Isometric force decline.

<p><i>A, B and C</i>: Representative tracings of the isometric relaxation curves after 0 s (<i>A</i>), 100 s (<i>B</i>) and 300 s (<i>C</i>) of the exercise protocol. Note the time lag before force decline starts (marked with ¤) due to time required for relengthening. The transient slowing of isotonic relengthening peaked after 100 s of stimulation (confer <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022695#pone-0022695-g002" target="_blank">Figure 2C</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022695#pone-0022695-g003" target="_blank">3F and G</a>). Sham in black and chf in gray. <i>D and E</i>: Time constants (tau1 (<i>D</i>) and tau2 (E), average values for sham (n = 22) and chf (n = 24)) from the isometric force decline at 0, 100, 300, 450, 600 and 900 s of stimulation calculated from a fitted biexponential decay curve. Error bars are ± SEM. Sham in black and chf in gray. †p<0.05 vs. sham. <i>F</i> and <i>G:</i> Averaged force recordings (y-axis) during the period of relaxation (isotonic and isometric phases, x-axis), assembled for the first 5 min of exercise (z-axis) for sham (<i>F</i>, n = 22) and chf (<i>G</i>, n = 24). The time period for relengthening before force decline starts is indicated (black line marked with ¤, confer same symbol in panel <i>A</i>, <i>B</i> and <i>C</i>). T_bl is indicated with a red line. Note the transient rise after 100 s in both groups (confer <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022695#pone-0022695-g002" target="_blank">Figure 2B</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0022695#pone-0022695-g003" target="_blank">3A, B and C</a>). Since there is no difference between the two groups regarding the isotonic relengthening (black line, <i>F</i> and <i>G</i> (¤)), the attenuated increase in T_bl in chf compared to sham after 100 s (red line, <i>F</i> and <i>G</i>) is due to differences in the isometric force decline.