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日期：2020-09-29 07:16

Functional Muscle Architecture of the Human Upper and Lower Limb

You are each encouraged to read around the subject area to generate a clearer understanding of the topic. This will prepare you for the data analysis and interpretation.

Background

Knowledge of the architecture of a muscle, together with its relationship to the skeleton and joints provides powerful insight into the possible roles and importance of a muscle (or muscles) in, for example, the production of a particular joint movement or generation of force to stabilise a joint.

Quantitative analysis of muscles in the upper and lower limbs in multiple cadavers has, over previous years, produced a large dataset which can be interrogated in relation to questions about muscle-tendon interactions, and more generally about the function of different muscles or compartments.

Primary Aims

1.To analyse, graph and interpret data to test the hypothesis of Ker et al., (1988) that ‘muscle‐tendon units are optimised for minimum combined mass’.

2.To calculate the relative strengths of individual muscles, and the combination of muscles in compartments and discuss these in relation to their associated actions.

The Methodological Approach used to generate the data

?Muscles are identified, and sites of origin and insertion determined.

?An in situ determination of the tendon’s moment arm about the wrist joint (upper limb dissection) or the ankle and sub-talar joint (lower limb dissection) is made.  

?A segment of tendon of known length (this should be as long as possible to reduce weighing error) is weighed – this mass and the associated length of the specimen will permit the tendon’s cross-sectional area to be calculated using a standard value for tendon density of 1139 kg m-3  – see Spreadsheet provided on the website.

?Each muscle belly is dissected-free of the limb and any remaining external tendon of insertion (and origin) removed.  

?The mass, without external tendon, is measured.

?An incision is made, parallel to the surface aponeurosis, and the belly is opened to allow the internal structure to be viewed for the determination of fascicle (fibre) length and the angle the fibres make relative to the tendon of insertion (= line of action of the muscle tendon unit).  

?Small groups of fibres are carefully dissected-free and mounted on a microscope slide in glycerol jelly and a coverslip used to create a temporary mount – for subsequent determination of sarcomere spacing.

Data Analysis

Each student will produce an individual analysis and presentation of their results, as might appear in the results section of a manuscript for publication. As students, you have access to various graphing and statistical packages (e.g. SigmaPlot, Graphpad Prism).  You will each have 8 Lower limb and 8 Upper limb datasets to work with.

Marks for each section shown below.

Aims/approaches:

?To Provide a brief explanation of the hypothesis that suggests that the area ratio of physiological cross-sectional area (CSA) of a muscle to the CSA of its attached tendon is 34 : 1  and to conduct appropriate statistical analyses to test whether your data support or challenge the working hypothesis that the area ratio (PCSA : CSAtendon) = 34 : 1.  This should be done: (a) muscle by muscle (e.g. Fl carpi ulnaris (n = 8 muscles, one each from the 8 subjects), Ext carpi ulnaris (n = 8), etc.) and; (b) by analysing all of the muscles together (n = 182 (or thereabouts) to give an overview.  

Provide a brief interpretation of the results (Max. 120 words: 4 marks)

?Produce frequency plots for calculated tendon stresses.  You have some flexibility here, but I suggest presenting UL and LL tendon stresses on separate graphs.  You may wish to highlight certain tendons (e.g. Achilles tendon results, hint).  Provide brief interpretation of the important points that the data show (max. 100 words: 3 marks).

?Explain why normalisation of data is important when comparing measures collected from a random sample of a population, and calculate a mean normalised maximum isometric force that could be generated in life by each of the muscles for which you have data.  Graph these data.  Explore the data statistically to see which muscles differ significantly from others (Max. 120 words: 4 marks).

?Calculate the mean normalised torque for (a) flexion, extension, ulna deviation and radial deviation for the upper limb, and (b) dorsiflexion, plantarflexion, inversion and eversion for the lower limb. Are the antagonistic torques of a significantly different magnitude? If so, why? (100 words max.: 4 marks)

?Explain in terms that would be suitable for a person without a scientific background why the hypothesis about minimisation of mass of tendon-muscle units is not expected to apply to those units that can usefully store elastic strain energy during locomotion (Max. 100 words; 1 mark).

Available files

The excel file"Example of normalised spreadsheet" is uploaded here, along with a spreadsheet that provides the summed mass of all muscles in the respective spreadsheets - and shows how normalisation can be applied.

The file "Example of normalisation" gives a worked example of the effect of normalisation on two muscles.  Note: in this example the moment arms values differ among individuals...I have eliminated this source of variation (unreliability?) in your datasheets, as all individuals are now allocated the same moment arm value for each muscle's function, e.g. FCU has a moment arm of 20 mm for ulnar deviation, and 16 mm for wrist flexion.