Hand crank assisted bicycle

Adding a set of pedals might give us a more varied workout but it cannot help us go any faster.

The amount of energy we can draw on to propel our bicycles is limited not by how much muscle we can bring to bear but by the amount of fuel we can burn which is in turn restricted by the amount of oxygen we can process. Bigger lungs and/or better lung function will allow us to go faster but extra pedals for our front limbs will just add unnecessary weight and actually slow us down. This idea gets rolled out every twenty years or so as each new generation of inventive geniuses discovers bikes and decides to improve them. Bicycles so equipped didn't go any faster a hundred years ago. They still don't.