And when this is done, these calcium ions are moved against the electrochemical gradient. And ultimately, what this also does is it reestablishes that electrochemical gradient that is needed for the protein channels to move the calcium back into this direction so that the muscle contraction, the next muscle contraction can actually take place. So we see that calcium is needed for muscle contraction. And during contraction, calcium flows into the cytoplasm of the cell from the sarcoplas reticulum lumen down into its concentration, down its concentration gradient. And once the contraction is over, to actually relax that muscle, these calcium ions must be sequestered back into the lumen of the sarcoplas reticulum. And this is done by these pumps because this actually requires energy to move these calcium ions against their electrochemical gradient.