Geoffrey Walker, then aged in his late 50s, was enrolled in the Canberra Institute of Technology in 2006 when the injury occurred during a class exercise.

The routine, designed by a fellow student, involved "jumping squats" – bending the knees then leaping off the floor – repeated over 30 seconds.

Mr Walker suffered a painful, crunching feeling in his left knee after five or six jumps, but continued to do them.

Medical experts later agreed that the jumping squats tore cartilage in his knee, causing ongoing pain and, over time, disability.

His win in the ACT Supreme Court last week was his second payout related to that knee, after he injured it in 2007 when he fell in a Bunnings store.

He settled that case in December last year for $75,000 plus costs.

Mr Walker, a former fitter and turner, had enrolled in the certificate III fitness course aged 56 and feeling fitter "than he had been at age 30".

Chief Justice Terrence Higgins noted he "was, clearly, very fit for his age. Indeed, he could even do 'the splits'."

Mr Walker's doctor cleared him to undertake the course but warned him against overexertion.

The compensation claim hinged on the type of squat involved.

Mr Walker said he was asked to perform a "deep-knee bend" – a low squat in which the knees bend more than 90 degrees – between jumps.

He later cited a course textbook, which warned that the exercise was unsafe.

However, the teacher who oversaw the lesson, Julian Everett, said the students were performing "partial squats", a less dangerous exercise.

The CIT also pointed out that Mr Walker had signed a disclaimer noting it was not liable for personal injuries arising from class activities.

However, Chief Justice Higgins said such disclaimers could not be used to deny the right to damages.

He also said the CIT's instructors "had a duty to the students to ensure that any exercise to be prescribed by another student ... was not attended by undue risk or executed in an unsafe manner".

"The repetition of deep-knee bends is, I am satisfied, an unsafe practice."

Mr Walker finished the course and obtained a job at Flames Fitness but, due to his knee injury, "he could not move quickly enough to meet the employer's expectations".

The court noted he would now need a left knee replacement.

The knee's weakness had also contributed to injuries to his right knee, which he had already replaced.

Chief Justice Higgins found it was unrealistic to assume Mr Walker's qualification would have boosted his pre-existing income, as most personal trainers worked part time and made little money.

Mr Walker had managed to continue paid work as a life model, handy man and cleaner, but his knee continued to make physical work difficult.

The judge awarded him $150,000 in general damages, about $33,000 in expenses, and about $72,000 for past and future income loss.

He is yet to decide on legal costs.