LONDON • Adele cancelled the remaining two shows of a sold-out residency at Wembley Stadium in June, after her doctor told her she had damaged her vocal cords.
Though only 29, the most powerful young voice in the music business had been here before. In 2011, she had suffered a haemorrhage to her vocal cords after singing live on a French radio programme. To repair the injury, she underwent a delicate, high-risk medical intervention: vocal cord microsurgery.
Other singers Meghan Trainor and Sam Smith also underwent career-saving surgery in their 20s. Vocal burnout is afflicting amateurs too. One veteran teacher in Italy said that female students in their early 20s who want to sing like Adele or young Whitney Houston are the ones who damage their vocal cords.
The rise in vocal injuries is linked to a change in what people consider good singing. Across all genres, it has become normal to believe that louder is better.
As a result, singers are pushing their cords like never before, which leads to vocal breakdown.
Voice coach Marianna Brilla said: "It's a motor problem. The singer has to understand it's the way you're running your engine" - the singing techniques. "If you don't fix the engine, it's going to happen again."
On Feb 12, 2012, three months after her surgery, Adele swept up six Grammys and thanked her surgeon, Dr Steven Zeitels, for restoring her voice.
In the years since, his business has boomed, along with those of many of his peers. In addition to his work on Adele, Dr Zeitels, who directs the Massachusetts General Hospital Centre for Laryngeal Surgery and Voice Rehabilitation, has repaired the cords of more than 700 performing artists, including Smith, Bono and Cher.
While the media was celebrating Adele's 2011 surgery, one woman in the music industry raised a dissenting voice. According to Ms Lisa Paglin, a former opera singer- turned-voice coach, Dr Zeitels had simply found a temporary fix. In the not too distant future, Adele would once again be forced off the stage.
It was a prediction that Ms Paglin and Ms Brilla, her coaching partner, were willing to stake their reputations on.
When Adele cancelled the final nights of her recent tour, they felt saddened but vindicated.
After years of research in musical archives, early scientific journals and the classroom, they say they can deliver what medical science has failed to: a permanent fix for vocal burnout.
Their solution requires the revival of an all-but-vanished singing method that is not just beautiful to the ear, but also easy on the throat. It is based on a provocative theory that has been gaining ground among a small cadre of international talents: People have all been singing wrong - even Adele.
Singing is a rough business. Every vocal performance involves hundreds of thousands of micro-collisions in the throat. The vocal cords are a pair of thin, reed-like, muscular strips located in the larynx, or voice box, in the throat.
When we are silent, the cords remain apart to facilitate breathing. When we sing or speak, air is pushed up from the lungs and the edges of the cords come together in a rapid chopping motion. By the time a soprano hits those lush high notes, her vocal cords are thwacking together 1,000 times a second.
Over years of heavy use, nodules or cysts form on the vocal folds, distorting the sound they create.
Singing through the wear and tear can cause the lesions to burst and bleed, creating voice-ruining scars, which is what happened to Adele in 2011.
Ms Brilla met Ms Paglin while studying voice at Indiana University's school of music. The two bonded over their love of Italian opera and their frustration with the way singing was taught, even by their legendary teacher Margaret Harshaw.
In 1977, Ms Brilla won a prestigious Fulbright scholarship to travel to Italy to search for a way to sing beautifully without risking injury. There, she heard glimpses of perfect arias from older, mostly Italian opera singers who learnt their craft in the early 20th century. These singers seemed to effortlessly produce clear, powerful musical tones, and many of them were performing well into their 60s, 70s and 80s.
Ms Paglin soon joined Ms Brilla in Rome, where they started spending hours each day at the national sound archive, La Discoteca di Stato, listening to early recordings.
Their research pointed them to a surprising conclusion: that responsibility for the modern decline of the voice lay at the feet of Verdi, Wagner and Puccini.
These three composers were the pop music sensations of their day. Music scholars credit them with being the first to challenge their singers to push their voices to new limits to capture the emotional ups and downs their characters were feeling.
But Ms Brilla and Ms Paglin heard something different - that the full-throated style Verdi and Wagner made popular in the late 19th century had subsequently infiltrated all singing genres.
In 1983, Ms Brilla convinced Maria Carbone, a retired Italian operatic soprano, to work with them. Carbone was nearing 80, but still had a powerful voice.
While she sang, Ms Brilla would clasp her abdomen to feel what was happening inside her body. "I could feel this tick, tick," she recalled. It was the natural up-down release of her diaphragm. "Nothing else was happening."
Carbone's ribcage was not ballooning out as she sang and there were no deep gulps of air, as is common with today's big-voiced singers. More amazingly, the movement of Carbone's abdomen while singing was just as quiet and rhythmic as when she spoke.
"It was a discovery of what the perfect singer's posture should be," Ms Paglin said.
Ms Brilla and Ms Paglin's track record with difficult cases has earned them a small international following.
Veteran Italian stage actor Moni Ovadia was one of their earliest big-name success stories. Throughout his mid-40s, he performed up to 250 shows a year, but, by 48, he was ready to quit show business. His voice had become flat and raspy and he found it physically painful to perform.
He credits Ms Paglin and Ms Brilla with restoring his voice and his career. "They saved my life," he said. Today, at 71, he can perform non-stop for up to three hours.