Running back Fred Jackson took the handoff and was in the midst of making his first step forward when linebacker Shawne Merriman was suddenly all over him.

"I didn't see him coming," Jackson said Tuesday, recalling what happened a day earlier during a Buffalo Bills full-team session at training camp.

Had this been a game, Jackson knows he would've been flattened. Fortunately, this was practice, and Jackson got away with being on the receiving end of a two-hand shove that still knocked him back a few steps.

What's unmistakable to Jackson regarding Merriman is quite simple: "He's back."

Indeed, he just might be. Five days into camp in suburban Rochester, Merriman is starting to look and feel like his old self again.

Lights out?

"Almost," Merriman said with a wink upon mention of the "Lights Out" nickname he picked up early in his career when he was one of the NFL's fiercest hitters. "I'm not going to say I'm back-back yet because we still have a lot of time before we really have to strap on the pads and go. But every day I'm feeling a little bit better."

That's good news for Merriman, who had been slowed by a series of injuries and distracted by contract squabbles and off-the-field questions for much of the past three years. And it's significant news for the Bills, who last November took a gamble on the three-time Pro Bowl selection by claiming him off waivers after being released by San Diego.

Last year, Merriman lasted no more than 15 minutes in his first Bills practice before he came up limping, hobbled by a sore right Achilles' tendon that led to him being placed on injured reserve.

This year, after being re-signed to a two-year contract on Jan. 1, Merriman hasn't missed a minute.

"To be quite honest with you, two months ago, I don't think anybody, maybe not even Shawne, had a vision of where he wanted to be and what he could do. We didn't," assistant head coach Dave Wannstedt said. "Was it going to be just walkthroughs, was it going to be half-speed tempo? And the guy has done everything that every other player on this field has done. That's been a real positive."

Merriman benefited from the extended layoff that came with the 4-1/2-month NFL lockout. Though he worked out on his own, the time off gave his body an opportunity to heal.

Part of his regimen included a six-week stint of mixed martial arts training with retired MMA stars Randy Couture and Chuck Liddell.

"I got leaner, dropped a couple of pounds. And it's helping me move a little better, too," Merriman said.

Now that he's healthy, he's also regained his drive to return to his once dominating form and help transform the Bills into winners.

"I've even more committed to rebuilding this thing and doing what these guys need me to do," Merriman said. "I know exactly why they brought me here."

The Bills took a chance on Merriman to help improve a patchwork defense that last year couldn't stop the run and had difficulty generating pressure. Buffalo finished in a three-way tie for 27th in the league with 27 sacks last year.

Merriman had more than half that number in 2006, when he had 17. That was in the midst of his heyday, when Merriman registered 39-1/2 sacks in his first three seasons.

Injuries caught up to him, as he's managed four sacks and appeared in just 18 games over the past three years. He played in only one game in 2008, when he had reconstructive knee surgery, and played sparingly in six games last year with the Chargers.

Calling this the healthiest he's felt in a long time, Merriman has a bounce in his step.

"Just being back on the field and doing something that I love to do for a living, that's why I can't stop smiling every day," Merriman said. "I'm one of the most playful guys over there in the huddle, even though I'm a vet."

Fellow linebacker Reggie Torbor has taken notice.

"He kind of reminds me of a rookie. His eyes are wide open," Torbor said. "He had the pedal to the floor and it's really impressive and contagious."

Merriman insists he has nothing to prove to his critics or anyone else except his teammates.

"I know personally that I can play. You can look on the film and see me playing," Merriman said. "But to be a factor to the point where these guys are going to benefit from me playing at my best, that's what I need to prove."