Influence of Joint Angle on Residual Force Enhancement in Human Plantar Flexors

Figure 1. Typical example of changes in joint torque and joint angle as a function of time. The left panel shows the Short condition (from plantar flexion (PF) 15° to PF0°) and the right panel shows the Long condition [from PF0° to dorsiflexion (DF) 15°]. The blue line shows the Control trial (pure isometric contraction) and the red line shows the Residual force enhancement trial (isometric contraction after eccentric contraction). Joint toque, fascicle length and pennation angle were measured at the measurement point (i.e., 4.9 s after the onset of contraction). −15 indicates PF15.

Figure 2. Joint torque values observed in the Control and Residual force enhancement trials. Joint torque values observed in the Control trial (pure isometric contraction) are shown as a white bar, and those observed in the Residual force enhancement trial (isometric contraction after eccentric contraction) are shown as a black bar. The left panel shows the joint torque value obtained at plantar flexion (PF) 0° and the right panel shows the joint torque value obtained at dorsiflexion (DF) 15°. Values are presented as means ± standard deviation. * Indicates a significant difference (p < 0.05) between the Control and Residual force enhancement trials.

Figure 3. Relative values of joint torque (Residual force enhancement trial relative to Control trial), indicating the magnitude of residual force enhancement * indicates a significant difference (p < 0.05) in residual force enhancement between the Short and Long conditions.

Figure 4. Fascicle lengths in the Control and Residual force enhancement trials in the Short and Long conditions. Fascicle lengths observed in the Control trial (pure isometric contraction) are shown as white bars, and those observed in the Residual force enhancement trial (isometric contraction after eccentric contraction) are shown as black bars. The left panel shows the fascicle length obtained at plantar flexion (PF) 0° and the right panel shows the fascicle length obtained at dorsiflexion (DF) 15°. Values are means ± standard deviation.

Figure 5. Pennation angles in the Control and Residual force enhancement trials in the Short and Long conditions. Pennation angles observed in the Control trial (pure isometric contraction) are shown as white bars, and those observed in the Residual force enhancement trial (isometric contraction after eccentric contraction) are shown as black bars. The left panel shows the pennation angle obtained at plantar flexion (PF) 0° and the right panel shows the pennation angle obtained at dorsiflexion (DF) 15°. Values are means ± standard deviation.