question about abs/ core
i know mark says for strong abs/ core, you just contract your abs during activities through out the day. since it's only for 10-20 seconds or so at a time, are you supposed to have days off in between days that you randomly contract your abs? or should i contract my abs every day through out the day? thanks in advance.
you do not need to worry about taking days off from 'randomly contracting your abs.'
full body compound movements will give you great abs - squats, deadlifts, pullups. to recover from movements like that, you need days off. not for randomly flexing muscles.