Seemingly easy idea.
As per Uswitch 40GWh of energy is generated by the UK gym population every year.
Retrofit gym machines with a device that captures some of this electricity.
https://www.uswitch.com/gas-electricity/guides/how-much-energy-is-generated-in-the-gym/
Business case can be around carbon credits to subsidise installation, electricity generation, cheaper gym memberships, cheaper operating costs for the gym etc
