definitely sweated turning 60 – but luckily her friends were along for the ride.
Clad in a bright yellow headband and exercise clothes, the birthday girl – whose big day is Wednesday – invited about 50 of her friends to join her for a spin class followed by sweet treats at West Hollywood's SoulCycle on Friday.
"[There were] no celebs, just her own friends," an onlooker tells PEOPLE. "Oprah was in the best mood. She was smiling and in such a celebratory mood. It seemed like she was having a great time with her friends."
But what's all that hard work without a little fun?
"They did a class for 45 minutes, and for about another 45 minutes they all mingled and enjoyed candy, cupcakes and juice," the onlooker adds. "They all wore customized T-shirts that said, 'Happy Birthday Oprah.' "
And it looks like the fitness fete was a success. In a short clip
posted to her Instagram page, Oprah is surrounded by her cheering guests as she whips her white towel around and says, "I just had the best birthday experience ever at SoulCycle. Ride, baby, ride, SoulCycle."