The Betfair Hollywood Park spring-summer meeting will be five races old when jockey Patrick Valenzuela walks into the paddock to ride the maiden claimer Family and Friends in a sprint Thursday. For Valenzuela, 49, the mount will be the first in the latest comeback of his career, four months after he announced his retirement from riding because of knee trouble and gall bladder surgery. Valenzuela, whose career has been interrupted repeatedly in the past because of substance-abuse problems, may have a big week in the first days of the Hollywood Park meeting. Friday evening, he rides Acclamation, the champion older male of 2011, in the $100,000 Inglewood Handicap, the horse’s first start of 2012. “I’m very confident and very optimistic,” Valenzuela said in a phone interview Tuesday morning. “I’ll try to come back the same way I have in the past, with some winners.” Valenzuela, who has won 4,333 races in his career, has not ridden since November. A month later, he announced his retirement, insisting he would not change his mind. He announced his comeback earlier this month. The condition of his knees, more than 33 years after his first win in New Mexico, remains a concern, he says. A recent exercise program that includes Bikram Yoga may help, he hopes. “That is some tough stuff,” he said. “It’s like doing yoga in a sauna room. “I think it’s helping my knee, too. The teacher tells me it does.” By incorporating yoga into his exercise away from the racetrack, Valenzuela said he hopes to “strengthen his legs and take the strain off the knees. “So far, I’ve felt good. I’m eating the right food after having my gall bladder removed. I had to change my diet.” Valenzuela has two mounts on Thursday afternoon and four on Friday evening. Last week, he worked Acclamation on Santa Anita’s turf course. Last year, Valenzuela rode Acclamation to two stakes wins, including the $1 million Pacific Classic at Del Mar. “He worked like a monster, the way he worked the other day,” Valenzuela said. “I hope he does what he did last year.”