Bike Riding , Is this all I will need to 'build-up'?

I do sit-ups every night (30, rest, 30 rest, 30, rest, etc;).

I was thinking of taking up running but I just saw a question on Bike riding, and it seems like a WAY better idea.

Bike riding won't make me feel like an idiot (I know it sounds strange but I'm quite self-concious and I'm thinking - Say if I saw someone I know when I'm running around the park, sounds silly... lol)

I could ride ym bike around my block/estate (It's around a quarter of a mile) What will bike riding do for me, will it ONLY build up my leg muscles? IF so will I need to do running also to tone the rest of my body, or do I need to just do some press-ups to build up my arms also?

What do you guys recommend? Should I:

• Bike riding for a fixed period?
• Running for a fixed period
• Both , swapping the training between different days.

(I will be doing sit-ups with both exercises) So, what do you guys think? Thank's in advance !
 
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