THE BIOMECHANICAL MODEL

                        THE BIOMECHANICAL MODEL

1.      FOCUS:

·          Musculoskeletal capacities that underlie functional motion in everyday occupational performance 

·         How the body is designed and used to accomplish motion for occupational performance 

·         Applied to persons who experience limitations in moving freely, with adequate strength, and/or in a sustained fashion

·         Based on these biomechanical and physiological principles, occupational therapists can design treatment programs to address ROM, strength, and endurance problems affecting occupation.

2.      THEORY:

·         Kinetic and kinematic principles concerning nature of movement and forces acting on the human body as it moves  Anatomy of musculoskeletal system  Physiology of bone, connective tissue, and muscle and cardiopulmonary function

·          Capacity for functional motion is based on:

ü  Potential for motion at the joints (joint range of motion)

ü  Muscle strength (ability of muscles to produce tension to maintain postural control and move body parts)

ü  Endurance (ability to sustain effort [i.e., intensity or rate] over time required to do a particular task) 

·         Joint range of motion depends on structure and function of joint and integrity of surrounding tissue, muscle, and skin

·          Muscles cross one or more joints and exert force to control or produce movements allowed by the structure of the joints

·          Performance depends on simultaneous action of muscles across many joints producing stability and movement required for a task

·          The ability to sustain muscle activity (i.e., endurance) is a function of muscle physiology in relationship to work being done and supply of oxygen and energy materials from cardiopulmonary system 

·         Movements produced during occupational performance are as much a function of dynamic circumstances of performance

·         Capacity for movement (i.e., strength, range of motion, and endurance) affects and is affected by occupational performance

3.      AIM AND OBJECTIVES:

·         Prevent deterioration and maintain existing movement for occupational performance

·         Restore movement for occupational performance if possible

·         Compensate \adapt for loss of movement in occupational performance

4.      BASIC ASSUMPTIONS:

·         Successful human motor activity is based on physical mobility and strength

·         Participation in activity involving repeated specific graded movements maintains and improves function

·         Activity can be graded progressively to meet particular demands within an intervention programme

5.      THEORETICAL BASE ASSUMPTIONS:

·         The belifes that the purposeful activities can be used to treat loss of ROM, Strength and endurance

·         The belief that after ROM, strength and  endurance regained, the patient automatically regains function

·         The principle of rest and stress. First the body must rest to heel itself. Then the peripheral structure must be stressed to regain range ,strength and endurance

·         The belief that the biomechanical frame of reference is best suited for patients with an intact CNS. Patient may have limited range strength, endurance but have the ability to perform smooth, isolated movements         

6.      PROBLEMS AND CHALLENGES:

·         Problems exist when a restriction of joint motion, strength, and/or endurance interferes with everyday occupations

·          Joint range of motion may be limited by joint damage, edema, pain, skin tightness, muscle spasticity (excess muscle tone producing tightness), or muscle and tendon shortening (due to immobilization)

·          Muscle weakness can occur as a result of:

ü  Disuse

ü  Disease affecting muscle physiology (e.g., muscular dystrophy) •

ü  Diseases and trauma of lower motor neurons (e.g., polio), spinal cord, or peripheral nerves, which can result in de-innervation of muscles

·         Endurance can be reduced by:

ü  Extended confinement or limitation of activity

ü  Pathology of cardiovascular or respiratory systems

ü  Muscular diseases

·          It is common for sensory loss and loss of motion to co-occur because tactile sensations or touch are often affected by the same diseases or traumas that affect muscles 

·         Pain can be chronically or periodically present in association with disease or trauma that affects the musculoskeletal system

7.      BIOMECHANICAL INTERVENTION:

·         Interventions focus on intersection of motion and occupational performance and can be divided into three approaches:

ü  Prevention of contracture and maintenance of existing capacity for motion  

ü  Restoration by improving diminished capacity for motion

ü  Compensation for limited motion (sometimes referred to as a rehabilitation approach)

·          Intervention aims to minimize any gap between existing capacity for movement and functional requirements of ordinary occupational tasks

8.      PRACTICE RESOURCES :

·          Range of motion is usually measured with a goniometer calibrated to degrees of movement about an axis 

·         Strength is normally tested by manual muscle testing in which the therapist (alone or using some instrument) tests the ability of a person to produce resistance and/or movement under standardized circumstances

·          Endurance is usually measured by determining duration or number of repetitions before fatigue occurs  Methods of intervention address not only targeted limitations of motion, strength, and endurance, but also their underlying causes because the latter may determine the most appropriate intervention.

·         Measuring endurance, three factors are ordinarily considered: intensity, duration, and frequency. 

·         Strength is developed by increasing stress on a muscle through:

ü  Amount of resistance offered to the movement

ü   Duration of resistance required

ü   Rate (speed of movement) of an exercise session

ü  Frequency of sessions  Occupations

ü  Provide natural and motivating circumstances for maintaining musculoskeletal functioning

ü   Employ attention, thereby encouraging greater effort, diminishing fatigue, and diverting attention from pain or fear of movement

ü  Provide conditioning that more nearly replicates normal demands for movement in everyday life

·          Attention to functional purpose of a task is important because purpose does appear to exert an organizing influence on movement

·          Activity may be modified to:

ü  Reduce or alter task demands and prevent musculoskeletal problems • Match permanently reduced musculoskeletal capacity

ü   Intensify task demands that will increase musculoskeletal capacity

·         Ways to modify an activity include:

ü  Positioning the task

ü  Adding weights or other devices that provide assistance or resistance to movements performed in the activity

ü   Modifying tools to reduce or increase demands

ü   Changing materials or size of objects used

ü   Changing method(s) of accomplishing task

·          When using adapted activities it is important that the client be involved in occupational performance that does have some meaning and relevance

·          When persons do not have biomechanical capacity to perform daily living, leisure, and work tasks in ordinary ways, special equipment and modified procedures can compensate (i.e., close the gap between a person’s capacities and task demands) 

·         Prescription, design, fabrication, checkout, and training in use of orthoses may be employed to support, immobilize, or position a joint to prevent/correct contractures and/or enhance function Current approaches (such as work hardening) emphasize strengthening by having the client perform tasks required by that person’s occupation

9.      PRINCIPLES:

9.1.Positioning

·         When a person’s limb is too weak to resist gravity, positioning in a resting or functional position is essential to avoid development of deformities, minimize edema, and maintain ROM gained in treatment.

·         Positions of function are encouraged, and all non-functional positions are avoided throughout the day and night.

·         In particular, positions that are opposite of normal patterns of tightness should be encouraged for at least periods of the day.

9.2.Compression

·         Compression is used to prevent ROM limitations secondary to edema.

·         Edema can be controlled by compression with elastic strip or tubular bandages.

·         The occupational therapist must take care to apply these correctly so they do not constrict circulation in the more distal part of the extremity. Skin color is observed regularly to confirm that circulation is preserved.

·         Compression is most effective in eliminating edema when combined with positioning and passive or active movement of the limb.

9.3.The methods used for movement through full ROM

·         Teaching the patient to move the joints that are injured, immobilized, or edematous  

·         Passively moving the joints if the patient cannot.

·         The ranging technique for active ROM (AROM) and passive ROM (PROM) are similar.

·         In AROM, the patient actively performs the desired motion. In PROM, the therapist gently moves the patient’s limb through the desired motion, paying particular attention to planes of motion and joint biomechanics

·         PROM can also be performed by external devices, such continuous passive motion (CPM) machines.

·         AROM is preferred to PROM for reduction of edema because the contraction of the muscles helps pump the fluid out of the extremity. If AROM is not possible, however, PROM can aid in reducing edema. Positioning of the edematous extremity above the heart during distal PROM is recommended to aid in venous return.

·         Occupational therapists often structure activities to provide AROM to prevent limitations in ROM.

9.4.Stretching

·         Stretch is a process by which tissue is lengthened by an external force, usually to eliminate tightness that has the potential to cause a contracture.

·         Defined as a few degrees beyond the point of discomfort, and held there for between 15 and 30 seconds (Bandy & Sanders, 2001). The force, speed, direction, and extent of stretch must be controlled (Kisner & Colby, 2002; Salter & Cheshire, 2000).

·         The stretch is applied to the point of maximal stretch. Gentle stretching that achieves small increments of gain over time is more effective than vigorous stretching aimed at large, rapid gains.

·         A study of healthy subjects found that 30 seconds of passive stretch was as effective as 120 seconds (Ford, Mazzone, & Taylor, 2005).

1.      Active Stretching

ü   The goal of increasing ROM.

2.      Passive Stretching

ü  passive stretching prior to engagement in occupation

9.5. Increase stress of muscle

·         Isometric

·         Isotonic

·         Concentric

·         Eccentric

9.6.Strengthening

·         Occupation or exercise parameters that may be manipulated to increase stress to a muscle include type of contraction, intensity or load, duration of contraction, rate or velocity of contraction, and the frequency of exercise.

·         It is important to realize that strengthening is a very specific process, that muscle will only gain strength within the range of motion that is exercised, and that the speed of contraction is quite specific.

·         Therefore, if there are specific activities that the strengthening is being designed to address, the types of contractions, ranges of motion, and speed of contraction of the strengthening program should be similar to the performance environment.

·         If the patient needs general strengthening, then the types of contractions, ranges of motion, and strength of contraction should be varied

·         Guidelines for a Strengthening Program

Isometric

ü  Exercises in which a  weak muscle is isometrically contracted to its maximal force 10 times with rest periods between each contraction

ü  Trace{0}The force of contraction is not sufficient to move the part.

ü  Provide a stimulating environment.

ü  Explain procedures. Instruct the patient to contract the weak muscle (“hold”).

ü  External resistance applied by the therapist may help the patient isolate the contraction to the weak muscle or muscle group.

ü  Patient holds contraction at maximum effort as long as possible while breathing normally.

ü  Repeat 10 times with a rest between each contraction. Increase duration of maximal contraction as patient improves.

ü  Maximal isometric contraction is contraindicated for patients with cardiac disease

                                  Isotonic Assistive (Active Assistive ROM)

ü  Exercise in which a weak muscle is concentrically or eccentrically contracted through as much ROM as patient can achieve; therapist and/or external device provides assistance to complete motion

ü  Poor minus {2-} Fair minus {3-} The muscle can move only through partial available range in either a gravity-eliminated or against-gravity plane.

ü  Provide a stimulating environment. Explain procedures. For a 2- muscle, position limb to move in a gravity-eliminated plane. For a 3- muscle, position the limb to move against gravity. Patient moves weak muscle through as much range as possible. Therapist provides external force to complete motion. Although this seems similar to PROM, it differs because patient actively attempts to contract weak muscle

                            Isotonic Active (Active ROM)

ü  Patient contracts muscle to move part through full ROM.

ü  Poor (2) Fair (3) Muscle can move through full available range in either gravityeliminated or against-gravity plane.

ü  Provide a stimulating environment. Explain procedures. For a 2 muscle, position the limb to move in a gravity-eliminated plane. For a 3 muscle, position the limb to move against gravity. Patient moves weak muscle through full available ROM. Patient repeats motion for 3 sets of 10 repetitions with rest break between sets.

                       Isotonic Active Resistive (Active Resistive ROM)

ü  Patients contracts muscle to move part through full available ROM against resistance.

ü  Poor plus (2+) Fair (3) Fair plus (3+) Good (4) Good plus (4+)

ü  Provide a stimulating environment.

ü  Explain procedures. For a 2+ or 3 muscle, position limb to move in gravity-eliminated plane. For a 3+ or above muscle, position limb to move against gravity.

ü  Therapist determines appropriate amount of resistance depending on the strengthening protocol chosen. If the DeLorme protocol is used, the 10-RM is established, which is the maximum weight a patient can lift through 10 repetitions with smooth controlled movement. If the simplified protocol is used, the 1-RM is established, which is the maximal amount of weight the patient can lift one time in a smooth controlled movement.

ü  Patient moves weak muscle through full available ROM against resistance.a If the DeLorme protocol is used, the patient does 3 sets of 10 repetitions with varying resistance and rest break between sets. If the simplified protocol is used, the patient does 4 sets of 10 repetitions at a set weight with rest breaks between sets.

10.  FUNCTION-DYSFUNCTION:

·         Structural stability

·         Range of motion

·         Edema

·         Strength

·         Low level endurance

·         High level endurance

11.  METHODS OF TREATMENT:

·         Manual streaching

·         Joint mobilization

·         Joint exercises and activities

·         Isotonic active exercises

·         Isometric exercises {progressive prolonged isometric tension method\ progressive weighted  isometric elangation method }

·         Progressive resistive exercise

·         Regressive resistive  exercises

12.  MERITS:

·         The biomechanical frame of reference makes good use of media and equipment to promote physical  functions

·         It can be applied to  a variety of creative and constructed activities

·         It use knowledge of activity analysis to good effect

·         It utilizes the increased knowledge of anatomical, physiological and kinaesthetic processes in humans

·         It has led to the development of specific techniques for measuring movement strength and endurance

13.  LIMITATION:

·         The biomechanical frame of reference focuses on physical performance in the absence of volition ,role duties or environmental influences it is specifically based in physical activity with no reference to motivation  or the psychological ,emotional or social aspects of rehabilitation

·         It does not address the need for balance in activity in daily life .it emphasizes lower levels for survival –mobility and physical function-but does not follow through to the higher levels of self-esteem and self -actualization

·         It is not applicable to people whose central nervous system is impaired. The emphasis is on the promotion of physical mobility. Therefore this frame f reference has limited