A transmission device for a cycle, such as a bicycle, which includes a bottom bracket fixed relative to the remainder of the cycle frame. The device includes a cylindrical main body centered about a first axis and a secondary body centered about a second axis, the second axis being parallel to, but not merged with, the first axis; a crankset rotationally mounted along the first axis relative to the main body and including a pair of cranks, a first circular toothed element and a second circular toothed element, both being centered on the first axis; a chainwheel rotationally mounted along the second axis relative to the secondary body and including a third circular toothed element and a fourth circular toothed element, both being centered on the second axis; the first and third toothed elements and the second and fourth toothed elements constituting a first gear train and a second gear train, respectively; a disengageable blocking device provided to block, selectively, the rotation of the first toothed element relative to the crankset or the rotation of the third toothed element relative to the chainwheel, on the one hand, and the rotation of the second toothed element relative to the crankset or the rotation of the fourth toothed element relative to the chainwheel, on the other hand.

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