A single motor power unit, suitably for being mounted in a bicycle frame so to provide a bicycle having a crank shaft with a motor-driven system and a manually driven system in parallel, the single motor power unit is fitted with: a motor, related power supply, bearings, crank shaft pinion gearhead, propulsor pinion gearhead, planetary gearbox and central processor unit, where the crank shaft pinion gearhead is configured to be connected to a crank shaft of a bicycle through the bearings, and the central processor unit is in wired or wireless connection with the motor, characterized in that the propulsor pinion gearhead is connected to a pinion with a dynamometric system, having an at least approximately identical axis, and to the planetary gearbox therethrough such that the pinion with the dynamometric system is located between the planetary gearbox and the propulsor pinion gearhead, while the inside of the bearings is in fixed connection with the crank shaft and the outside of the bearings is in fixed connection with the crank shaft pinion gearhead, further characterized in that when the single motor power unit is operating, the motor drives the propulsor pinion gearhead through the pinion with the dynamometric system, which is connected to and driving the crank shaft pinion gearhead, further characterized in that the pinion with the dynamometric system ensures that the single motor power unit does not break when the motor drives the crank shaft but movement of the crank shaft is prevented, further characterized in that the bearings are configured such that the motor and the propulsor pinion gearhead are disconnected from the crank shaft when the crank shaft is driven by manual pedalling and overruns the crank shaft pinion gearhead, further characterized in that the pinion with dynamometric system is configured to protect the propulsor pinion gearhead from damages when the crank shaft rotates suddenly in opposite direction driven by sudden manual backward pedalling or changes torque abruptly caused by interruptive manual pedalling, and further characterized in that the central processor unit comprises one or more of an electro-mechanical button, a heart rate meter, a rotation meter, and a speed meter, and further characterized in that the central processor unit causes a startup and shutdown of the motor when the central processor unit receives and processes one or more signals from the one or more of the electro-mechanical button, the heart rate meter, the rotation meter, and the speed meter. a motor, related power supply, bearings, crank shaft pinion gearhead, propulsor pinion gearhead, planetary gearbox and central processor unit, where the crank shaft pinion gearhead is configured to be connected to a crank shaft of a bicycle through the bearings, and the central processor unit is in wired or wireless connection with the motor, characterized in that the propulsor pinion gearhead is connected to a pinion with a dynamometric system, having an at least approximately identical axis, and to the planetary gearbox therethrough such that the pinion with the dynamometric system is located between the planetary gearbox and the propulsor pinion gearhead, while the inside of the bearings is in fixed connection with the crank shaft and the outside of the bearings is in fixed connection with the crank shaft pinion gearhead, further characterized in that when the single motor power unit is operating, the motor drives the propulsor pinion gearhead through the pinion with the dynamometric system, which is connected to and driving the crank shaft pinion gearhead, further characterized in that the pinion with the dynamometric system ensures that the single motor power unit does not break when the motor drives the crank shaft but movement of the crank shaft is prevented, further characterized in that the bearings are configured such that the motor and the propulsor pinion gearhead are disconnected from the crank shaft when the crank shaft is driven by manual pedalling and overruns the crank shaft pinion gearhead, further characterized in that the pinion with dynamometric system is configured to protect the propulsor pinion gearhead from damages when the crank shaft rotates suddenly in opposite direction driven by sudden manual backward pedalling or changes torque abruptly caused by interruptive manual pedalling, and further characterized in that the central processor unit comprises one or more of an electro-mechanical button, a heart rate meter, a rotation meter, and a speed meter, and further characterized in that the central processor unit causes a startup and shutdown of the motor when the central processor unit receives and processes one or more signals from the one or more of the electro-mechanical button, the heart rate meter, the rotation meter, and the speed meter.