should work here

... erschwerte Gangprüfungen waren schon damals nicht mehr möglich.
... more difficult/involved gait tests were already no longer possible at that time .

This is, what I think may be meant.

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Note added at 1 hr (2009-03-10 17:46:06 GMT)
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Qualitative measures may not differentiate severity of deficits after an acute or subacute stroke. The aim of this study was to contrast the utility of performance-based gait tests with qualitative measures in a sample of acute stroke patients. DESIGN: Twenty acute stroke subjects had their performance-based gait measured by gait speed, walking distance, gait energy expenditure, and gait energy cost. They were also qualitatively evaluated for cognition, functional outcomes, motor impairment, and Functional Ambulation Category. RESULTS: Strong and significant correlations were observed among performance-based gait tests. Qualitative scales indicated moderate to minimal deficits in each domain evaluated, although they were not correlated among themselves, except for Functional Ambulation Category and FIM and FIM and Mini-Mental State Exam. Functional Ambulation Category correlated with performance-based gait tests. CONCLUSIONS: Performance-based gait tests are feasible to conduct during early recovery after a stroke and allow better discrimination among the patients than qualitative measures.
www.biomedexperts.com/Abstract.bme/12394997/Performance_bas...

To bring out abnormalities in gait and balance, ask the patient to do more difficult maneuvers;
http://www.neuroexam.com/content.php?p=38;

Complex gait analysis in diabetic neuropathy
http://www.dh.gov.uk/en/Researchanddevelopment/A-Z/Physicala...



Course Content:
The course aims to provide participants with practical knowledge and guidelines for the application of gait analysis methods in a clinical context. Principles of biomechanics will be covered to provide participants with a working knowledge of human gait and how to describe it; and simple and complex gait analysis techniques and instrumentation will also be reviewed.
http://www.strath.ac.uk/media/departments/prosthetics/Short ...



Ankle spasticity and complex gait analysis including kinematic electromyography (EMG) of the soleus and tibialis muscles were assessed before treatment and ...
http://tinyurl.com/dlu6wc

I think I would use 'advanced' rather than 'complex'or 'difficult', because it indicates the higher levels of mobility skills that the patient can no longer handle.