The impact of myotonia on muscle performance in Mbnl1−/− mice was assessed by ex vivo force-contraction recordings in soleus muscles isolated from adult (4–6-month-old) WT, ClC-1ΔE7a, Mbnl1−/−, and Mbnl1−/−; ClC-1ΔE7a mice. The gene discussed is MBNL1; the disease is Myotonia.