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The effects of an 8-week unilateral contract-relax (CR) stretching training program (passive stretch after isometric contraction) on muscular performance were investigated in a group of 16 athletes. The flexibility, maximum torque and angular position as well as contraction work in movements of the knee joint were determined before training and after 4 and 8 weeks of training. The torque measurements were performed under isokinetic conditions, eccentrically at angular velocities of 60 degrees x s(-1) and 120 degrees x s(-1), isometrically at five different joint positions, and concentrically at angular velocities of 60, 120, 180 and 240 degrees x s(-1) using an isokinetic dynamometer. A surface electromyogram (EMG) of the thigh muscles (quadriceps and hamstrings) was recorded simultaneously. As compared to untrained control limbs, significant improvements in active and passive flexibility (up to 6.3 degrees in range of motion), maximum torque (up to 21.6%) and work (up to 12.9%) were observed, and these were especially pronounced under eccentric load conditions. A comparison between integrated EMG recordings during eccentric and concentric loads, as well as the interpretation of the training-induced changes in the EMG, suggest that muscular activity under eccentric loads may be impaired by mental processes.

Based on the physiological principles of the muscular force-velocity concept, this paper deals with the special problems associated with determining and interpreting force-velocity relations of muscles in situ particularly in humans. In the strict sense, instead of force-velocity relations merely torque-angular velocity relations of a joint can be measured directly under in situ conditions. This calls for biomechanical model calculations to obtain force-velocity relations of single muscles involved in joint motions. In addition to discussing these basic principles, the methodological problems arising in measurements with so-called isokinetic dynamometers are also explicitly described. An important message of this paper is to sensitize potential users of this method to these problems as the isokinetic dynamometry has more or less become standard procedure worldwide. The possibility of the characterization of muscle fiber composition and the evaluation of power on the basis of human muscle force-velocity relations is also discussed. A final section considers the effects of muscle training on the torque-angular velocity relations. The contents of this paper can be understood as a guide to avoid obtaining conflicting results when measuring human torque-velocity relations.

Although it is generally accepted that ventricular geometric configuration plays an important role for manifestation of cardiac pumping failure, the relative significance of structural dilatation vs impaired myocardial performance- and the interaction of these factors-have not been thoroughly addressed. Besides its unfavorable effects on coronary circulation, cardiac energetics, and arrhythmogenesis, structural ventricular dilatation has direct consequences for stroke volume for geometrical reasons. As demonstrated by model calculations, the slope of the curve describing the relation between stroke volume and anatomical ventricular size is flattened and the maximum of the curve is shifted toward smaller end-diastolic volumes in the presence of reduced "contractility" or distensibility or after loss of contractile tissue. Further determinants of this curve are wall thickness and end-diastolic and systemic pressure. Based on the examples of human dilative cardiomyopathy and spontaneously hypertensive rats it can be shown that symptoms of pumping failure occur when the ventricular operating point has reached the maximum of the stroke volume-ventricular size relation or has even passed over the maximum, so that compensation via increase in ventricular size has been exhausted. However, neither ventricular dilatation nor severe myocardial impairment are a precondition for the occurrence of congestive symptoms if diastolic dysfunction is predominant or if hemodynamics and neuroendocrine reactions are substantially influenced by peripheral factors.

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