Jen, aged 67, enjoys an active retirement. A former health professional, she focuses on improving her health as she ages, and is physically active — hiking, gardening and swimming. Jen has a background of Graves’ disease, in remission for 10 years.

She is a lifelong non-smoker who takes no medications. She consumes a wholefood low carbohydrate diet.

For the past few years, one of her great pleasures is a weekly bushwalk, often combined with a cold water dip during the cooler months.

Jen is perplexed when, five days after a day procedure that required a short general anaesthetic, she develops widespread aches and pains, similar to her previous experiences of post-exercise delayed onset muscle soreness. This is odd as she has not done anything sufficiently vigorous to account for this.