I often mention that qigong is a very mindful practice because it helps to keep you focussed in the moment. Ad that is a very important aspect of mindfulness. But an equally important aspect of mindfulness is being non judgmental.
Being non judgemental means you don't beat yourself up about how things are, So much stress is caused by our own critical judgments on ourselves and our actions. Being mindful of that tendency, noticing when you are being judgmental and recognising that it is a very unhelpful trait are key benefits of mindfulness.
Sometimes this means accepting that in this moment you have this pain, this level of energy, that this is all you can do. It means accepting your ,limitations . 'But surely that means you will never improve?' I here you say. Not so. If you have a clear goal (eg to improve your practice of qigong) being no judgmental on the days when you know your practice falls short of what you would wish is important. Becasue I often say it isn't about doing the moves perfectly...but doing them perfectly for you. Not judging yourself critically because you are not holding perfect stance, or not practicing it for as long as you would wish each....or even not practicing it each day because...you know life happens.
When you know what you SHOULD be doing (in an ideal world, or if you were monk on a mountain top in Tibet who did nothing except practice qigong 10 hours a day) then that improves the benefit of what you physically CAN do,
I run sessions for wheelchair bound people who have very limited movement. I always tell them 'doing it in your imagination is fine ' They will NEVER be able to physically get the stances and moves perfect. But if they can breath and use their imagination they still get huge benefits.
I realised to day that applies to equally to me. I need to be non judgmental on the days when my stance isn't good, when I can't hold my core abdominal muscles engaged, when I run out of time or energy to do even minimal practice. That doesn't mean I can be complacent. I know what I WANT to be doing.. And I can assure you my practice has improved immeasurably since the first time I was introduced to shibashi.
Accepting your limitations as long as you have a real desire to improve is mindfulness in action.