Concentric Contraction Muscle at Rest Myosin Z line
Actin Muscle Contraction Myosin
Actin
Figure 3.5 The biceps is performing a concentric contraction representing the actin and myosin filaments sliding toward each other.
Clinical Connection 3.1
Isokinetic exercise and testing consists of dynamic muscle work based on the principle that the rate of the body segment moving through the range of motion is maintained at a constant speed. Typically, the exer- cise and testing are done on an isokinetic dynamom- eter such as the Biodex, Cybex, or Kin-Com. The machine adjusts its output resistance to movement in response to the torque force produced by the muscle to maintain the body segment at constant speed. If the muscle force increases, the resistance provided by the machine increases so that the limb main- tains the preset constant speed throughout the arc of movement.
During testing, the dynamometer measures the maximal torques produced by muscles at various speeds. The clinician can compare these measure- ments with torques produced by the contralateral uninvolved muscles. Isokinetic equipment is also used for strength training at various speeds of movement. Research studies frequently use isokinetic testing to measure patients’ progress in rehabilitation. Wong and colleagues showed that patients who underwent an anterior cruciate ligament repair of the knee con- tinued to demonstrate functional hip and isokinetic knee extension defi cits compared with the uninvolved limb at 6 to 9 months after surgery.
