PubMed · 11275874
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M Harrahill. 2001. Falls in the elderly: making the difference.. https://doi.org/10.1067/men.2001.113195
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The objective of this study was to investigate the modulation of the ankle muscle electromyographic (EMG) response as a function of mental set. Thirteen young healthy subjects underwent 40 unexpected and self-initiated drops from 30 cm above two separate force-plates. Following unexpected drops, reflex activities were observed in the medial gastrocnemius (MG) and tibialis anterior (TA) at mean latencies (+/- SD) of 83.59 +/- 10.1 and 99.43 +/- 21.82 ms, respectively. Following self-initiated drops, the response latency of the MG was significantly shortened (to 71.98 +/- 10 ms, P<0.05), and the TA was significantly lengthened (to 183.33 +/- 45 ms, P<0.05) when compared with unexpected drops. Such a modulation was associated with a significant reduction of the impact force on landing as compared with unexpected drops (by 17%, P<0.05). Interestingly, a negative correlation was found between the onset of the TA EMG response and the magnitude of the impact force on landing during expected (r= -0.66, P<0.05) but not unexpected drops.
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This study investigated the influence of fear of falling or postural threat on the control of posture and movement during a voluntary rise to toes task for 12 healthy young adults. Postural threat was modified through alterations to the surface height at which individuals stood (low or high platform) and changes in step restriction (away from or at the edge of the platform) creating four levels of postural threat: LOW AWAY, LOW EDGE, HIGH AWAY and HIGH EDGE. To rise to the toes, an initial postural adjustment must destabilise the body so that it can be moved forward and elevated to a new position of support over the toes. Centre of pressure and centre of mass profiles, as well as tibialis anterior (TA), soleus (SO) and gastrocnemius (GA) muscle activity patterns were used to describe this behaviour. The results showed that the performance of the rise to toes task was significantly modified when positioned at the edge of the high platform. In this situation, the central nervous system reduced the magnitude and rate of the postural adjustments and subsequent voluntary movement. Although the duration of the movement was lengthened for this most threatening condition, the sequencing and relative timing of TA, SO and GA muscle activity was preserved. These changes in rise to toes behaviour were accompanied by evidence of increased physiological arousal and participant reports of decreased confidence, increased anxiety and decreased stability. Evidence of fear of falling effects on anticipatory postural control is clinically relevant as it may explain deficits in this control observed in individuals with balance disorders. For example, individuals with Parkinson's disease or cerebellar dysfunction demonstrate impaired performance on the rise to toes task as reflected in alterations of both the timing and magnitude of their anticipatory postural adjustments. Our findings suggest alterations in the magnitude of postural adjustments may be magnified by fear of falling while changes in the timing of postural adjustments may reflect underlying pathology.