[3] This difficulty in relaxation leads to symptoms including cramps, stiffness, and discomfort in the muscles of the limbs and face.

[8] Diagnosis of BD begins with clinical evaluation of individuals for characteristic symptoms of cramping and stiffness of exercised muscles.

[3] Blood testing may be used to measure serum creatine kinase, which ranges from normal to slightly elevated in those with BD.

Individuals with BD have stiff muscles but normal EMG results (pseudo-myotonia), where no myotonic discharges are detected.

When a muscle is stimulated, Ca2+ is released from the sarcoplasmic reticulum into the cytoplasm where it binds to a protein called troponin.

[14] In BD, Ca2+ levels are high in the cytoplasm, which means Ca2+ can readily bind troponin, leading to muscles that are in an extended state of contraction.