METHOD AND DEVICE FOR MEASURING OR DETERMINING AT LEAST ONE BIOMECHANICAL PARAMETER OF SOFT BIOLOGICAL TISSUES

Abstract

A method of measuring a biomechanical parameter of soft biological tissue is described. The method includes a pre-measurement process wherein an impulse applying device applies a pre-pressure to a surface of the tissue via an end portion contacting the tissue surface. While maintaining the pre-pressure, the device generates at least two impulses separated by a time interval, each impulse causing the end portion to impart to the tissue an action with certain parameters, each action inducing a response of the tissue. A value of a biomechanical parameter of the tissue is determined from each response induced. A determination is made as to whether the determined values of the biomechanical parameter are sufficiently similar to each other to indicate that the pre-pressure, the parameters of the end portion actions and the time interval are acceptable for use in a measurement process to be conducted on the surface of the tissue.

Claims

1. A method of noninvasively measuring a biomechanical parameter of soft biological tissue, using an impulse applying device comprising a movable testing body having an end portion to be placed in contact with a surface of the tissue, the method comprising a pre-measurement process which comprises: the impulse applying device applying a pre-pressure to the surface of the tissue via the end portion in contact with the surface of the tissue; whilst maintaining said pre-pressure, the impulse applying device generating at least two impulses separated by a time interval, each impulse causing the end portion to impart to the tissue an action with certain parameters, and each of the end portion actions inducing a response of the tissue; determining a value of a biomechanical parameter of the tissue from the response induced by each end portion action; and determining if the values of the biomechanical parameter determined from the response induced by each end portion action are sufficiently similar to each other to indicate that the pre-pressure, the parameters of the end portion actions and the time interval are acceptable for a measurement process to be conducted on the surface of the tissue using the same pre-pressure, a plurality of end portion actions with the same parameters and the same time interval.

2. A method as claimed in claim 1, wherein, if the determination is that the pre-pressure, the parameters of the end portion actions and the time interval are not acceptable for a measurement process to be conducted using the same pre-pressure, parameters of the end portion actions and time interval, the method further comprises a subsequent pre-measurement process which comprises: the impulse applying device applying to the surface of the tissue a subsequent pre-pressure, and whilst maintaining said subsequent pre-pressure, generating at least two subsequent impulses separated by a subsequent time interval each to cause the end portion to impart to the tissue a subsequent end portion action, at least one of the subsequent pre-pressure, the parameters of the at least two subsequent end portion actions and the time interval being modified; determining a value of the biomechanical parameter of the tissue from the response induced by each subsequent end portion action; and determining if the values of the biomechanical parameter determined from the response induced by each subsequent end portion action are sufficiently similar to each other to indicate that the subsequent pre-pressure, the parameters of the subsequent end portion actions and the subsequent time interval are acceptable for the measurement process to be conducted on the surface of the tissue using the same subsequent pre-pressure, a plurality of end portion actions with the same parameters as the subsequent end portion actions, and the same time interval as the subsequent time interval.

3. A method as claimed in claim 2, wherein the subsequent pre-pressure is modified compared to the pre-pressure used in the pre-measurement process carried out first.

4. A method as claimed in claim 2, wherein a parameter of the at least two subsequent end portion actions which is modified comprises a force per unit area applied by the end portion of the testing body to the tissue.

5. A method as claimed in claim 4, wherein the impulse applying device uses a second, different end portion to apply the at least two subsequent impulses, the second end portion having a different end area from that of the end area of the end portion used in the pre-measurement process carried out first.

6. A method as claimed in claim 2, wherein a parameter of the at least one subsequent end portion action which is modified comprises a duration of the end portion action.

7. A method as claimed in claim 2, wherein a parameter of the at least one subsequent end portion action which is modified comprises the time interval separating the at least two impulses.

8. A method as claimed in claim 1, wherein the biomechanical parameter of the tissue is its stiffness, and the pre-measurement process further comprises: for each of the end portion actions, determining a value of stiffness of the tissue to obtain a plurality of values of stiffness each corresponding to a respective end portion action; and said determining if the values of the biomechanical parameter determined from the response induced by each end portion action are sufficiently similar being done by performing a statistical analysis to determine a variation of the values of stiffness.

9. A method as claimed in claim 8, wherein the statistical analysis comprises: determining the mean of the values of stiffness; determining the standard deviation of the values of stiffness; selecting and discarding any of the plurality of values of stiffness that are greater than or less than the mean by more than a multiplier of the standard deviation; determining a new mean of the values of stiffness not discarded; determining a new standard deviation of the values of stiffness not discarded; wherein the variation determined by the statistical analysis comprises said new standard deviation.

10. A method as claimed in claim 9, further comprising: determining if all of the individual values of stiffness which are not discarded are inside an acceptable range, said acceptable range being +/− a multiplier of the new standard deviation from the new mean; and if all such individual values are inside the acceptable range, determining that the pre-pressure and the parameters of the impulse are acceptable for the measurement process to be conducted.

11. A method as claimed in claim 1, wherein the biomechanical parameter of the tissue is its stiffness and the stiffness S.sub.1is defined by the formula: $S_1=\frac{m_t*a_2}{\Delta l_1}$ where m.sub.t is the effective mass of the movable testing body, the effective mass being a mass value as if the whole of the movable testing body is being decelerated by a.sub.2, a.sub.2 is the maximum deceleration of the end portion, occurring when the tissue is maximally inwardly deformed by the at least one impulse, and Δl.sub.1 is the maximum inward deformation of the tissue caused by the at least one end portion action.

12. A method as claimed in claim 1, wherein the method comprises conducting said measurement process, said measurement process comprising: the impulse applying device applying a pre-pressure to the surface of the tissue via the end portion in contact with the surface of the tissue, the pre-pressure being the same as that used in the first or a subsequent pre-measurement process; and whilst maintaining said pre-pressure, the impulse applying device generating at least one impulse causing the end portion to impart to the tissue an action with certain parameters, the certain parameters being the same as those used in the first or a subsequent pre-measurement process, and the end portion action inducing a response in the form of natural oscillations of the tissue; and wherein the method further comprises: determining the biomechanical parameter of a first portion of the tissue extending from the surface of the tissue to a first depth, based on assessing data relating to the natural oscillations of the tissue during a first duration having a start time and a finish time; and determining the biomechanical parameter of a second portion of the tissue extending from the surface of the tissue to a second depth which is less than the first depth, based on assessing data relating to the natural oscillations of the tissue during a second duration having a start time and a finish time, the start time of the second duration being later than the start time of the first duration.

13. A method of determining at least one biomechanical parameter of soft biological tissue, the method using data obtained from a measurement process in which at least one action is applied to the surface of the tissue to cause natural oscillations of the tissue, the method comprising: determining the at least one biomechanical parameter of a first portion of the tissue extending from the surface of the tissue to a first depth, based on assessing data relating to the natural oscillations of the tissue during a first duration having a start time and a finish time; and determining the at least one biomechanical parameter of a second portion of the tissue extending from the surface of the tissue to a second depth which is less than the first depth, based on assessing data relating to the natural oscillations of the tissue during a second duration having a start time and a finish time, the start time of the second duration being later than the start time of the first duration.

14. A method as claimed in claim 12, wherein the start time of the second duration is at or later than the finish time of the first duration.

15. A method as claimed in claim 1, comprising using a camera provided on the impulse applying device to record a location on the tissue where the measurement of a biomechanical parameter thereof is being conducted.

16. A method as claimed in claim 15, comprising using a projector provided on the impulse applying device to project information about the location on the tissue where a previous measurement of a biomechanical parameter was conducted.

17. A method as claimed in claim 1, wherein the impulse applying device has a main body and an actuator for acting on the movable testing body, and wherein the actuator has a rotatable output member for applying torque to the movable testing body, the rotatable output member being non-rotatably connected to the movable testing body so that the movable testing body and the rotatable output member are rotatable about the same axis.

18. An impulse applying device for noninvasively measuring a biomechanical parameter of soft biological tissue, comprising: a main body; a testing body movably supported by the main body and having an end portion to be placed in contact with a surface of the tissue and to apply a pre-pressure to the tissue to cause inward deformation of the tissue in an inward direction, the pre-pressure being caused by the weight of the movable body when in a reference orientation relative to the direction of gravity; an actuator for acting on the movable testing body; and an accelerometer rigidly attached to the movable testing body for determining the orientation of the movable testing body relative to the direction of gravity, and if the orientation differs from the reference orientation, for outputting a signal which causes the actuator to act on the movable body to cause compensation for deviation of the movable testing body from the reference orientation, so that the pre-pressure is the same as that caused by the weight of the movable body when in the reference orientation, wherein the actuator has a rotatable output member for applying torque to the movable testing body, the rotatable output member being non-rotatably connected to the movable testing body so that the movable testing body and the rotatable output member are rotatable about the same axis.

19. An impulse applying device as claimed in claim 18, further comprising a plurality of interchangeable end portions each having a different test end area for contact with the surface, wherein said end portion of the testing body belongs to said plurality of interchangeable end portions, and can be removed and replaced by one of the other end portions of said plurality thereof.

20. An impulse applying device as claimed in claim 19, wherein each of the plurality of end portions has the same mass.

21. An impulse applying device as claimed in claim 20, comprising a further plurality of interchangeable end portions each having a different test end area for contact with the surface, wherein each of the further plurality of end portions has a second mass which is different from the mass of the first mentioned plurality of end portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0150] Certain preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which:

[0151] FIG. 1 is a schematic view of the impulse applying device;

[0152] FIG. 2 is a graph showing the natural oscillation curve of the soft biological tissue subjected to an action by an end portion of a movable testing body of an impulse applying device;

[0153] FIG. 3 is a graph showing stiffness values for 20 successive end portion actions spaced apart from each other by a time interval, for two different end portions; and

[0154] FIG. 4 is another graph showing stiffness values for 20 successive end portion actions spaced apart from each other by a time interval and using a different end portion.

DETAILED DESCRIPTION

[0155] The preferred embodiment of the impulse applying device to carry out real time measurement of the biomechanical parameters of soft biological tissue is shown schematically in FIG. 1.

[0156] The impulse applying device includes a casing with a handle 1, and data processing means in the form of a microprocessor and controller 2 used for directing the measurements, signal processing and calculating the biomechanical parameters.

[0157] A movable testing body 4 consists of a first arm portion 4a, a second arm portion 4b connected by a rotational joint to the first arm portion, and an end portion 4c connected by a bayonet connector 6 to the second arm portion 4b. The end portion has at its distal end a testing end 5 with a circular end area for contact with a measurement point of a region of tissue to be investigated. A sensor in the form of an accelerometer 3 is rigidly fixed to the first arm portion 4a of the movable testing body 4. The accelerometer is connected by wires 11 to the microprocessor and controller 2. The first arm portion 4a is rigidly fixed to a rotatable shaft of an actuator 7 supported on the casing 1, so that when the actuator is actuated and rotates by a certain amount (e.g. 1°) this in turn raises or lowers the first arm portion 4a of the movable testing body 4. The actuator is a rotary brushless torque actuator In this embodiment is a “Rotary BTA”, size 2 EVM as available from Ermec S.L.

[0158] A light emitting diode 8 is arranged on the casing 1 on one side of the first arm portion 4a, and a photodiode 9 is arranged on the casing on the opposite side of the first arm portion 4a. A shutter 10 is fixed to the first arm portion at the same radial distance from the rotational axis of the actuator as the light emitting diode 8 and the photodiode 9, so that when the first arm portion 4a rotates relative to the casing the shutter either interrupts light between the light emitter and the photodiode, or allows the light to pass from the light emitter to the photodiode.

[0159] The device further includes mechanisms for sound 12 and light signals 13 used for monitoring the measurement process; an arresting system of the testing end (not shown); a video camera 14 to record the investigated region and measurement locations to determine the point of measurement; a projector 15; a display 16; a battery 17; and a switch 18 to initiate the measurement.

[0160] If the axis of the end portion 4c does not coincide with the direction of the earth's gravitational field, the battery 17 current is used to actuate the actuator 7. The current is controlled by a signal from the accelerometer 3, according to the orientation of the first arm portion 4a of the movable testing body in the earth's gravitational field. By activating the actuator 7 with constant current, a torque applied to the first arm portion 4a of the testing body for, to urge the second arm portion 4b and the end portion 4c substantially linearly, so that the testing end 5 is in turn urged against the biological tissue to provide compressive force. This compensates for the axis of the end portion 4c not being in the vertical position, so that the pre-pressure of the testing end 5 on the tissue is the same as it would be if the end portion 4c work vertically orientated. In this way, the actuator can provide compensation for deviation of the end portion 4c from the vertical.

[0161] After the testing end is positioned on the point of measurement on the tissue, when lowering the device towards the point of measurement, the shutter 10, positioned on the first arm portion 4a of the movable testing body 4, obstructs the beam of light directed from the light emitter 8 towards the photodiode 9. This triggers the video camera 14 and the actuator 7 for a pre-defined duration, inducing, at the point of measurement, a change in the shape of soft biological tissue followed by a quick release (end of actuation). The soft biological tissue responds to the mechanical stimulus via natural oscillation that can be determined, for instance, by the accelerometer 3. This is achieved by the accelerometer determining the acceleration of the first arm portion 4a of the movable testing body 4, from which it is possible to determine the acceleration of the testing end 5. Since this is in contact with the surface of the tissue, the response of the tissue to the mechanical stimulus, in particular the acceleration of the surface of the tissue, can be determined.

[0162] The device is operated by a computer program product stored in the processor memory and including portions of the software code adapted to perform the method by stages when the program is running in the processor.

[0163] The device's construction and software (computer program) enable the user to achieve repeatability and reliability of the measuring results, allowing simultaneous measurement of the parameters and processing of data as well as making statistically significant judgements in real time.

[0164] Operation of an embodiment to carry out a method for noninvasively measuring in real time the biomechanical parameters of at least one layer of soft biological tissue includes the following steps.

[0165] Phase A—Set-Up/Pre-Measurement Process

[0166] (1) Selection of starting stimulation parameters (what seems reasonable for the patient/muscle concerned, for example the operator will start with a 3 mm diameter testing end and increase the diameter progressively if needed);

[0167] (2) The end portion of the movable testing body is put in contact with the skin (resting position) at the first pre-measurement point (anywhere in the area to be investigated);

[0168] (3) The device is lowered toward the pre-measurement point until it reaches its measurement position (the shutter obstructs the light passing between the light emitter and the photodiode);

[0169] (4) The microprocessor/controller is triggered (through the switch) and sends a signal to the actuator that generates a single short impulse that causes an action by the end portion on the tissue (stimulation of the soft biological tissue);

[0170] (5) Simultaneously, the microprocessor/controller activates the camera which takes a picture (measurement position is recorded);

[0171] (6) The acceleration sensor records the acceleration curve resulting from the co-oscillation of the movable testing body and the tissue, sends the information to the microprocessor/controller which calculates the stiffness of the soft biological tissue (any of the other biomechanical parameters could be used to determine their similarity but stiffness provides the best results)

[0172] (7) The device is raised to its resting position, so that the shutter no longer obstructs the light passing between the light emitter and the photodiode;

[0173] (8) Repetition of steps 1 to 7 as many times as necessary at time intervals (the number of repetitions can be programmed, but then it is needed to verify that enough data have been collected to perform a statistical analysis. An arithmetic mean is calculated, then the values that are >+/−2 SD are deleted and a new arithmetic mean based on the remaining values is calculated);

[0174] (9) If any of the non-deleted stiffness values >+/−0.5 SD, there is considered to be a residual strain with the parameters selected in (1), and so the stimulation parameters of the end portion actions are adjusted and steps (1) to (8) are repeated (in practice a testing end with a bigger diameter is selected and/or a shorter time of impulse is selected) in another pre-measurement point of the area (preferably at a point distant from the first one to avoid any effect of inadequate tissue recovery, i.e. residual strain) until all the non-deleted stiffness values <+/−0.5 SD which ends phase A.

[0175] Phase B—Measurements

[0176] (10) Selection of the stimulation parameters obtained in phase A (stimulation parameters that do not induce a residual strain, in the embodiment the selected end portion and duration of impulse);

[0177] (11) The end portion is put in contact (resting position) with the skin at the first measurement point (the data of the last pre-measurement point, without residual strain can be used as a first measurement point);

[0178] (12) The device is moved toward the measurement point until it reaches its measurement position (the shutter obstructs the light passing between the light emitter and the photodiode);

[0179] (13) The microprocessor/controller is triggered (through the switch) and sends a signal to the actuator that generates a single short impulse that causes an action by the end portion on the tissue (stimulation of the tissue);

[0180] (14) Simultaneously, the microprocessor/controller activates the camera which takes a picture (the measurement position is recorded);

[0181] (15) The accelerometer records the acceleration curve resulting from the co-oscillation of the movable testing body and the tissues, send the information to the microprocessor/controller which calculates the biomechanical parameters of the soft biological tissue of interest (i.e. preferably the skin and muscle) according to what is possible (depending on the number of periods of the acceleration curve, detailed below);

[0182] (16) The device returns to its resting position;

[0183] (17) Repetition of steps (11) to (16) as many times as necessary (the number of repetitions can be programmed, but then it is needed to verify that enough data to perform a statistical analysis have been collected. An arithmetic mean is calculated, then the values that are >+/−2 SD are deleted and a new arithmetic mean based on the remaining values is calculated. The new arithmetic mean is considered to be the stiffness value, i.e. the biomechanical parameter, which has been determined by the method);

[0184] (18) If the area requires more than one measurement point to be measured, as his preferred, the testing end of the device is put in contact (resting position) with the skin at a new measurement point of the area (following a logical scanning pattern, going from one point to the closest next one; since there is no residual strain, there is no need to go far, preferably the distance between 2 measurement points is calculated so that the circles of the end areas of the end portions of two consecutive positions are just touching (tangential)) and steps (12) to (17) are repeated;

[0185] (19) Step (18) is repeated as many times as necessary to cover the area of interest.

[0186] The accelerometer 3 obtains acceleration data about the part of the movable testing body on which it is mounted during and after an impulse is generated to cause an end portion action. From this the natural oscillation curve of the soft biological tissue is obtained. This is shown in FIG. 2. This figure shows three graphs showing (from the bottom) respectively acceleration, velocity and displacement. The displacement of the testing end 5 of the end portion 4c is shown as the “s” curve. Acceleration is measured by the accelerometer 3 and is shown by the “a” curve, this is integrated to obtain the velocity “v” curve, and this is further integrated to obtain the “s” curve. Further details are provided below.

[0187] FIG. 2 shows the natural oscillation curve of the soft biological tissue.

[0188] a—the acceleration graph of the joint oscillation of the testing end and the soft biological tissue;

[0189] v—a graph depicting the velocity of the testing end;

[0190] s—a graph depicting the displacement of the testing end and the biological tissue during joint oscillation;

[0191] t.sub.0—start of the active impact delivery by the actuator;

[0192] t.sub.1—the time of maximal velocity of soft biological tissue deformation;

[0193] t.sub.2—the beginning of the first period of natural oscillation, corresponding to the beginning of restoration of the shape of the soft biological tissue;

[0194] t.sub.3—the end of the restoration of the shape of the soft biological tissue in the first period of natural oscillation;

[0195] t.sub.4—the end of the overshoot Δs.sub.1 in the restoration of the shape of the soft biological tissue during the first period of natural oscillation;

[0196] t.sub.5—the beginning of the deformation in the first period of natural oscillation;

[0197] t.sub.6—the beginning of the second period of natural oscillation;

[0198] t.sub.7—the end of the restoration of the shape of the soft biological tissue in the second period of natural oscillation;

[0199] t.sub.8—the end of the overshoot in the restoration of the shape of the soft biological tissue in the second period of natural oscillation;

[0200] t.sub.9—the beginning of the deformation of the soft biological tissue in the second period of natural oscillation;

[0201] t.sub.10—the end of the second period of natural oscillation;

[0202] a.sub.1—the maximal acceleration during externally driven deformation of the soft biological tissue;

[0203] a.sub.2—the maximal deceleration during the deformation of the soft biological tissue induced by a single mechanical impulse;

[0204] a.sub.3—the acceleration at the time of maximal shape restoration overshoot of the soft biological tissue in the first period of natural oscillation;

[0205] a.sub.4—the deceleration at the end of the first period of natural oscillation of the soft biological tissue;

[0206] a.sub.5—the acceleration at the time of maximal shape restoration overshoot of the soft biological tissue in second period of natural oscillation;

[0207] a.sub.6—the deceleration at the end of the second period of natural oscillation of the soft biological tissue;

[0208] ΔS—static change in the shape of the soft biological tissue induced by pre-pressure;

[0209] Δl.sub.1—the dynamic change in the shape of the soft biological tissue induced by the actuator;

[0210] Δl.sub.2—the dynamic change in the shape of the soft biological tissue at the beginning of the second period of natural oscillation;

[0211] ΔS.sub.1—the overshoot in the restoration of the shape of the soft biological tissue in the first period of natural oscillation;

[0212] 66 S.sub.2—the overshoot in the restoration of the shape of the soft biological tissue in the second period of natural oscillation;

[0213] t.sub.1—First Natural Oscillation Period;

[0214] T.sub.2—Second Natural Oscillation Period.

[0215] Simultaneous but independent calculation of the biomechanical parameters for both superficial (cutaneous) and underlying deep tissues (including muscle) through the application of a single impulse may be carried out.

[0216] Combined superficial and deep tissue biomechanical parameters are calculated from the beginning of the acceleration curve until the end of the first natural oscillation period.

[0217] FIG. 3 shows a graph of values of stiffness of tissue measured at a particular measurement point using 20 impulses spaced apart at a time interval of one second, resulting in 20 end portion actions. The graph shows two experiments, one using a testing end having a circular end area with a 10 mm diameter (10 mm probe end in the graph) and the other using a testing end having a circular end area with a 12 mm diameter (12 mm probe end in the graph). All impulses were the same, but the force per unit area applied by the smaller testing end was greater than the force per unit area applied by the larger testing end. Thus, there was a greater energy density.

[0218] It will be seen that over the course of the 20 impulses for the 10 mm testing end there was an increasing trend in stiffness. This would indicate that no reliable assessment of biomechanical parameters can be made, because of the collection of residual deformation (or residual strain) over the course of the plurality of measurements. The graph additionally shows a straight line indicating the increasing stiffness.

[0219] In contrast, over the course of the 20 impulses for the 12 mm testing end, the stiffness values did not increase in size. There was some fluctuation of the values but overall they stayed about the same. This would indicate that a reliable assessment of biomechanical parameters can be made, because no residual deformation has been collected.

[0220] Thus, the result in FIG. 3 illustrates the accumulation of mechanical after-effects caused by a testing end having an end area which is too small.

[0221] FIG. 4 shows a graph of values of stiffness of tissue measured at a particular measure point using 20 impulses spaced apart at a time interval of one second, resulting in 20 end portion actions. Each impulse had a duration of 15 ms. This shows the stiffness values, a mean of those stiffness values and the +/−0.5 SD (standard deviation) range from that mean.

[0222] It will be seen that taps, or end portion actions, 1, 2, 3 or 4, exhibit a large increase in stiffness, caused by a duration of the actuator impulse which is too long, namely 15 ms.

DEFINITIONS

[0223] A biomechanical property is defined as a tissue's mechanical response to a mechanical impulse exerted on the tissue. By measuring the biomechanical properties of soft biological tissue, it is possible to foresee the danger of injury of a soft biological tissue. For instance, the breaking force (joint action of antagonistic muscles) resulting from repetitive trauma exerted on a soft biological tissue or the increase of muscle strain resulting from an increase in the rigidity of its collagen helicases may be detected by assessing the biomechanical parameters of these soft biological tissues, in particular the elasticity and creep. It will therefore be possible to treat the soft biological tissue before it is damaged.

[0224] Six Biomechanical Parameters of the Soft Biological Tissues

[0225] Of the biomechanical properties, stiffness characterizes the cooperative action of skeletal muscle antagonists during elementary motions (rotation of a body part around the axis of the joint) via the extent and character of the body part movement. As the stiffness of the collagen helices located in epimysium and skin increases, the body part movement amplitude decreases because the contraction of the skeletal muscle takes place during the transmission of mechanical energy due to the stiffening of the collagen helices located in the epimysium caused by rapid radial movement of myofilament cross bridges in the sarcomere (Vain, A. (2006). The phenomenon of mechanical stress transmission in skeletal muscles. Acta Academiae Olympiquae Estoniae, 14, 38-48).

[0226] The change in the stiffness properties of collagen in a skeletal muscle is the first signal of a functional disorder of the morphological structure of the soft biological tissue.

[0227] Stiffness is a biomechanical property of skeletal muscle which consists in its resistance to any force changing its shape. The property inversely proportional to stiffness is compliance. The unit of measurement of both is N/m. How economical and how accurately coordinated a person's movements are depends on the stiffness of his/her skeletal muscles.

[0228] The second biomechanical property is elasticity. A decrease in skeletal muscle elasticity leads to the risk of mechanical trauma of the perimysium. The underlying mechanism lies in the worsened blood supply (a decreased blood volumetric flow rate) since the post-contraction shape recovery is slowed down due to the slowly decreasing intramuscular pressure. Oxygen-deprived muscle signals about this with sensation of pain. Such a condition leads to atrophy of a skeletal muscle as an organ.

[0229] The logarithmic decrement of a muscle's natural oscillation shows how much mechanical energy dissipates during one period of the muscle's natural oscillation. Hence, the elasticity of skeletal muscle (one of the biomechanical qualities of the muscle) can be characterized via the logarithmic decrement of the muscle's natural oscillation. Elasticity of soft biological tissue means its ability to restore its former shape after the deforming force is removed. The opposite term to elasticity is plasticity. If an elastic body changes its shape as a result of an impulse transmitted by external forces, then simultaneously mechanical energy of elasticity is stored in the morphological structures of skeletal muscle which possess elasticity properties. When the impulse from the deforming force ends, then the stored mechanical energy will restore the body's initial shape at a velocity that accords to the value of the logarithmic decrement—very quickly if the value approaches zero, and more slowly if the value is higher. Hence, in a device built to register the parameter characterizing elasticity, the effect of oscillation damping must be brought to a minimum.

[0230] In a working muscle, contraction and relaxation alternate. The duration of each may vary. Sometimes it may last only a split of a second. If the relaxation period is short and the muscle's logarithmic decrement is big, then the initial shape of skeletal muscle fails to be completely restored, the muscle's internal pressure falls insufficiently and, as a result, the outflow of venous blood from the muscle is slowed down. The time taken for the muscle's work capacity to be restored increases, its fatigue also increases, and the danger of a muscle overload trauma becomes a reality.

[0231] Of the viscoelastic properties, creep characterizes the decrease in temporal rate of deformation of a biomaterial under stress. As a result, the increase in mechanical stress precedes the change in shape (deformation) and leads to biomaterial failure after exceeding the ultimate strength of the material. In case of a constant force impulse, the increase in the mechanical stress relaxation time leads to a decrease in the speed of motion.

[0232] Creepability is a biomechanical property of soft biological tissue to deform permanently under constant stress. The creepability property of liquids has been quantitatively measured (U.S. Pat. No. 4,534,211, Molina O. G. 1985).

[0233] The creepability property of soft biological tissue might be characterized, for example, by the Deborah number D.sub.e. The Deborah number is a quantity whose dimension is 1; this number is used to characterize the viscoelasticity of tissues (or creepability of materials). The latter is expressed as the ratio of relaxation time, t.sub.material representing the intrinsic properties of tissue, and the characteristic time scale of an experiment, or deformation time, t.sub.process:

[0234] Muscle tone—the existence of mechanical tension in resting state characterizes the state of biological tissue and affects the volumetric flow rate of intratissue microcapillary blood circulation in resting state (upon recuperation of performance of the skeletal muscle).

[0235] Tone is defined as the mechanical stress of skeletal muscle with no voluntary contraction of the muscle. If we multiply the numerical value of the skeletal muscle stress by its cross-section area, we get the value of the force by which the tendon of skeletal muscle is pulling the periosteum of the bone.

[0236] There are three types of tone:

[0237] 1) The passive resting tone—a state of skeletal muscle with no contraction in the muscle when the muscle is not balancing force torques on the observed joint axis caused by the force of gravity with its mechanical tension. There is no electromyographic (EMG) signal.

[0238] 2) The resting tone (relaxation)—a state of mechanical stress (or tension) of skeletal muscle without voluntary contraction with EMG activity due to, for instance, an emotional or pathological condition. Such a state is more variable than the passive resting tone. The muscle force torques in antagonist muscles are balanced.

[0239] 3) The postural tone is a state of skeletal muscle in which the muscle is balancing the force torques of body segments caused by the force of gravity in order to maintain the equilibrium position. When keeping the position, the muscle tension and stiffness are changing persistently, the variability of which is several times greater than in passive relaxed tone. The state of mechanical tension and stiffness level are also significantly higher.

[0240] The tone of the skeletal muscle cannot be decreased at will. The level of the tone depends on intramuscular pressure—the higher the intramuscular pressure, the greater the mechanical tensile stress in the muscle (Vain A. 2006 The Phenomenon of Mechanical Stress Transmission in Skeletal Muscles. Acta Academiae Olympiquae Estoniae, Vol 14, No. 1/2 pp. 38-48). If the intramuscular pressure is high, the outflow of venous blood from the muscle will slow down because the veins have no substantial internal blood pressure and when the intramuscular pressure rises, then the veins' cross-section area will decrease. In the case of passive rest, this causes the situation that skeletal muscles' ability to work is restored slowly. Additionally, the ergonomic efficiency of muscle activity in performing movements will decrease since the momentum of force caused by antagonist muscles for turning the part of the body on the axis of the joint increases on account of the work needed to stretch the antagonist muscles. The amount of work A done when stretching the antagonist muscles can be calculated by the following formula:

[0241] A=F.sub.resistance*S(J)

[0242] where F.sub.resistance—resistant force (N),

[0243] s—extent of stretch (m),

[0244] whereas F.sub.resistance=2*V*f*D*m(N),

[0245] where

[0246] v—speed of stretching (m/s),

[0247] f—muscle's natural oscillation frequency (Hz),

[0248] D—logarithmic decrement of a muscle's natural oscillation,

[0249] m—mass of the muscle being stretched (kg).

[0250] It is technically complicated to measure skeletal muscle's state of mechanical stress. However, there has been revealed a functional connection between a material's natural oscillation frequency and its mechanical stress, which in the case of short-term measurements makes it possible to characterize the mechanical state of skeletal muscle.

[0251] Coefficient of resilience characterizes the maximum energy that can be absorbed per unit volume without creating a permanent deformation (within the elastic limit).

[0252] Mechanical Stress Relaxation Time

[0253] The relaxation property of skeletal muscle tissue is defined as the tissue's ability to relieve itself of mechanical stress in the case of constant length.

[0254] When used independently, the biomechanical parameters of the soft biological tissues listed above do not provide a thorough understanding of the condition of the organ. Only when all the previously mentioned parameters are taken into account, the present state of the soft biological tissue can be assessed.

[0255] Other definitions (non-exhaustive list):

[0256] Real Time

[0257] In embodiments of the invention, the results of the pre-measurement process, any subsequent pre-measurement process and a measurement process can be obtained in real time. This is not the case in known impulse applying devices, where after the measurement it was necessary to plug the device into a computer to see any results. In this light, sampling frequency of 1 Hz and 30 kHz are both “real time”.

[0258] Soft Biological Tissues

[0259] All living tissues that exhibit natural oscillation upon subjecting it to a single mechanical impulse, for example: epithelial, subcutaneous, fatty, connective, muscle, nerve and cellular tissue.

[0260] List of tissues encompassed by the term “soft biological tissues”: muscles (different types), skin (epidermis +dermis), hypoderm (or subcutaneous tissue), tendons, ligaments, fascia, fat, fibrous tissues, connective tissues.

[0261] Layer (of Soft Biological Tissue)

[0262] The layers are defined by the self-oscillation periods, which also reflect on the mass of the tissue involved in the natural oscillation. This means that the “first” layer is the amount of tissue that mainly affects the parameters calculated from the first period of natural oscillation, which has the lowest oscillation frequency and has the highest amount of tissue mass involved. Subsequently next “layers” (or periods) have higher oscillation frequencies and less mass is involved, up to the last layers/periods, where only skin is involved.

[0263] For example, in the case of an acceleration curve that has 14 peaks, a first layer is calculated from maxima t6−t2, a second layer is t10−t6 and a third (and last) layer is t14−t10.

[0264] The layers are theoretical, not physical layers, but still approximately correlate to the actual physical layers: first periods of natural oscillation (first layers) characterize mainly the muscle and last periods (last layers) characterize mainly skin.

[0265] The Acceleration Curve

[0266] The acceleration curve is a curve showing the acceleration of the testing end during the pre-measurement process or measurement process (“measurement”). Since the testing end is in contact with the soft biological tissue, the curve depicts the total acceleration of the testing end + the tissue it is in contact with.

[0267] Natural Oscillation (Period, Frequency)

[0268] Oscillation induced by a single external impulse

[0269] This can be seen as the portion on the acceleration curve/graph that begins immediately after the end of actuation (mechanical impulse), starting at t2 in FIG. 2.

[0270] Longitudinal Measurement

[0271] Measurement where the measuring device is removed from the measuring area (area of tissue) and the measurement is repeated later on the same area. This is in contrast with doing subsequent measurements on the same area without removing the device. For example, if an area is measured during 1 minute and the device is removed for 1 minute and then the device is used to measure again on the same area for 1 minute (total of 3 minutes), this is a longitudinal measurement. If the same area is measured during the course of 10 minutes without removing the measurement device from the area—this is not a longitudinal measurement.

[0272] Formulas for calculation of the biomechanical parameters of soft biological tissue are provided in TABLE 1.

[0273] i=1, 2, 3, etc.—sequential number of the natural oscillation period (T.sub.1, T.sub.2 in the FIG. 2) suitable for calculations.

k=i−1

[00002]$6_i=\frac{a_{2i}{m}_t}{L},$

where mt is the mass of the movable testing body and L is the area of the testing end [m.sup.2] and

[00003]${\mathrm{.Math.}}_i=\frac{\Delta l_i}{\Delta S_i+\Delta l_i}$

TABLE-US-00001 TABLE 1 Parameter Generalized formula I period II period III period Natural oscillation frequency [Hz] [00004]$F_i=\frac{1}{t_{4i+2}-t_{4i-2}}$ [00005]$F_1=\frac{1}{t_6-t_2}$ [00006]$F_2=\frac{1}{t_{10}-t_6}$ [00007]$F_3=\frac{1}{t_{14}-t_{10}}$ Dynamic stiffness [N/m] [00008]$S_i=\frac{m_t*a_{2i}}{\Delta l_i}$ [00009]$S_1=\frac{m_t*a_2}{\Delta l_1}$ [00010]$S_2=\frac{m_t*a_4}{\Delta l_2}$ [00011]$S_3=\frac{m_t*a_6}{\Delta l_3}$ Logarithmic decrement [00012]${\Theta }_i=\ln \left(\frac{a_{2k+2}}{a_{2k+4}}\right)$ [00013]${\Theta }_1=\ln \left(\frac{a_2}{a_4}\right)$ [00014]${\Theta }_2=\ln \left(\frac{a_4}{a_6}\right)$ [00015]${\Theta }_3=\ln \left(\frac{a_6}{a_8}\right)$ Mechanical R.sub.1 = t.sub.4i−1 − t.sub.4i−2 R.sub.1 = t.sub.3 − t.sub.2 R.sub.2 = t.sub.7 − t.sub.6 R.sub.3 = t.sub.11 − t.sub.10 stress relaxation time [ms] Deborah number [00016]$C_i=\{\begin{array}{cc}{R}_i\text{/}\left(t_{2i}-t_0\right)& i=1\\ R_i\text{/}\left(t_{4i-2}-t_{4i-3}\right),& i\ne 1\end{array}$ [00017]$C_1=\frac{R_1}{t_2-t_0}$ [00018]$C_2=\frac{R_2}{t_6-t_5}$ [00019]$C_3=\frac{R_3}{t_{10}-t_9}$ Coefficient of resilience [J/m{circumflex over ( )}3] [00020]${\mathrm{Re}}_i=\frac{6_i{\mathrm{.Math.}}_i}{2}$ [00021]${\mathrm{Re}}_1=\frac{6_1{\mathrm{.Math.}}_1}{2}$ [00022]${\mathrm{Re}}_2=\frac{6_2{\mathrm{.Math.}}_2}{2}$ [00023]${\mathrm{Re}}_3=\frac{6_3{\mathrm{.Math.}}_3}{2}$

[0274] Calculation of Biomechanical Parameters of Different Portions of Soft Biological Tissues

[0275] The oscillation curve can be divided in distinct portions (based on the curve of FIG. 2): the mechanical impulse (from t.sub.0 to t.sub.2) and subsequent natural oscillation periods: first period T.sub.1 (from t.sub.2 to t.sub.6, corresponding to a.sub.2 to a.sub.4), second period T.sub.2 (from t.sub.6 to t.sub.10, corresponding to a.sub.4 to a.sub.6), etc.

[0276] The portion of acceleration curve that is used in the calculations is from the beginning of the curve (t.sub.0) up to the peak a.sub.n, as long as [0277] a.sub.n>a.sub.2*σ.sub.s, where [0278] a.sub.n—the sequential local maxima/minima, counting from the beginning of the acceleration curve, n=1, 2, 3, etc.; and [0279] a.sub.2—the maximal deceleration during the first natural oscillation period of the soft biological tissue.

[0280] 1) If no natural oscillation period is recorded—the stiffness of only the superficial tissue (the skin) is calculated, using the second half-period (a.sub.1-a.sub.2) of the active (external) deformation period (t.sub.0-t.sub.2 on FIG. 5).

[0281] 2) If at least a quarter of the first natural oscillation period is obtained, then according to how much of a given natural oscillation is obtained, for every natural oscillation period T.sub.i, can be calculated: [0282] a. The stiffness of the portion of biological tissue that contributes to the natural oscillations in period T.sub.i based on the second half-period of the previous oscillation period T.sub.i-1. [0283] b. The Mechanical stress relaxation time, and the Deborah number (which characterizes creep) of the muscle based on the first quarter of the period T.sub.i. [0284] c. The coefficient of resilience, based on the first half of the period Ti; [0285] d. The logarithmic decrement and the natural oscillation frequency, based on the whole period T.sub.i.

[0286] Presented differently, for a given period Ti, it is possible to:

[0287] 1) Use the second half-period of the previous oscillation period (which is a natural oscillation in cases of T.sub.2, T.sub.3 . . . T.sub.i, or the external mechanical deformation period t.sub.0-t.sub.2 in the case of T.sub.1) to calculate the stiffness of the tissue involved in natural oscillation in period T.sub.i(i=1, 2, 3 . . . ).

[0288] 2) Use the first quarter of the period to additionally calculate mechanical stress relaxation time, and Deborah number of the tissue involved in natural oscillation in period T.sub.i.

[0289] 3) Use the first half of the period T.sub.i to calculate the coefficient of resilience for the tissue involved in natural oscillation in period T.sub.i.

[0290] 4) Use the full period Ti to additionally calculate the logarithmic decrement and the natural oscillation frequency for the tissue involved in natural oscillation in period T.sub.i.