ENGLEWOOD, Colo. -- A team that has already made four changes on the offensive line, as the Denver Broncos have over the last month, can expect to be tested week to week.

That is, at least until it shows what has been a problem is no longer a problem. And after an early-season sack drought -- one sack in the first five games -- the St. Louis Rams' defense has shown over the last four games that it can be a significant problem for an offensive line having some problems, its 3-6 record notwithstanding.

"You can't take these guys lightly," said Broncos wide receiver Emmanuel Sanders. "This is a good football team we're facing, with a good defensive line, speaking from an offensive standpoint, and we're playing them at [their] home."

The Rams have had their share of issues over the last three seasons, whether it be injuries, missed opportunities or too many mistakes at inopportune times. But the one constant has been the team's ability to put opposing quarterbacks in harm's way, with 105 sacks in the 2012 and 2013 seasons combined. More of the same was expected this season.

But the Rams opened the season with one sack -- in Week 2 against the Tampa Bay Buccaneers -- in their first five games combined.

"The ball was coming out very quickly," said head coach Jeff Fisher. "We had to adjust to that ... we've been doing some slightly different things ... They're going to come in time. You have a turnover drought, eventually they're going to end up coming, that's kind of where we were. We knew the sacks were going to come. We didn't have a shortage of hits and pressures on the quarterback in the first three or four weeks. We just weren't getting him down."

Well, they are now. The Rams have 16 sacks over the last four games from eight different players. Defensive end Robert Quinn has had six in the last four games, and Fisher said lining up Quinn and rookie defensive tackle Aaron Donald on the same side of the formation at times has provided a spark.

At the same time, Broncos quarterback Peyton Manning, with legendary anticipation and recognition skills, will always be difficult to sack no matter how the line in front of his is playing.

The Broncos have made two changes at right tackle, and a change at right guard and center over the last four games. They have had 36 rushing attempts go for no gain or negative yardage this season, and three of the sacks on Manning have come with three-man rushes.

"Their front has been active all season long, in my opinion," Manning said of the Rams. "Lots of first-round draft choices, guys who were great players in college and made the transition to the NFL and they're all impact players. [We've] got to be able to control those guys somehow. That falls on everybody, falls on the run game, falls on the receivers getting open on time, falls on me making quick decisions because it's an active bunch."

Defenses have found some success at times pounding away at the middle of the formation against the Broncos. Against the Oakland Raiders this past Sunday, Manning had four passes deflected at the line of scrimmage, had two interceptions and was forced into an intentional grounding penalty in the first half alone, at least before the Broncos got things dialed in with a flurry just before halftime to turn the game into a 24-point rout.

That was against a Raiders team that is currently last in the league in sacks with just eight -- the same number of sacks the Rams had against the Kansas City Chiefs two weeks ago.

"The challenge is still going to be to make them hold the ball," said Rams linebacker James Laurinaitis. "[Manning] gets rid of it. I don't care how fast Robert Quinn is, if [Manning] is getting rid of the ball in under two seconds, it doesn't matter how athletic your D-line is or how tough they are. It's not going to matter until we get there."