The APS Journal Legacy Content is the corpus of 100 years of historical scientific research from the American Physiological Society research journals. This package goes back to the first issue of each of the APS journals including the American Journal of Physiology, first published in 1898. The full text scanned images of the printed pages are easily searchable. Downloads quickly in PDF format.

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8. Responses to large amplitude sinusoidal stretching were also studied in relation to our classification.

1. The effects of maximal tetanic contractions of varying numbers of motor units of the same type [slow (S), fast fatigue-resistant (FR), or fast fatigable (FF)] on the mechanical responses to muscle stretch were studied in the peroneus longus muscle of anesthetized cats. 2. Two types of stiffness measurements were made: 1) an average stiffness, defined as the tension change from the beginning to end of a 0.5-mm ramp stretch; and 2) a dynamic stiffness, defined as the ratio of peak-to-peak tension to amplitude of a maintained 85-microns sinusoidal stretch at frequencies of 10-80 Hz. 3. Contractions of slow and fast units elicited different increases in average stiffness. Type S units, although developing much smaller tetanic tensions than fast ones, produced a resistance to stretch comparable with or greater than that of fast units developing much higher tensions. 4. For comparable tetanic tensions, slow units also elicited a greater dynamic stiffness than fast units. During sinusoidal stretch, changes in muscle tension led changes in muscle length during contraction of S units, but the reverse was observed for frequencies 30-50 Hz during contraction of FF units. This suggests that the latter perform oscillatory work on the driving apparatus. 5. Type S units, whose low-threshold motoneurons are the first to be recruited, appear well adapted to play a role in posture and in slow movements because of the resistance they offer to forces tending to change joint position or to oppose the progression of slow movements.

1. The effects exerted on secondary endings by repetitive stimulation of single static or single dynamic fusimotor fibres were studied in nine tenuissimus spindles in cats. 2. The discharge of each secondary ending was recorded simultaneously with the discharge of the primary ending belonging to the same spindle. 3. All the nineteen static fusimotor fibres studied activated secondary endings. 4. Of eight dynamic fusimotor fibres, seven had no action on secondary endings. One dynamic fibre activated an atypical secondary ending which displayed some phasic sensitivity. 5. No difference in conduction velocity was found between static and dynamic fibres. 6. The implications of these observations for the mechanism of action of static and dynamic fusimotor fibres are discussed.