Question

during which phase are calcium ions actively transported into the sarcoplasmic reticulum?
relaxation
contraction
excitation - contraction coupling
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Explanation:

During muscle relaxation, calcium - ATPase pumps actively transport calcium ions from the sarcoplasm back into the sarcoplasmic reticulum. This reduces the calcium ion concentration in the sarcoplasm, allowing muscle fibers to relax. In contraction, calcium ions are released from the sarcoplasmic reticulum, and during excitation - contraction coupling, calcium ions play a role in linking the electrical signal to muscle contraction.

Answer:

Relaxation