The 34-year-forward might have looked as indestructible as ever last season as he anchored Edinburgh's unexpected run to the semi-finals of the Heineken Cup and put in the typically stalwart shifts for Scotland that brought his cap count up to 64, but the cracks were starting to show towards the end of that ferocious campaign and Jacobsen was omitted from the Scotland squad that toured Australia and the South Pacific in order to get his body back in shape.
The elbow injury he had picked up in a club match in January – and which had seriously restricted his training thereafter – was sorted out with an operation.
The shoulder problem he had carried for even longer was simply given time to rest. "That one is just an old man thing," he explained.
Yet while Jacobsen was taking things easy, Glasgow prop Ryan Grant moved stealthily into the Scotland loosehead slot and performed with distinction in all three Tests of Scotland's unbeaten summer tour and when he clocked in for pre-season training at Edinburgh, he was met by the substantial figure of John Yapp, the former Cardiff prop who had been signed by coach Michael Bradley to bolster the club's front-row resources.
Things like these can leave a fellow feeling uncomfortable, but as Jacobsen occupies a position on the field where discomfort is part of the job, he can just about cope.
Indeed, far from seeing a threat in the arrival of Yapp, who has started three of Edinburgh's four RaboDirect PRO12 games this season, Jacobsen prefers to dwell on the opportunity that the Welshman's arrival presents.
"Having these guys [South African prop Willem Nel also has joined Edinburgh recently] here takes pressure off you because you're not playing all the time," Jacobsen explained. "It's good in that way but in the past I've always played my best when I'm playing all the time. I have to work out a way of getting to my best with not so much game time.
"I hope to use the weeks when I'm not playing to train hard. Last year, I was playing pretty much 80 minutes every week. I didn't have time for extra training because I was always just getting ready for the next game. As the season went on, I started struggling with my extra gym and fitness stuff. I didn't feel I could do it. Now, I'll have time to do extra stuff."
It is understood that the coaches of Edinburgh and Glasgow have agreed an informal arrangement whereby top international players are not required to play more than five consecutive games. The absence of Greig Laidlaw and Ross Ford from the Edinburgh side which takes on Newport Gwent Dragons at Rodney Parade this evening can be explained by that policy.
Laidlaw's fly-half place is taken by Harry Leonard – although full-back Greig Tonks may move up to the playmaker's berth at some point – while Ford's shirt is worn by Andy Titterrell.
Bradley rarely had the luxury of being able to rotate players last season, and he is convinced that Jacobsen and Geoff Cross, his fellow inter-national prop, will feel the benefit as the season unfolds.
Bradley said: "Allan and Geoff are in a good position this year because we can spread the load. They had to carry everything last year. We're in a much stronger position now, which enables Allan to give more to a performance when he's starting. He's looking forward to it. He's been buzzing in training, which is great to see."
Of course, Bradley is also enjoying the internal competition that has been created in his strengthened squad. Against Cardiff Blues, Yapp and Nel, who had come on as replacements a little earlier, engineered a penalty try at a scrum. A week later, Jacobsen and Cross were determined to claim one of their own when the roles were reversed against Zebre.They duly got their try. "One of the funniest things I've seen in rugby," said Bradley with a smile.
Jacobsen has learned to accept that the Edinburgh system has changed. "I would have hoped for more game time but this is what we're doing at Edinburgh and it seems to be going okay," he said. "I would like this to be the start of a run, but I don't know what's happening. I just come into the meeting every Monday hoping I'm playing, like everyone else."