Tuesday saw Prince William celebrate his 40th birthday, and while we don’t know how he and his wife the Duchess of Cambridge celebrated, we do know the royal will need to make some changes to stay fit in his new decade.
MORE: Prince William releases personal message on 40th birthday
The Duke of Cambridge has always been an active man, and just last month he wowed fans with his biceps during an official engagement, but now that he's in his forties, he might find that recovery from exercise takes longer than it did in his younger years.
WATCH: Prince William visits England Women at St George's Park
"As we reach our forties, we need to be aware that our recovery time may take a little longer," says Omar Mansour, ambassador for audio fitness app WithU.
MORE: Prince William celebrates milestone 40th birthday with never-before-seen photos
REVEALED: The Queen's generous 40th birthday present to Prince William
"In our forties, our metabolism begins to work less effectively and muscles and ligaments get tighter, so it is essential we adapt our fitness regime to compensate the changes happening in our body," Omar continues.
Hormones such as testosterone can also decrease during our forties, Omar warns. "Strength training has been proven to increase testosterone levels in males, so is a great style of training to incorporate."
Prince William revealed his toned biceps on a hospital visit
Now in his fifth decade, Prince William should focus on a mix of endurance and strength training, according to Omar. "This will not only boost his cardiovascular fitness but also enables efficient calorie burn throughout the day. "
MORE: How Prince William and Kate Middleton prioritise their children over royal duties
Omar also recommends the Duke of Cambridge work yoga and Pilates into his workout schedule.
Prince William has always been active, enjoying football on occasion
"In our forties our muscles and ligaments naturally get tighter so it is important to keep them active with gentle workouts that will help prevent injury and wear and tear," he says. "Ensuring he takes time to warm up and cool down will help preserve his joints and tissues and make sure he has longevity in his training."
READ: Why Kate Middleton wants Prince George and Princess Charlotte to follow in her sporting footsteps
As for exercises, the royal should avoid in his fourth decade, Omar said Prince William should be okay to keep going as he is. "There is no exercise that is completely off-limits but just be sensible!" Omar says.
"As a seasoned exerciser, he won't need to dramatically change his routine, just make small adjustments to safeguard his body."
Make sure you never miss a ROYAL story! Sign up to our newsletter to get all of our celebrity and royal news delivered directly to your inbox.