But with music also being her career, she had to continue playing through the pain, initially thinking she "just needed to toughen up". Then she met Dunedin man Rowan Ellis whom she now says she owes her life to.
In 2010, Dr du Plessis moved from South Africa to Dunedin for a job at the University of Otago where she is a senior lecturer in cello and pedagogy of music performance.
Shortly after, she had to return to play a concerto with an orchestra in Cape Town, a performance which was both a privilege and a huge occasion, she said.
A combination of factors, which she believed included the stress of the move to New Zealand and reacting to the cold, she developed shoulder pain.
But she could not stop practising — the story of most musicians who earned their money from playing. Her job depended on those international performances and, as a passionate musician, she also wanted to play, so she practised through the pain.
Returning from South Africa, she spoke to "every single person that musicians usually go to" including physiotherapists, acupuncturists, massage therapists and sports specialists, and regularly did shoulder exercises.
Then her back began to hurt. It got increasingly worse and she discovered she had ripped two discs in her lower back. She was virtually unable to move for about eight weeks.
She was in "absolute agony" and on heavy medication, including morphine. MRI scans did not show what was going on, she said.
She spent about three and a-half years in severe pain before having to return to South Africa to record a CD. By then, she could not lift her elbows and she was getting pins and needles in her fingers — "not so ideal for a musician".
She spoke to the South African Olympic team’s sports physician who told her she had to stop playing her instrument. Telling her she was moving incorrectly and using the wrong muscles, he encouraged her to move to South Africa for three months for treatment.
Unable to commit to that, Dr du Plessis got in touch with Mr Ellis in Dunedin, having heard that he taught people how to move correctly. He listened to her story and told her the pain was because of a lack of awareness and control of her muscles.
Using electromyography on her, which showed the tension in her trapezius muscle and lower back, he said he could literally see her pain.
Dr du Plessis said he could immediately see when she breathed, lifted her arms or toes, or did any action. She would lever first off her trapezius and lower back; she did not have awareness of other muscles.
While people talked about movement in music, hardly anyone talked about muscles, she said.
Within three months of working with EMG, coupled with explanations, exercise and education, she had no pain and was off medication. For another three months to a year, she had lapses when she would still get pain, but she knew what to do to relieve that.
"I had the power and confidence to know exactly what to do ... having that power back changed my life," she said.
Since then, Dr du Plessis has researched the topic and is now writing a book. She has also been teaching cellists — and helping other people, including hairdressers — about improving their muscle and movement habits, training their mind to move correctly.
"My research showed most people have a different perception of what they are doing from what they are really doing. That was my case ... I didn’t have awareness.
"It’s possible for muscles to cause havoc. I thought I had an incredible disease, [it was] caused by muscle and movement habits.
"I would never have been able to know what was going on if I didn’t see it with my own eyes."
