The key statistics for the 49ers so far in training camp: 19 practices, 18 in pads, three "nutcracker" drills and seven injuries lasting a week or longer.

So far, tight end Delanie Walker (concussion), cornerback Terall Brown (toe), linebacker Patrick Willis (foot), running back Michael Robinson (groin), guard David Baas (foot), linebacker Parys Haralson (hip flexor) and wide receiver Brandon Jones (fractured shoulder) have missed or are expected to miss a week or more of camp, with Jones out for eight weeks.

That's led to talk in the local media about the physicality of San Francisco's training camp. But coach Mike Singletary said no was asked if he'd consider cutting back on the physical nature in the face of mounting injuries. "Not one bit," he said.

Singletary has backed off his "nutcracker" drill, which pits two similarly sized players between blocking pads spaced three feet apart. The players are instructed to run through each other.

The drill gets so intense coaches frequently jump in after a few seconds to keep players from fighting. However, after Baas went down last week with his foot injury (he's out indefinitely) Singletary has yet to schedule another "nutcracker."

For Singletary and his players, the constant hitting is meant to establish a mentality they hope to carry into the regular season.

"I don't know if you acclimate," linebacker Jeff Ulbrich said. "There's definitely a different mentality then being out here in shells (light shoulder pads). It's demanding, you have to develop that mentality that you are going to bring it every play or you are just going to get destroyed. It establishes a survival mechanism."

Since Singletary forewarned his players about the physical nature of camp during the offseason, many players prepared for it. Running back Frank Gore turned to his strength and conditioning coach from his University of Miami days for extra training. Linebacker Takeo Spikes spent a few weeks with a mixed martial arts specialist.

"I don't want to say I worked harder this year than I have in the past, but mentally, you have to prepare yourself for a challenge such as this," center Eric Heitmann said.

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NOTES: Wide receiver Isaac Bruce was held out of practice after getting poked in the eye Tuesday. ... Rookie quarterback Nate Davis got some time in team drills and threw consecutive completions to wide receivers Dominique Zeigler and Josh Morgan. ... Zeigler made the play of the day catching a 35-yard strike from Alex Smith.