This figure shows superposed experimental records measuring the recovery time-course of the initial stiff phase of the tension response to movement. In this experiment, the myocardial preparation was subjected to two identical triangular length changes separated by an interval which ranged from 1 ms to 10 s in different trials. Individual trials were initiated at fixed intervals (in this case every 10 s) to ensure a constant recovery time.
Experiments of this type can be critically affected by series compliance in the connections between the muscle preparation and the motor/force transducer. Under these circumstances, a length change imposed by the motor is unevenly distributed along the muscle length and the ends of the muscle extend disproportionately, particularly at high levels of activation. As a result, the stiffness of the central core of the contracting fiber may be significantly underestimated.
SLControl allows the user to minimize this potential artefact by imposing the length change under sarcomere length control. In this mode, the motor is controlled by a feedback loop based on the measured sarcomere length of the preparation. Thus the motor moves sufficiently far to ensure that the sarcomere length in the contracting core of the fiber extends a fixed distance irrespective of the amount of series compliance.
SLControl can perform numerous different types of experiment under sarcomere length control including ktr measurements (the rate of tension recovery after a rapid length step), ramp and triangular stretches. In the latter cases, the velocity of the imposed stretch can also be varied at will.
Update rates of up to 2500 Hz can be maintained throughout the entire recording period, and the user can vary the gain of the feedback loop as required to match the system performance.