Isometric exercises are those in which muscular contraction occurs without a change in length of the muscle or joint position.
Isotonic strengthening or progressive resistance exercises are those in which the muscle contraction produces constant tension over a given range of motion.
Isokinetics are activities in which the speed of motion is constant and the resistance to motion adapts to the amount of force applied to the machine.
Closed kinetic chain
In closed kinetic chain exercises movement at one joint produces predictable movements at all other joints. Closed kinetic chain exercises allow co-contraction of agonist and antagonist muscles during functional movement which provides joint stabilisation by decreasing shear forces acting across the joint. It has been reported that dynamic co-activation of the quadriceps and hamstrings can reduce tibial translation by 200%, decrease internal and external rotation by 80% and enhance knee stiffness by 2 to 4 times. Weight bearing closed kinetic chain activities increase joint compressive force and thus enhance joint stability. In essence, a closed kinetic chain exercise is performed when the distal segment (foot) is relatively fixed such as a weight bearing exercise or a foot on the platform of a leg press machine or on the pedal of a bicycle.
Open kinetic chain
Open kinetic chain exercises use isolated joint and muscle function. Motion is uni-planer. Load is non-natural and sometimes abnormal. The foot is left free during open kinetic chain exercises such as resisted knee extension. A resisted force is applied to the distal tibia, tibial femoral sheer forces are maximised. Patello-femoral joint reaction stress is less during closed kinetic chain exercises than during open kinetic chain resistive exercises. Open kinetic chain exercises can be used for isolated training of quadriceps and hamstrings and does not therefore allow for co-contraction of agonist and antagonist muscles.
Concentric muscle contraction
A concentric muscle contraction occurs when the muscle body shortens as the contraction occurs. For example, when straightening the knee, the quadriceps contracts concentrically and shortens as the knee extends and straightens. This is a normal method of muscle contraction and strength training routinely used.
Eccentric muscle contraction
Eccentric muscle contraction occurs as the muscle body lengthens during the contraction. For example, if there is a weight attached to the ankle and the knee is slowly flexed (bent) under control, the quadriceps muscle contracts eccentrically and is lengthened during the activity. Eccentric strengthening programmes produce a much greater degree of strengthening per contraction and are a much more effective strengthening programme.
Isokinetic testing of the knee involves assessment of the quadriceps and hamstring muscle during a testing regime in which the speed is constant and the resistance is variable and accommodating.
Mechanical axis of lower limb
The mechanical axis of the leg is defined by a line running through the centre of the hip joint to the centre of the ankle joint. This line should pass essentially through the centre of the knee joint or just to the medial side of the centre of the knee joint. The distance of this line tangentially from the centre of the knee joint is referred to as the mechanical axis deviation. In a varus knee, the mechanical axis deviation passes through medial to the medial compartment of the knee and in a valgus knee the mechanical axis passes lateral to the middle of the knee.
The anatomical axis of a bone is represented by a line drawn down the centre of the medullary cavity of the bone. In the femur the mechanical and anatomical axes deviate whereas in the tibia the mechanical and anatomical axes are essentially represented by the same line. The angle between the long axis of the femur and the long axis of the tibia represents the anatomical axis angle which normally is 7° of valgus (figure 5.2, page 161 & figure 5.3, page 162 Insal)
A varus deformity of the knee is a bow-legged deformity. The deformity is defined in terms of the distal segment relative to the proximal segment. So, in the knee joint, a varus knee would mean that the distal segment represented by the foot has deviated medially (inwards towards the centre line of the body), relative to normal.
A valgus deformity of the knee is a knock-knee deformity. The distal segment represented by the foot has translated laterally, relative to normal.
In the anatomical position of the body, medial refers to structures closer to the mid line of the body. For example, standing with the feet pointing forwards, the medial compartment of the knee is the inner compartment, i.e. the compartment closest to the opposite knee (show picture).
In the anatomical position, lateral refers to a structure further away from the mid-line of the body. For example, standing with the feet pointing forward, the lateral compartment of the knee is the outer compartment, i.e. the compartment furthest away from the opposite knee (show picture).
Plyometrics is defined as a quick, powerful movement involving pre-stretching of the muscle and activating the stretch / shortening cycle could produce a subsequently stronger concentric contraction. Many movements pattern in sports and activities of daily living involve repeated stretch - shortening cycles. Plyometric training helps ensure that the knee being rehabilitated is prepared to accept the stress that will be placed on it during sports activities. Before plyometric exercises are incorporated into a treatment regime, range of motion and flexibility should be restored. Static and dynamic balance should be proved to be within acceptable ranges. The patient should also demonstrate a lack of apprehension in performing sports specific movements. An adequate strength base should also be developed. The patient should demonstrate the ability to descend and 8 inch step without pain and good lower extremity control (no deviation). Acceptable strength is demonstrated by the patient's power squatting 5 squat repetitions in 5 seconds with a weight equal to 60% of the patient's body weight.
Last Updated (Tuesday, 15 February 2011 09:39)
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