All that effort seems like a bit of a waste
Dangerous thinking about the exercise bike , if you recall the Black Mirror episode "Fifty Million Merits".
But yes, unharnessed effort is a wonderful potential source of electricity generation. I'm a bit too reliant on a walking stick already due to arthritis linked to over exercising in previous decades. So I'd be looking at other potential sources. My best idea is the electricity generating bed. Compression and uncompression of mattress springs could be used to generate a current for device charging. Yes, you'd be working whilst you slept! And other more vigorous bed based activities would generate even more power.