I'm sure this is baked somewhere but I can't find it.
Human power generators generally come in two types, hand crank and foot crank, but there is a better way, pull cord.
Take a generator and hold it between your feet with loops around said feet. Have a pull cord connected to a two handed handle
and one way recoil on one side and gearbox and generator on the other.
You probably also need a basic set of rollers or skids that extend below your heels.
To operate the generator, sit down with the generator between your feet and perform a rowing motion with both your legs and arms. The generator will roll away from you on its small wheels while the pull cord spins the generator to create power.
You get the advantage of a using both your arms and you legs to create power without the disadvantage of having to bolt the generator down to use either hand or foot power.
It is basically like a rowing machine except you stay still and the generator rolls back and forth on little wheels under your heels. The design reversal drops the size down to something that could be carried around or stored easily as it should be a little bit over softball sized as you no longer need the rail and seat, though I guess you might fall over sideways.
About the only thing I have found is the OLPC laptop was supposed to come with a pull cord charger that never materialized and the GravityLight which used a falling weight to power an LED light.
To limit the need for a flywheel, it would also be a good idea to add a sizeable supercapacitor pack to the generator to store all the created energy and then slowly feed it out to recharge batteries or power LED lights.