The Three Ageing Curves and The Disability Threshold
We all age. The question is not whether we age, but which ageing curve we follow.
Research identifies three potential life curves that describe how physical and mental capacity changes over time. These curves help explain why some people remain independent and active well into later life, while others experience earlier decline.
The Three Ageing Curves (or Potential Life Curves)
The research identifies three potential ageing curves, which are summarised as follows:
1. The Typical / Usual Life Curve
The Typical or Usual Life Curve shows a steep decline in the ageing process from around 35 years of age. This curve has often been described as resembling a steep ski slope.
People following this curve experience earlier and faster loss of strength, function and resilience than is necessary. This pattern represents the most common ageing trajectory in Australia.
2. The Pessimistic / Optimistic Life Curve
The Pessimistically/Optimistic Life Curve shows a lesser decline.
Individuals on this curve generally have a more optimistic approach to lifestyle and make some positive health choices. While decline still occurs, it happens more gradually than on the usual life curve.
3. The Successful Ageing Life Curve
The Successful Ageing Life Curve strives to maintain, as closely as possible, the physical and mental attributes of a 35-year-old until the end of life – where you ‘drop off life’s cliff’.
Clearly, some decline is inevitable. However, this model also includes the concept of compressed morbidity, where the period of illness or functional decline is shortened and occurs late in life rather than gradually over decades.
Sadly, you will note that your body begins to age at around 35 years.
This website encourages you to pursue your own successful ageing life curve and live the dream.
Remember: life is not a dress rehearsal.
The Disability Threshold
If someone is pursuing the usual life curve, there is a strong chance they will fall below the disability threshold, as shown in the diagram.
The hypothetical disability threshold is reached when a person can no longer look after their own daily needs and requires assistance to undertake normal functions.
While this level of decrepitude can often result from disease or cancer, it may also be the result of usual ageing alone.
Why the Disability Threshold matters
As we have seen, usual ageing is frequently the result of exposure to behavioural and biomedical risk factors. These can weaken immune response and increase vulnerability to infection, illness and functional decline.
One of the key problems with ageing is that many people believe disability and decrepitude are inevitable. This belief itself becomes a powerful risk factor.
An observation by Marilyn Ferguson is particularly relevant:
“Of all the self-fulfilling prophecies in our culture, the assumption that ageing means decline and poor health is probably the deadliest.”
By understanding these curves, and recognising the role lifestyle plays in determining which path we follow, we can begin to make informed choices about how we age.