In the Kardashian family, there’s no such thing as being afraid to show your body on social media. On Instagram, celebs’ favourite place to express themselves, the eldest one of the Kardashian sisters, Kourtney, proved herself to be sexier than ever in a swimsuit. So step aside, Kim - because 39-year-old Kourtney showed to her 67.9 million followers that she still has a dream body and it would be a shame to cover it up.Next to her friend Larsa Pippen, the star posed on a mattress in a black bikini. Proud of her tan and curves, she seems rather at ease. The internet loved the picture with more than 800, 000 likes: ‘Sexy’, ‘Kourtney is perfect as always’, ‘You’re so natural and beautiful’. And it's no wonder she remains in such a fit shape, as she reveals how she keeps up such a slim, toned bod at a trim 98lbs (7st). Sharing on her pay app KourtneyKardashian.com, the mum-of-three reveals that she does 30 box jumps a day as part of her exercise routine, as she sweats it out even on vacation. The star particularly likes to pay attention to the glutes and hamstrings, explaining how the box jump squats are perfect for a good cardio burn. In fact, even her sister Khloe Kardashian affirms that the hot mum is a "badass" in the gym. Whilst Kourtney is more open about her strict diet plans compared to her daily workouts, she says she relies upon simple full-body workouts to give her muscles the burn that they need all the while keeping her slim and toned. It's also no secret that social media and TV personality loves outdoor activities such as hiking (something to get that vitamin D in as well) whilst dabbling in other fun activities such as boxing to keep up her cardio. It's absolutely no wonder the eldest of the Kardashian sisters shamelessly rocks any bikini, as she often dazzles on her social media. Keep being a badass, Kourtney!