The monarch has faced ongoing “episodic mobility problems”, stretching back to last autumn, and now uses a walking stick.
Her royal physicians are also likely to be close at hand in case they are needed as the monarch, now just four years away from her 100th birthday, undertakes a busy run of appearances to mark her milestone reign.
In recent months, the 96-year-old Queen has cancelled a run of major engagements including the State Opening of Parliament.
But in the weeks leading up to her Jubilee celebrations, she has also made surprise visits to open the Elizabeth line and to tour, using a golf buggy, the Chelsea Flower Show.
She flew to Balmoral at the weekend, taking the opportunity to rest during a short break ahead of the high profile national events.
In October last year, she used a walking stick at a Westminster Abbey service – the first time she had done so at a major engagement.
A week later, after a busy autumn programme, she was ordered to rest by her doctors and advised to cancel a trip to Northern Ireland.
The Queen was secretly admitted to hospital for “preliminary investigations” and had her first overnight stay in hospital for eight years on October 20 last year.
The next day she was back at her desk at Windsor, carrying out light duties.
But concern for her health mounted when she pulled out of more high-profile engagements, including the COP26 climate change summit and the Festival of Remembrance, with Buckingham Palace saying she had been advised to continue to rest and to not carry out any official visits.
She was intent on attending the Remembrance Sunday service at the Cenotaph, but missed this due to a sprained back.
For more than three months she carried out only light duties, including virtual and face-to-face audiences in the confines of Windsor Castle.
In February, she celebrated her Platinum Jubilee, meeting charity workers at Sandringham House and cutting a Jubilee cake in what was her largest in-person public engagement since October.
Many of her duties are now carried out by video calls, and the country’s longest-reigning sovereign remarked during a in-person audience in February: “Well, as you can see, I can’t move.”
There were fears for her health when she finally caught Covid, testing positive on February 20.
The triple-vaccinated Queen suffered from mild cold-like symptoms, but said the virus left her “very tired and exhausted”.
She carried on with light duties while self-isolating at Windsor, but cancelled some virtual audiences.
She pulled out of the Commonwealth Day service at Westminster Abbey in March, a significant date in the royal calendar given the importance to her of the family of nations, and did not attend the Maundy Thursday service.
But she rallied to honour the Duke of Edinburgh at a memorial service at the end of March, walking slowly and carefully with the aid of a stick, and holding on to the Duke of York’s elbow for support.
In May 2022, she missed the State Opening of Parliament for the first time in nearly 60 years, with Buckingham Palace attributing her absence to “episodic mobility problems”.
The Prince of Wales and the Duke of Cambridge opened Parliament on her behalf as Counsellors of State, with Charles reading the Queen’s Speech for a historic first time.
Much has changed in the past seven months, with Buckingham Palace mostly only confirming the Queen’s attendance at engagements on the day, with the decision dependent on how she is feeling in the morning.
The Queen did go to the Windsor Horse Show last month and she was also the guest of honour at the equestrian extravaganza A Gallop Through History near Windsor, the first major event of the Jubilee festivities.
She also made a surprise appearance to officially open the Elizabeth line at Paddington Station, looking bright and cheery, but with her visit limited to just ten minutes.
The monarch also turned up at the Chelsea Flower Show, and was driven around the floral extravaganza in her new hi-tech golf buggy for her comfort.
The Platinum Jubilee is the first major milestone the Queen has celebrated without the Duke of Edinburgh, who was at her side during the ups and downs of her long reign.
Philip – the man the Queen described as her “strength and stay” – was married to the monarch for 73 years and devoted decades of his life to royal duty.
He died at the age of 99 in April last year during the pandemic, leaving the Queen grieving for her lifelong confidant.
Ed Sheeran is to perform his love song Perfect at the Jubilee Pageant in a moving tribute to the Queen and Philip.
At the finale of the carnival procession through the streets of London on Sunday, the star will sing the hit romantic ballad as footage of the couple fills the giant screens around the stage.
Other tributes to Philip will appear in the pageant, with a Bollywood-inspired interpretation of the Queen and the duke’s wedding day.
A 6m wedding cake, housing a sound system playing classic Bollywood anthems and accompanied by 250 Bollywood dancers, will process down The Mall in a reimagining of their 1947 marriage celebration.
A representation of Philip’s beloved sailing boat Bluebottle will feature in the section devoted to the “Queen’s Favourites”, which will also include puppet corgis and horses.
In her most recent Christmas Day broadcast, the Queen poignantly reflected on a year of personal grief, saying there was “one familiar laugh missing” as she acknowledged the death of her husband.