Iron-Type Golf Clubs and Golf Club Heads

An iron-type golf club head comprising:

• a top surface, a sole, a heel, and a toe;
• a ball striking surface having a ball striking area, wherein the ball striking surface defines a heel-side boundary line, a toe-side boundary line, and a ball striking centerline located equidistant between the heel-side boundary line and the toe-side boundary line;
• and
• a rear surface opposite the ball striking surface, the rear surface having a blade portion and a muscle portion with the blade portion separated from the muscle portion by a blade interface, wherein the blade portion and muscle portion laterally extend across the rear surface and further with the blade portion extending from the top surface to the blade interface and with the muscle portion extending from the blade interface to the sole;
• wherein the blade interface forms a ledge providing a transition area between the blade portion and the muscle portion;
• wherein the muscle portion comprises a muscle portion height measured vertically from the sole to the blade interface;
• wherein the muscle portion further comprises a muscle height toe-heel ratio defined as a ratio of an average muscle portion height between the ball striking centerline and the toe-side boundary line over an average muscle portion height between the ball striking centerline and the heel-side boundary line;
• wherein the muscle height toe-heel ratio is between 1.5 and 3.

An iron-type golf club head comprising:

• a top surface, a sole, a heel, and a toe;
• a ball striking surface having a ball striking area, wherein the ball striking surface defines a heel-side boundary line, a toe-side boundary line, and a ball striking centerline located equidistant between the heel-side boundary line and the toe-side boundary line;
• and
• a rear surface opposite the ball striking surface, the rear surface having a blade portion and a muscle portion with the blade portion separated from the muscle portion by a blade interface, wherein the blade portion and muscle portion laterally extend across the rear surface and further with the blade portion extending from the top surface to the blade interface and with the muscle portion extending from the blade interface to the sole;
• wherein the blade interface forms a ledge providing a transition area between the blade portion and the muscle portion;
• wherein approximately 25% to 35% of a total surface of the muscle portion is defined between the heel-side boundary line and the ball striking centerline and approximately 65% to 75% of the total surface of the muscle portion is defined between the ball striking centerline and the toe-side boundary line.