Figure 4
Differential axial and transverse responses following multiple cycles of stretching. Changes in peripheral areas are measured at the 1st cycle, 2nd cycle, and after various periods of cyclic stretching at 0.5 Hz as shown in the diagram, where the timing of image acquisition relative to the stretching cycles is indicated by red crosses. Local retractions or protrusions of different quadrants are then integrated and normalized against the total spreading area to reveal net extension (positive values) or retraction (negative values). Note that while the relaxation phase lasts for 1 s for cyclic stretching at 0.5 Hz, given the slow, persistent nature of extension, net extension was measured over a period of 10 s to improve the accuracy, after halting the cyclic stretching. Therefore, the actual extension during the relaxation phase is approximately 10% of the values shown in the upper graph. Net retraction takes place immediately after stretching (lower graph), while net extension takes place during subsequent 10 s of relaxation (upper graph). Moreover, net extension of axial quadrants decreases progressively with increasing cycles of stretching (top orange), while net extension of transverse quadrants remains constant (top blue). Retraction occurs similarly in all the quadrants, showing a strong response following a single cycle of stretching and a precipitous decrease with additional cycles of stretching (bottom graphs) (*p < 0.05; **p < 0.01; n = 16–20, mean ± SEM).
