Patrick Schwarzenegger says he got up at 5 AM to workout for the 50 days, and it's helped him build muscle and lose fat.
The actor, model, and entrepreneur wrote on Instagram that he's gained 22 pounds and cut his body fat percentage from 13% to 8%.
"Getting in the best shape of my life. Both physically & mentally," Schwarzenegger said.
Schwarzenegger wrote on Instagram that he exercised at 5 AM for 50 days to build momentum for the day, to motivate his mind and body by doing something hard, and to form a habit that led to progress over time.
Personal trainer and coach at CrossFit Putney in London, Sarah Molloy, told Insider that early workouts can work well for busy people.
"It's amazing how quickly it becomes a routine, especially if you are meeting the same group of friends at the class," she said. "You look forward to that hour with them so getting up early is not a chore and that helps to make it sustainable."
Molloy said many people have more energy in the morning so their gym performance is better than in the afternoon.
Elliott Upton, personal trainer at Ultimate Performance and Head of LiveUP Online Coaching, told Insider that exercising in the morning can be beneficial because it pumps blood around the body and brain, releases endorphins, reduces stress, and makes you more productive.
"It creates a positive feedback loop which will improve all aspects of your health, recovery, training, and nutrition," Upton said.
While there isn't much large-scale research that analyzes how time of day impacts exercise, a small 2012 study conducted by Brigham Young Unviversity suggests morning workouts lead to moving more over the course of the day, and this small 2014 study conducted by Appalachian State University researchers found early workouts led to better sleep.
Whether you want to transform your body or just live a healthier lifestyle, working out at 5 AM is "not necessary," Upton said, adding that training frequency and consistency is more important than timing.
"Working out when you are able to perform your best and get the maximum output from your training is always going to be the most important factor," he said.
Every person is different, and it's better to workout when you feel your best, than to try to force your body to exercise based on someone else's routine.
"Some people are morning people and some are night owls, all dictated by your body clock," Molloy said.
"It's all individual and, as long as you're finding the time and it's a time when you're feeling at your optimum, and able to enjoy it, then do what is best for you," Molloy said.
She suggests training at different times of day for a few weeks to track your energy levels, to see how you feel afterwards, and to gauge whether you enjoyed your workout or if it was too much of a struggle.
Consider how your training timing fits into your eating habits, too. Molloy said it's best to be well fueled for a weight-lifting session, but a morning walk or swim might be OK on an empty stomach.
Gaining muscle while losing fat is known as "body recomposition" and is notoriously challenging, especially if you're experienced when it comes to working out, experts previously told Insider.
Strength-training is only one part of the puzzle, and dialing in on your nutrition is key — you need to be eating the right amount, including plenty of protein, Upton said.
In a recent video for Men's Health, Schwarzenegger said his diet generally consists of:
He added that he used to workout while fasting, but now always eats before training to help with performance and muscle-building.
"Once you figure out your training timings then 'eat to perform,'" Molloy said.
"If you're training early in the morning, then eat a good meal with carbs the night before, so if you only have time for a small snack like a banana pre-workout, you've still got fuel in the tank."
If you're training later in the day, she recommends leaving enough time for your lunch or dinner to digest before working out.
"And if you know you'll be constantly on the go after training, then always pack protein-rich snacks or shakes to have after," Molloy said.
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