The former Spice Girls singer - who gave birth to third daughter Madison, her child with husband Stephen Belafonte, in September - is renowned for her trim physique but has to keep altering her exercise routine to stay motivated.
She said: "Of course it`s an effort! The hardest part is getting yourself to the gym. Once I`m there, I just do it. It`s literally just a case of getting myself there.
"Sometimes I run, sometimes I do weights, sometimes I go take a class, sometimes I`ll take a hike outdoors. I mean, it really depends on what mood I-m in."
Mel - who also has daughters Phoenix, 12, and Angel, four, from previous relationships - advised women hoping to regain their pre-pregnancy figures to work out an eating plan and establish a consistent exercise regime.
She told Britain`s Star magazine: "I don`t know one woman who doesn`t want to be back at the size she was before she was pregnant. Every woman wants to be back at the same size.
"It`s just a case of dedicating yourself and just trying to be somewhat consistent with trying to work out your eating plan and everything else."