked off from the ribbon was then measured with a ruler and recorded. Fascicle length was measured from tendon of origin to the tendon of insertion in several parts of the muscle. The overall tendon length was measured by placing the ribbon along the length of the tendon from the insertion point to the junction where the muscle belly first appears. The length as marked off from the junction was marked off from the ribbon and measured with a ruler. The moment arm around each of the joints that the muscle passes around was measured. The perpendicular length from the tendon to the axis of rotation of the joint was marked off with ribbon and measured with a ruler and recorded. The muscle belly, along with the distal end of the tendon was removed by dissecting as close to the point of origin and insertion as possible. A uniform – width section of the tendon was observed from the dissected muscle along with the far end of the tendon and an ideal length between 5cm to 7cm was measured, cut and recorded. The segment of between 5cm to 7cm of tendon was weighed on a weighing scale with the perimeter of 0.01g to 10g. External tendinous material were removed from the muscle belly and weighed on a weighing scale with the perimeter with regards to muscle belly mass of the leg. The muscle fascicle length was determined by the following steps: The collagenous tissue along the tendon was first cut and separated to two parts. Following that, a muscle fibre was isolated with a shallow cut along its length made by a scalpel. The length of the isolated fascicle was then measured with a ruler and recorded. Triplicates of fascicle lengths were taken from three different parts of the whole muscle belly and recorded. Triplicates of isolated fibres were used to measure the fascicle angle with a protractor. Triplicates of a small group of fibre specimen were obtained from three different parts of the muscle belly and placed on a microscopic slide. Following, a drop of glycerol jelly (mounting media) was dropped on each of the specimen and covered with a cover slip. Slides were kept aside for observation under the microscope and subsequent determination of sarcomere spacing Statistical Analyses According to Yamaguchi et al. 1990, equation A5; the physiological cross-sectional area (PCSA) of a muscle is: PCSA= (m/pl) cos?. Where m is the muscle belly mass, p its density, l is the mean fascicle length and ?, the angle of pennation. If the angle of pennation is small, its physiological cross sectional area is roughly (m/pl), and its cosine is close up to 1.00. Incorporating studies from Mendez and Keys, 1960 brings about a related equation. As shown below: PCSA= {M * Cos (PA)} / {p * FL} Whereby PA is the pennation angle, FL fibre length. Fascicle length was estimated as the length of the hypotenuse of a triangle with an angle equal to the pennation angle, and the side opposite to this angle equal to the muscle thickness, by the following equation: Fascicle length= Muscle thickness/sin (pennation angle) Tendon length was determined by total length of the tendon. This can be shown the equation below: TL (tendon length) = ETL (external tendon length) + ITL (internal tendon length). The results are expressed as means ± standard deviation. Relationships between selected variables; that are strength, fascicle length and optimum mass were examined. Evaluation of the relationship among these variables was made possible by using Pearson product – moment correlations as well as ANOVA method. ANOVA method was relevant in comparing the relationships of the variables. Results Masses and fascicle lengths were determined for 14 muscles. The one-way ANOVA multiple comparison tables for was significantly different compared to the hypothesis of Ker et al. (1988). Results from investigating the hypothesis of Ker et al. (1988) was studied by the calculation of the mean and standard deviation from the area ratios of the 14 muscles. The mean was almost significantly different compared to the optimum of (34) calculated from the theory of Ker et al. (1988). This implies that the tendons experience stresses of about 11 MPa and strains of about 1-3%, when the muscles exert their maximum isometric forces. Very much larger forces would be needed to break the tendons. For each tendon sample, load versus displacement curves were plotted for the cyclic test with the highest maximal load. Experiment performed by Ker et al. (1988) consisted of measuring the area ratios for a majority of the limb muscles of different mammals. Stresses that would act in the tendons when the muscles exerted 0.3 Mpa was calculated by Ker at al. (1988). According to their findings, most of the stress was in the range of 5 Mpa and 25 Mpa with a manner in the laying at about 13 Mpa. The manner integer was noted to be close to the theoretical optimum. Stress of the calculations revealed that a small number of tendons exhibited more stress levels (Aagaard et al., 2001). A good example of such a tendon is the calcaneal tendon found in human beings; this tendon stress was estimated to be 67 Mpa. According to my mean results, I reject the hypothesis of Ker et al. (1988) based on the fact that my mean was higher than the optimum; this is evident from the p value obtained from the experiment being significantly higher than that deduced by Ker. I therefore reject this hypothesis. The hypothesis that consisted of the use of moment arm; isometric stress was analyzed and I concur with it. The multiple comparison table as well as ANOVA table helped prove the link of relative strengths of the muscles and muscle compartments examined as well as their actions. Muscle architecture, strength, fascicle length and optimum mass were evaluated. This second hypothesis has been presented by the use of graphs and statistical tables as well as density (p) values. Loss of muscle mass and function (sarcopenia) is one of the most marked problems associated with aging because it has major healthcare as well as socioeconomic implications. The mean free fat mass for this cadaver was 61.7 kg > or =2.0 standard deviations, P < 0.001. These observations suggest that sarcopenia is a progressive process, particularly in elderly men. Muscle strength comparison between muscle architecture and muscle action revealed that the isometric stress is constant. Thus this can be shown by the formula below: Moment arm in meters * PCSA *Isometric Stress (0.3mPA) = muscle strength The relationship between fascicle length and muscle compartment was examined by the use of ANOVA table analysis in proving whether this hypothesis is viable or not. There were differences among the means making the data statistically significant. As per the results, (p Read More