The excessive muscle mass serves as both the Tank's weapon and armor.

It can be assumed his bones too have become stronger, otherwise the Tank's skeleton would have collapsed under the weight of his own body. The Tank's jaw at first glance seems to be missing, but upon closer inspection it is shown to be enveloped within his thick neck muscles. The Tank's body is covered with numerous scars and lesions from previous fights, with an especially large open sore on his left pectoral. Though the Tank's legs are capable of supporting his static weight (such as when the Tank mounts a rock throwing attack), the Tank's disproportionate anatomy forces him to knuckle-walk, resulting in the Tank's wrists becoming swollen. This abnormal muscular growth is most obvious in his arms and upper body but less pronounced around the Tank's waist, hips, and legs. According to the Left 4 Dead 2 Survivors' dialogues, the Tank is around 10-12 feet tall and 6 feet wide. Ironically, the Tank is incredibly fast and agile despite his immense size and weight, able to keep up with a healthy Survivor and even climb up buildings like other Infected. Evidently, the most obvious trait is his extreme hypertrophy, or abnormally increased muscle mass. The Tank is an exclusively male Special Infected who has experienced the most extensive physical mutations of any other class of Special Infected.

Sourcemod l4d2 tank idle