Limits...
Automated postural responses are modified in a functional manner by instruction.

Weerdesteyn V, Laing AC, Robinovitch SN - Exp Brain Res (2008)

Bottom Line: The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses.It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task.However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

View Article: PubMed Central - PubMed

Affiliation: Department of Rehabilitation, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands. v.weerdesteyn@reval.umcn.nl

ABSTRACT
The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses. Although these responses occur before voluntary control comes into play, previous research has shown that they can be functionally modulated on the basis of cognitive set (experience, advanced warning, instruction, etc.). It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task. In the present study, the effects of instruction on automated postural responses in neck, trunk, shoulder, and leg muscles were investigated when people were either instructed to recover balance after being released from an inclined standing posture [balance recovery (BR) trials], or not to recover at all and fall onto a safety mattress in the most comfortable way [fall (F) trials], in both backward and leftward directions. Participants were highly successful in following the instructions, consistently exhibiting stepping responses for balance recovery in BR trials, and suppressing stepping in the F trials. Yet EMG recordings revealed similar postural responses with onset latencies between 70 and 130 ms in both BR and F trials, with slightly delayed responses in F trials. In contrast, very pronounced and early differences were observed between BR and F trials in response amplitudes, which were generally much higher in BR than in F trials, but with clear differentiation between muscles and perturbation directions. These results indicate that a balance perturbation always elicits a postural response, irrespective of the task demands. However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

Show MeSH
Average changes in flexion and abduction angles (±SE) of the left (L) and right (R) arm between tether release and 200 ms post-release for balance recovery (diamonds) and fall trials (squares). * P < 0.05
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2279151&req=5

Fig4: Average changes in flexion and abduction angles (±SE) of the left (L) and right (R) arm between tether release and 200 ms post-release for balance recovery (diamonds) and fall trials (squares). * P < 0.05

Mentions: Hence, many of the muscles recorded showed significantly higher EMG amplitudes in BR than in F trials, with the earliest and most consistent differences between instructions being present in sternocleidomastoid. However, instruction-related differences in rectus abdominis were only present in leftward perturbations. Furthermore, in both perturbation directions, EMG amplitude in rectus femoris of the stance limb was greater in BR than F trials. Finally, instruction had differential effects on shoulder muscle EMG amplitudes for the two perturbation directions. Analysis of shoulder kinematics revealed that the differential effects of instruction on EMG amplitudes also resulted in corresponding changes in shoulder abduction and flexion angles within 200 ms after tether release (Fig. 4). In backward trials, the deltoids (shoulder abductor muscles) showed higher activity in BR than F trials. This corresponded to increases in shoulder abduction angles in BR trials that were more than twice as large compared to F trials (left: 10.7° vs. 4.7°, SE of the difference 2.1°, P = 0.018; right: 8.0° vs. 3.5°, SE of the difference 1.5°, P = 0.014, Fig. 4a).Fig. 4


Automated postural responses are modified in a functional manner by instruction.

Weerdesteyn V, Laing AC, Robinovitch SN - Exp Brain Res (2008)

Average changes in flexion and abduction angles (±SE) of the left (L) and right (R) arm between tether release and 200 ms post-release for balance recovery (diamonds) and fall trials (squares). * P < 0.05
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2279151&req=5

Fig4: Average changes in flexion and abduction angles (±SE) of the left (L) and right (R) arm between tether release and 200 ms post-release for balance recovery (diamonds) and fall trials (squares). * P < 0.05
Mentions: Hence, many of the muscles recorded showed significantly higher EMG amplitudes in BR than in F trials, with the earliest and most consistent differences between instructions being present in sternocleidomastoid. However, instruction-related differences in rectus abdominis were only present in leftward perturbations. Furthermore, in both perturbation directions, EMG amplitude in rectus femoris of the stance limb was greater in BR than F trials. Finally, instruction had differential effects on shoulder muscle EMG amplitudes for the two perturbation directions. Analysis of shoulder kinematics revealed that the differential effects of instruction on EMG amplitudes also resulted in corresponding changes in shoulder abduction and flexion angles within 200 ms after tether release (Fig. 4). In backward trials, the deltoids (shoulder abductor muscles) showed higher activity in BR than F trials. This corresponded to increases in shoulder abduction angles in BR trials that were more than twice as large compared to F trials (left: 10.7° vs. 4.7°, SE of the difference 2.1°, P = 0.018; right: 8.0° vs. 3.5°, SE of the difference 1.5°, P = 0.014, Fig. 4a).Fig. 4

Bottom Line: The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses.It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task.However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

View Article: PubMed Central - PubMed

Affiliation: Department of Rehabilitation, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands. v.weerdesteyn@reval.umcn.nl

ABSTRACT
The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses. Although these responses occur before voluntary control comes into play, previous research has shown that they can be functionally modulated on the basis of cognitive set (experience, advanced warning, instruction, etc.). It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task. In the present study, the effects of instruction on automated postural responses in neck, trunk, shoulder, and leg muscles were investigated when people were either instructed to recover balance after being released from an inclined standing posture [balance recovery (BR) trials], or not to recover at all and fall onto a safety mattress in the most comfortable way [fall (F) trials], in both backward and leftward directions. Participants were highly successful in following the instructions, consistently exhibiting stepping responses for balance recovery in BR trials, and suppressing stepping in the F trials. Yet EMG recordings revealed similar postural responses with onset latencies between 70 and 130 ms in both BR and F trials, with slightly delayed responses in F trials. In contrast, very pronounced and early differences were observed between BR and F trials in response amplitudes, which were generally much higher in BR than in F trials, but with clear differentiation between muscles and perturbation directions. These results indicate that a balance perturbation always elicits a postural response, irrespective of the task demands. However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

Show MeSH