It’s been a recurring trend over the past few years. Red Sox starting pitchers don’t go deep enough into games, the bullpen has to carry a bigger load, and as the weeks and months go on the strain gets heavier until the staff eventually runs out of steam.

Typically the collapse hasn’t happened until the second half, but now the Red Sox bullpen is already showing dangerous signs of overuse.

Between frequent short outings by starters and the club’s league-high 12 extra-inning games, the Red Sox have leaned heavily on their relievers, especially over the last month. Even with a favorable schedule and more frequent off-days, the club has struggled to reset and has now gone long stretches where multiple relievers are either unavailable or have been pressed into action on short rest any given night.

That workload is already having a noticeable impact on the field, and Red Sox manager Alex Cora acknowledged Tuesday that it’s a concern.

“It seems like we’ve been in this stretch where everybody pitches every day for a month now,” Cora said.

Entering Tuesday night’s game against Tampa Bay, the Red Sox ranked fifth in MLB in innings pitched by relievers with 261.1, and the club is one of only four that has at least three pitchers who have already appeared in at least 30 games this season — those being Brennan Bernardino (31), Greg Weissert (31) and Aroldis Chapman (30).

But the real problem has been the accumulation of innings recently.

Earlier this season the Red Sox had a stretch of 16 consecutive games where the starting pitcher went at least five innings, but since that stretch ended on May 6 all Red Sox starters outside of Garrett Crochet have collectively averaged 4.1 innings per start.

That includes five outings where the starter didn’t pitch into the fourth inning, three of which came in a four-game span between June 2-6.

“It’s just the real short ones that have put us in a bad spot,” Cora said.

Meanwhile, since May 6 Red Sox relievers have collectively made the most appearances of any club in MLB (120), and nobody in baseball has appeared in more games than Bernardino (19) and Chapman (17), with Weissert (16) among seven players tied for third.

Bernardino has clearly suffered under the heavy workload. The left-hander allowed just one earned run in 16 outings in the month of May, but since the start of June has now allowed six runs over seven innings in his last four appearances, including at least one each time out.

The Red Sox are also without several arms who were expected to be key contributors. Top set-up man Justin Slaten is on the IL with right shoulder inflammation, and veteran Liam Hendriks — originally expected to be a candidate for the closer job — has spent two stints on the IL and has been ineffective when available.

The Red Sox bullpen has held up as well as can be reasonably expected. Even with so many innings the group ranks 12th in bullpen ERA (3.58) and has actually been better recently (3.03, 6th in MLB since May 6). But if the club keeps leaning so hard on Bernardino, Weissert and the 37-year-old veteran duo of Chapman and Justin Wilson (27 games), the team will be asking for trouble.

“You start looking at what we’ve done bullpen-wise over the last month, we’ve been throwing the ball great,” Cora said. “It’s just usage now, some guys are feeling it.”

For Cora the solution is simple. The starting pitchers need to do their jobs.

“To start winning consistently you’ve got to pitch better in the first five innings of games, you have to, and give the offense a chance to do their thing and get the lead,” Cora said. “From there it takes stress out of everybody.”

Slaten makes progress

Earlier this month the Red Sox lost Slaten to the 10-day injured list with right shoulder inflammation, and the way Cora told it on Tuesday, it doesn’t sound like he’ll be coming back anytime soon.

“It’s slower than we expected, let’s put it that way,” Cora said. “He hasn’t reacted to treatment the way we expected so this is kind of a slow process now.”

Slaten has been one of Boston’s most important relievers, posting a 3.47 ERA over 23.1 innings. Prior to going on the IL on June 1, the right-hander had made 18 of his 24 appearances in the eighth inning or later, and all but two of his outings have come with the Red Sox tied or with a lead.

The 27-year-old also served as the bridge to Chapman, and without him the club has been forced to lean even more heavily on arms like Weissert, Wilson and Bernardino.

“Obviously it’s a big loss just like last year when we lost him and Chris (Martin),” Cora said. “Hopefully this is just something we can figure out in the upcoming days and we can get him going, but right now it doesn’t seem like it’s going to be soon.”

Extra innings

Outfielder Wilyer Abreu (left oblique strain) is expected to start swinging on Friday, and if he can then the expectation is he’ll be ready to return as soon as he’s eligible ahead of the upcoming series in San Francisco starting June 20. … Right-handers Tanner Houck (right flexor pronator strain) and Nick Burdi (right foot contusion) threw bullpens on Tuesday. Houck is expected to throw another over the weekend and Burdi could begin a rehab assignment by the end of the week. … Left-hander Chris Murphy (Tommy John rehab) was promoted to Triple-A as part of his ongoing rehab process. Murphy has made five appearances in the minors, twice at High-A Greenville and three times at Double-A Portland, but Cora said over the weekend he anticipates Murphy will need a full spring-training’s worth of ramp up before he’s ready to return to the big league club.