io6 



PHYSIOLOGigAL TRIGGERS 



FIG. lA 



-R -Xc -R 



Fig. I. A, force vector diagram of the model vibrating system. OA, the elastic force; 

 OB, the damping force; OC, the inertia force; OD, the sustaining force; OP, the resultant of 

 OD and OA; <p, the phase angle; co, angular velocity; t, the time. B, relative values of tension 

 and length during a lo-msec. cycle of the model system for a positive phase angle, doHed, 

 and negative phase angle, solid. ±Po, maximum and minimum tensions; ±xo maximum and 

 minimum lengths; ¥>, phase angle. C, dynamic tension-length relation for the model system, 

 solid line, apd for the muscle, dashed line. E, minimum length, F, maximum length, O, equi- 

 librium point. See text. 



sustaining force OD opposed the damping force and is opposite to it on the dia- 

 gram. Applying cqiialion /, these forces must be balanced during the cycle. The 

 maximum force vectors are imagined to rotate counter-clockwise about the 

 zero point, with the same angles maintained between them. The force at any 

 instant is the j^rojection of the vector upon the line LS, the direction of motion; 

 e.g. OA', OB', etc. The cycle is considered to begin when length is maximum. 



