Answer
The skeletal muscles increase stroke volume by increasing preload end diastolic volume.
Work Step by Step
Three of the main factors that influence the size of ventricular stroke volume are preload, contractility of ventricular myocardium, and afterload. The contraction of skeletal muscles influences preload. This effect is mediated through the enhancement of the return of blood to the heart which increases stretch of ventricular myocardium. As a consequence, the ventricular end systolic volume increases. According to the Frank-Starling's law of the heart, increased stretch of the myocardial fibers results increased force of contraction(snap back). So the increased preload causes increase of ventricular end diastolic volume as well as increased force of contraction of ventricular myocardium at ventricular systole. The ultimate result of this increase in preload is increased ventricular stroke volume
