Not the story it first appears to be...
Y'r 'onor, my physical activity has been impaired and to provie this I will wear a device that will measure my activity during a period when I am aware that my activity is being measured, and the results of monitoring my activity during this period, as taken by this objective device, shall support my claim of impairment.
I promise not to alter my activity whilst wearing the device during the specified period in order to subjectively alter the results of the objective assessment.
It's not as if the data was collected at a time when the interested party was not aware and therefore not able to alter their behaviour to suit their claim.
It's a complete and utter non-story in that respect and highly unlikely to lead to such information being demanded in retrospect by a respondent in a case given that this establishes absolutely no precedent in respect of obtaining historical data from another party without their consent.