Sure, cycling is more efficient kcal/km wise, but at least the speed that I and most people I know cycle is more intensive than walking kcal/second.

The sit ups: http://en.wikipedia.org/wiki/Sit-up_(exercise) I don't know if the same applies to hanging sit ups, but this Wikipedia article says:

> Situps can be dangerous due to high compressive lumbar load[1] and may be replaced with the crunch in exercise programs[2].