She’s openly documented her gruelling fitness regime, and Jennifer Lopez had her toned abs on full display as she headed to the gym on Monday.The singer, 57, was dressed in a nude crop top and matching leggings and carried her essentials in a £22,000 Birkin bag.Jennifer has previously given insight into her fitness regime and has shared snaps with her fans while she worked out at the gym.’You know that you’re gonna be on screen. You gotta be prepared… in the gym and eating right,’ she told Extra in June.’It’s about eating healthy and eating the right things and working out and being consistent. I say these things all the time.’She also focuses on weight training in order to keep her muscles strong, and explained on CBS Mornings that she now focuses on a workout routine that is ‘smarter, not harder.’ She’s openly documented her gruelling fitness regime, and Jennifer Lopez had her toned abs on full display as she headed to the gym on Monday’That’s what my trainers and I think about a lot. It’s like, I have 40 minutes for you right now and we need to maximize that, and we do.’Lopez added, ‘I lift heavy, I do a lot of weights now because as you get older you need to start doing that in your 30s.’And you need to do that because, even if you’re like, into cardio and you want to be slim or drop weight or whatever, muscle is the thing that burns fat.’The music artist further explained that ‘as we get older, we lose the muscle. So, we need to build the muscle to keep a youthful appearance, you know?’It comes after it was reported that friends were concerned for the star, amid fears she may be headed towards ‘burning out’ by taking on too much work. The On The Floor hitmaker has scooped an eye-popping $20million (£14.7million) deal with Dolce & Gabbana, been planning a world tour, acting and plugging her movies. Friends are said to be concerned that her workload is giving echoes of the nervous breakdown she suffered in 2002 and are desperate to avoid history repeating itself.The Daily Mail learned that the mother-of-two will be the new face of Dolce & Gabbana, while she is also planning an international tour for next year. The singer was dressed in a nude crop top and matching leggings and carried her essentials in a £22,000 Birkin bagThe latest in her jobs are all in addition to the two movies she will have to promote – The JLo Show, about her recent Las Vegas residency, and the upcoming crime thriller The Last Mrs Parrish.Insiders revealed: ‘She is working her tail off because she wants to stay busy, though there is some concern she may burn out. ‘But this is how she stays sane during this weird time in her life.’Jennifer’s workload comes after her painful divorce from Ben Affleck as well as her twins Max and Oskar, formerly known as Emme, heading off to college.The insider continued: ‘It’s not an easy time for Jennifer, there are a lot of changes, it’s very emotional, but she finds comfort in working nonstop, which is great because her career is still doing very well… ‘She just works, works, works! She likes to be a workaholic, she is incredibly driven, a typical Type-A Leo who wants to never be out of the spotlight…’For her, working is better than staying at home eating takeout from Nobu alone in front of the TV. She would rather wake up at 5am and put in a 14-hour day and never complain,’ said the source. ‘But one day she may wake up completely exhausted.’Jennifer previously revealed how she reached breaking point in 2002 while filming the thriller Enough, in which she played an abused wife trying to flee to safety with her young daughter.In a 2008 interview with The Daily Telegraph, she said: ‘There was a time when I was very overworked and I was doing music and movies and so many things…’I was suffering from a lack of sleep. And I did have a kind of nervous breakdown. I froze up on set. Well, not on a set, but in my trailer…’I was like – I don’t want to move, I don’t want to talk, I don’t want to do anything. It was on that movie, Enough. Yeah, I did. I had a nervous breakdown.’