A multifunctional arm cranking exerciser, comprising: an omnidirectional support bracket assembly, which comprises a top end to which a five-way bracket is fixedly mounted, the omnidirectional support bracket assembly allowing the multifunctional arm cranking exerciser to be attached to an existing or a separately purchased leg exerciser to form a hand and leg exerciser; a left arm exercising device, which is mounted to a left side of the five-way bracket; a right arm exercising device, which is mounted to a right side of the five-way bracket; a damping adjustment device, which is mounted on the five-way bracket and generates and applies damping or a resisting force to the left arm exercising device and the right arm exercising device, and is operable for adjustment of the damping or the resisting force in order to achieve an effect of efficient exercising, characterized in that the exerciser comprises a quick release pin device, which is operable for selectively quick coupling and positioning of left and right arm cranks (25, 35) of the left and right arm exercising devices (20, 30) at an angular difference of 0 degrees for synchronous movement or at an angular difference of 180 degrees for linked, collaborative movement or for selectively quick release and decoupling of the left and right arm exercising devices (20, 30) for independent operation; and in that the omnidirectional support bracket assembly comprises two tubular bodies extending downward from the five-way bracket and the two tubular bodies are respectively provided, on lower ends thereof, with a first curved tube and a second curved tube rotatably mounted thereto such that the first and second curved tubes (131, 132) are rotatable, for 360 degrees, to optimum positions, wherein the first curved tube comprises a first swivel terminal rotatably mounted to a lower end thereof and the first swivel terminal comprises a first swing member rotatably mounted to a lower end thereof so that the first swivel terminal is allowed for rotation through a range of 360 degrees for an optimum angular position, and the first swing member is allowed to swing or rotate in a front-rear direction for a range of 340 degrees; and the second curved tube comprises a second swivel terminal rotatably mounted to a lower end thereof and the second swivel terminal comprises a second swing member rotatably mounted to a lower end thereof, so that the second swivel terminal is allowed for rotation through a range of 360 degrees for an optimum angular position, and the second swing member is allowed to swing or rotate in a front-rear direction for a range of 340 degrees, wherein the first and second swing members (151, 152) are attachable to a separately purchased or existing leg exerciser. an omnidirectional support bracket assembly, which comprises a top end to which a five-way bracket is fixedly mounted, the omnidirectional support bracket assembly allowing the multifunctional arm cranking exerciser to be attached to an existing or a separately purchased leg exerciser to form a hand and leg exerciser; a left arm exercising device, which is mounted to a left side of the five-way bracket; a right arm exercising device, which is mounted to a right side of the five-way bracket; a damping adjustment device, which is mounted on the five-way bracket and generates and applies damping or a resisting force to the left arm exercising device and the right arm exercising device, and is operable for adjustment of the damping or the resisting force in order to achieve an effect of efficient exercising, characterized in that the exerciser comprises a quick release pin device, which is operable for selectively quick coupling and positioning of left and right arm cranks (25, 35) of the left and right arm exercising devices (20, 30) at an angular difference of 0 degrees for synchronous movement or at an angular difference of 180 degrees for linked, collaborative movement or for selectively quick release and decoupling of the left and right arm exercising devices (20, 30) for independent operation; and in that the omnidirectional support bracket assembly comprises two tubular bodies extending downward from the five-way bracket and the two tubular bodies are respectively provided, on lower ends thereof, with a first curved tube and a second curved tube rotatably mounted thereto such that the first and second curved tubes (131, 132) are rotatable, for 360 degrees, to optimum positions, wherein the first curved tube comprises a first swivel terminal rotatably mounted to a lower end thereof and the first swivel terminal comprises a first swing member rotatably mounted to a lower end thereof so that the first swivel terminal is allowed for rotation through a range of 360 degrees for an optimum angular position, and the first swing member is allowed to swing or rotate in a front-rear direction for a range of 340 degrees; and the second curved tube comprises a second swivel terminal rotatably mounted to a lower end thereof and the second swivel terminal comprises a second swing member rotatably mounted to a lower end thereof, so that the second swivel terminal is allowed for rotation through a range of 360 degrees for an optimum angular position, and the second swing member is allowed to swing or rotate in a front-rear direction for a range of 340 degrees, wherein the first and second swing members (151, 152) are attachable to a separately purchased or existing leg exerciser.