The 32-year-old will lead New Zealand in today's test against the West Indies at the University Oval.
His back ''is a little bit stiff'' but ''it is all right'', he maintained yesterday. But, judging by the amount of stretching he does these days, it must still be of serious concern.
McCullum was forced to return home early from the recent tour of Bangladesh because of back pain and had time to think about his future. And not all of it was positive.
''Post Bangladesh, it has been pretty well reported since that I took some time to have a think about things,'' McCullum said when asked whether the injury threatened his playing future.
''[I] know that my test performances haven't been up to standard of late as well. I guess you couple that with a slight injury and you start to have some pretty dark thoughts.''
McCullum has played international cricket for the best part of 12 years and said it had taken a toll on his body.
He has had problems with his knees and back and gave up the gloves at test level to prolong his career.
Despite some doubts creeping in from time to time, McCullum remains committed and is eager to recapture his form.
He has not scored a test hundred in three years and was out of sorts in Bangladesh.
''I'm very determined to put the back aside and just get out there and perform for my team.
''When I took over this job [captaincy] I had some really big visions for this team ... and that certainly hasn't changed.
''Just because you are going through a few low scores or a few tough times doesn't mean you should change your goals. I'm still very determined to lead this team strongly from the front and it starts with performance obviously.''
