I have been thinking about T's observations about running and cycling, and my own conclusion that it is essential to find a form of exercise that is comfortable and around which one can build a routine and a narrative for one's own exercise.
Cycling fulfils all those criteria for T, and that is great.
But I think T must also return to running. Let me explain my argument.
The problem is, I think, that what happens as we become unfit is that we lose control over our own body weight. As this happens, everything becomes more of an effort - standing up, sitting down, walking - and we feel more tired doing more and more mundane things. Age compounds the problem by introducing creaking joints. Brilliant.
Unless we counter this (seemingly inevitable) process, and regain control then we will never feel really fit ever again.
Logically, to counter one force you must resist with an equal force. The only way to regain control over one's own bodyweight is to control the weight of one's own body when exercising.
Running, yoga, or any exercise where your weight is unsupported and you are moving (like press ups), is essential to providing that challenge. When overweight, these are all unpleasant (believe me I know!).
Therefore, cycling can continue to form the basis of a fitness routine, but it will not do enough to counter the loss of control over one's own body weight, essentially because the bike helps you out. It is an excellent addition (or foundation) to fitness, but we all need to find at least 3 hours a week to challenge ourselves properly.
If T were a client, I would encourage a narrative that included running, however displeasing the prospect, balance work on the swiss ball, and yoga.
And if it's any consolation, I'll be doing exactly the same thing myself.