KINETICS IN OCCUPATIONAL THERAPY 1

Kinetics is a branch of classical mechanics that is focused on the movements of various bodies and the forces that can act on both bodies in motion and bodies at rest. Some people confuse the term with “kinematics,” because the two words sound similar, and they both have to do with the science of motion. In fact, “kinetics” itself is an out-dated term. Scientists prefer to say “analytical dynamics” or simply “dynamics.” The science of motion in the form of kinematics relies on some very clearly-defined laws, such as the concept that an object in motion tends to remain in motion. Kinetics expands upon these laws, adding some additional principles that help to explain what happens when external forces act on an object. This branch of classical mechanics recognizes the fact that many things can influence the outcome of a series of events, ranging from whether an object is dropped or hurled, to the obstacles the object encounters on its way to a destination. Many people are unconsciously aware of the laws of kinetics, because they use them on a daily basis, whether they are tossing a dirty fork into the sink from across the kitchen or designing bridges. Kinetics application is relevance in Occupational Therapy in various ways. It is basically apply to prevent injury and improve rehabilitation in terms of technique analysis and exercise given to the client. (Smith 2013)

One specific performance areas in occupation that I chose are leisure. Leisure is a non-obligatory activity that is intrinsically motivated and engaged in during discretionary time, that is, time not committed to obligatory occupations such as work, self-care, or sleep. (American Journal of Occupational Therapy, 2008). Example of leisure activities is playing basketball which involves jumping movement of human body. Jumping is acceleration of body parts upward to increase the mutual force between us and the earth above the force of body weight. Sir Isaac Newton penned three laws of motion that capture the essence of movement of bodies, human as well as inanimate. These laws have stood the test of time in our state of being close to the earth and travelling at modest speeds. One in particular, the third law, states that "action and reaction are equal and opposite." If you accelerate your arms upward, the muscular force required to do this has an equal and opposite reaction pushing the remainder of your body against the ground at your feet. The reaction to this force is that of the earth pushing up on you. When being try on your bathroom scales, you will see your weight apparently increase and decrease. The reason is that the bathroom scale is a force transducer that measures the ground reaction force. The subsequent apparent decrease in force is due to upward deceleration of the arms, which requires a downward force on the arms and an equal upward force on the remainder of the body. If our initial upward arm motion is sufficiently vigorous, the ground reaction force will go very high and subsequently drop to zero as we jump upward off our bathroom scale. This is jumping. We experience jumping as going upward because the earth is our reference for all things stable.

Kinetics knowledge can be applied in clinical practice for gait analysis of the patient. The integration of posture and movement utilizes anticipatory and reactive postural control mechanisms. The postural orientation of the individual relative to the base of support and gravity determines the movement strategies that will be accessible and effective. The alignment of body segments both at the initiation of movement and throughout the evolvement of movements plays a critical role in the postural control strategies utilized. The alignment of body segments in relation to each other and the base of support and the expression of postural control in relation to gravity and the environment are the key areas of focus in stroke rehabilitation and the treatment of other neurological conditions. (Graham et al. 2009)

One clinical case study for physical dysfunction is Pyia, who is a 75-year old woman who has treated for breast cancer 8 years earlier. She developed metastases, with an onset of acute, bilateral lower extremity weakness and loss of sensation. For 2 days she felt “unsteady” when she was walking and had one fall. By the time she was admitted to the hospital, she was unable to walk. After few weeks later, Pyia was asked to identify what areas of occupational performance were still problematic for her, what she could do well, and what her goals were. She replied that she was happy to be walking better but felt endurance was still a problem. She used the walker independently in the home but still needed assistance to get up and down stairs. (Heidi McHugh Pendleton and Winifred Schultz-Krohn. 2007) The kinetics application here can be explained by the third of Newton’s laws of motion which states that every applied force is accompanied by a reaction force. For every action, there is an equal and opposite reaction. During gait, every contact of foot with the floor or ground generates an upward reaction force. In the case of Pyia, she used walkers instead of her own foot due to the physical dysfunction. The upward reaction force is generated to the Pyia’s walkers while she walks instead of her foot.  The weight of Pyia is distributed over the walker so that she can also have good postural control while walking and maintain a stable gait with respect to the force from the ground.

One of biomechanics instrumentation for kinetics application is the use of dynamometer.  The client should be seated with the shoulder adducted and neutrally rotated, the elbow flexed at 90 degrees, forearm in neutral position, and wrist between 0 and 30 degrees extension between 0 and 15 degrees of ulnar deviation. It is important for the client to have an appropriate position while the therapist is taking the joint measurement of the patient. The force against gravity to the weight of the client can affect the reading of the grip strength of the dynamometer. Dynamometer is a device for measuring mechanical force, or power, transmitted by a rotating shaft. Since power is the product of torque (turning force) and angular speed, all power-measuring dynamometers are essentially torque-measuring devices; the shaft speed is measured separately. Among force-measuring devices are a flexible metallic ring that bends when a force is applied in such a manner as to tend to collapse it—the amount of bending being a measure of the applied force—and a hydraulic “load cell” that measures compressive loads in terms of fluid pressure. (Encyclopaedia Britannica 2013) A dynamometer has been designed for measuring isometric forces in human body limb segments.

Isokinetic contraction is the muscular contraction that accompanies constant velocity limb movements around a joint. The velocity of movement is maintained constant by a special dynamometer. The resistance of the dynamometer is equal to the muscular forces applied throughout the range of movement. This method allows the measurement of the muscular forces in dynamic conditions and provides optimal loading of the muscles . However, during movements in the vertical plane, the torque registered by the dynamometer is the resultant torque produced by the muscular and gravitational forces. The error depends on the angular position and the torque potential of the tested muscle group. Several methods have been developed for the correction of gravitational errors in isokinetic data. The torque output also contains artefacts that are associated with the inertial forces during acceleration and deceleration periods before the development of the constant pre-set angular velocity. For an accurate assessment of muscle function, only constant velocity data should be analysed.

The most frequently used isokinetic parameters are the maximum torque and the angular position where it was recorded, the torque output at different angular velocities of movement, the torque ratio of reciprocal muscle groups and the torque output during repeated contractions. The unique features of isokinetic dynamometry are optimal loading of the muscles in dynamic conditions and constant preselected velocity of movement. These features provide safety in the rehabilitation ofpatients with muscular and ligamentous injuries. Isokinetic dynamometry has also been used for the training of various muscle groups in order to improve the muscular performance in dynamic conditions. The movement velocity of different activities can be simulated during training in order to improve the training effect. Data acquisition and analysis have been improved by using computer systems interfaced to isokinetic dynamometers. Recently developed computer systems provide correction for gravitational and inertial errors, accurate computation of isokinetic parameters and real-time display of the torque output .

In a nut shell, knowledge of kinetics is important in Occupational Therapy practice. It is basically apply to prevent injury and improve rehabilitation in terms of technique analysis and exercise given to the client. Therapist observes the client’s movement and relates it to the ground or gravitational force with respect to the mass or weight of the client. Any postural impairments or physical dysfunction can affect the result of the client’s areas of occupation and performance areas respectively. The conditions face by the client should also being include in other to identify the best technique will be given to the client.

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