Michael Crabtree and OTA practices.

For 49ers’ fans, those are cringe-worthy collection of words.

Crabtree, of course, sustained a complete tear of his Achilles at an OTA practice just over a year ago and missed the first 11 games of 2013.

So it might come as a surprise to some that Crabtree was involved in today’s practice – the first session open to the media – given his recent past.

Crabtree, however, retreated to the locker room with about 45 minutes left in the two-hour practice and Jim Harbaugh said the 49ers are taking a cautious approach with the wideout.

“There’s a plan in place for him,” Harbaugh said. “More limited than some of the receivers that we have. I think our medical staff, and Michael, and we as coaches are taking a smart approach.”

Early in practice, Crabtree dropped back-to-back passes in the end zone during a red-zone drill. When he caught the next ball thrown to him, he flung the ball skyward in mock celebration.

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Tight end Vernon Davis was not in attendance and “hasn’t been here much at the facility” during the offseason, Harbaugh said.

Why? “As you know, the workouts are voluntary,” he said. “That would be the reason.”

Harbaugh also cited the “voluntary” workouts when asked about right guard Alex Boone’s absence. Boone reportedly is not attending because he’s dissatisfied with his contract.

Running back Frank Gore has not attended practices, but has been working out at the facility.

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Wide receiver Stevie Johnson was not in attendance because he has a “little something he’s working through” said Harbaugh, who clutched his hamstring as he explained Johnson’s absence.

Tackle Jonathan Martin, who has had mononucleosis for nearly a month, was a spectator at practice. Harbaugh indicated Martin is close to returning.

Wide receiver Jonathan Baldwin (undisclosed) was also a spectator and nose tackle Ian Williams, who broke his ankle in September, was at the facility but did not practice.

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Cornerback Chris Culliver, who tore his ACL last year in training camp, has been participating in practices, although he did not practice today. Harbaugh expects Culliver to be full participant at training camp.

In Culliver’s absence, Eric Wright and Chris Cook assumed his spot before Wright sustained what appeared to be a minor ankle injury.

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The well-sculpted Colin Kaepernick doesn’t appear to have added any body fat in the offseason. And Harbaugh has noticed.

“I really expect a real breakout year for Colin,” Harbaugh said. “Athletically, he looks bionic. If you all remember The Six Million Dollar Man? That’s what it looks like to me. He’s very gifted and he always has been. He has the look and feel of a guy that’s really going to break out, even more so than he already has. I’m excited about everything about his game.”

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It appeared Marcus Lattimore, who participated fully in practice, was running a bit cautiously, but it’s difficult to discern in an OTA practice. Harbaugh said Lattimore is still working his way back from a hamstring injury, but his surgically repaired knee is “good.”

“He strained his hamstring a few weeks back,” Harbaugh said. “He’s really been coming back from that day by day, more so than from the knee. Talk to him and the knee feels good. He’s getting back, getting the hamstring back.”

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Two moments during today’s practice inspired cheers from the players.

First, linebacker Patrick Wills was applauded after he intercepted a close-range, high-velocity pass over the middle from McLeod Bethel-Thompson and took off running for an imaginary touchdown.

Then, defensive tackle Lawrence Okoye, 6-foot-6 and 304 pounds, drew even bigger cheers – and several high-fives – when he tracked down cornerback Darryl Morris during a punt-return drill. Morris ran a 4.33-second 40-yard dash at his pro day last year at Texas State and was offered partial track scholarships by LSU, Texas and Houston.

“The fellows were – they liked that,” Harbaugh said. “That was one of the high points of practice watching Lawrence run down on kickoffs. And he’s been doing that for us. He’s a big guy and he can run. Like a lot of guys, trying to find their spots. Trying to find their role. That’s a place that he’s working in right now. It would be fun to watch, wouldn’t it? Big 300-however-many-pound guy down on kickoffs. I’d love to see it.”