Abstract: A weight adjusting device (1) for a muscle training machine, which includes a hanger bar (30); weight plates (31) having a vertical central aperture for receiving the hanger bar; latch levers (32) attached to the weight plates for rotation in a horizontal plane between a release position and a latch position; lock levers (35) attached to the weight plates for rotation in a vertical plane between a lock position and an unlock position; spring means (3) placed between the latch lever and the weight plate so as to urge the latch lever toward the release position; interlocking arms (37) extending upwardly from a rear potion of the latch lever so as to contact another latch lever above the latch lever at right angles; latch notches (2) formed on a circumference of the hanger bar; and latch recesses (7) formed on the latch levers so as to engage the latch notches on opposite sides thereof when the latch lever is moved towards the latch position against the spring means.