I thought about this thing before.
I discovered the phenomenon of energy recovery in fixed gear transmissions.
The wheel is essentially a flywheel, and the flywheel is a mechanical energy storage.
In the fixed gear, the flywheel is rigidly connected to the connecting rods from which the accumulated energy is removed without the clutch only with the help of the legs.
Usually, the calculations take the action of kinetic energy when moving along a plane, forgetting about the potential energy on descents.
In addition, a transmission with a countershaft multiplies the internal stored energy in comparison with conventional transmissions.
The energy of the cyclist on the descent is spent on overcoming the air resistance, and the included free travel of the clutch when moving by inertia does not allow to increase the speed and twist the cranks (pedals).
On the NewFixedGear transmission, it is always possible to twist the cranks (pedals) and on the descent it is not so difficult, because the work of the potential energy of the descent is included in the work of the entire rider-bike system.