Final answer:
The left ventricle has the thickest musculature because it must generate high pressure to pump blood through the systemic circuit.
Step-by-step explanation:
The chamber of the heart with the thickest musculature is the left ventricle. This is because the left ventricle needs to generate a high amount of pressure to pump blood through the long systemic circuit, overcoming greater resistance compared to the pulmonary circuit which the right ventricle pumps into. The left ventricle's myocardium is significantly thicker than that of the right ventricle, enabling it to pump blood effectively to the entire body.