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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.

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a Schematic diagram of the experimental setup (backward perturbation position illustrated). Subjects stood supported at an angle of 15° to the vertical. The tether was released unexpectedly, inducing a balance perturbation. b Raw data from a typical backward balance recovery trial (dark gray area and black, dashed lines) and a fall trial (light grey area and gray, solid lines), showing left sternocleidomastoid EMG (SCL), anterior deltoid EMG (DAL), rectus femoris EMG (RFL), right tibialis anterior (TAR), lateral movement of the left elbow marker, and upward movement of the right foot marker. Tether release is at time = 0 ms
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Fig1: a Schematic diagram of the experimental setup (backward perturbation position illustrated). Subjects stood supported at an angle of 15° to the vertical. The tether was released unexpectedly, inducing a balance perturbation. b Raw data from a typical backward balance recovery trial (dark gray area and black, dashed lines) and a fall trial (light grey area and gray, solid lines), showing left sternocleidomastoid EMG (SCL), anterior deltoid EMG (DAL), rectus femoris EMG (RFL), right tibialis anterior (TAR), lateral movement of the left elbow marker, and upward movement of the right foot marker. Tether release is at time = 0 ms

Mentions: The participants stood barefoot on a wooden block (length × width × height: 60 × 38 × 30 cm) located flush with a gymnasium mattress (length × width × height: 480 × 240 × 30 cm). A tether was attached at one end to an electromagnetic brake (Warner Electric model PB500, South Beloit, IL) and at the other end to a chest harness worn by the participant (Fig. 1a). The participants placed their feet at a fixed position on the wooden block and the length of the tether was adjusted such that it supported the participant in a ∼15° backward or leftward-inclined position (by means of visual comparison of the lean angle with a reference line). For backward trials, the tether was attached to the front of the harness, whereas for leftward trials, it was attached to the right side of the harness. Postural perturbations were induced by sudden release of the tether (90% decay time in tether force = 15 ms).Fig. 1


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

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

a Schematic diagram of the experimental setup (backward perturbation position illustrated). Subjects stood supported at an angle of 15° to the vertical. The tether was released unexpectedly, inducing a balance perturbation. b Raw data from a typical backward balance recovery trial (dark gray area and black, dashed lines) and a fall trial (light grey area and gray, solid lines), showing left sternocleidomastoid EMG (SCL), anterior deltoid EMG (DAL), rectus femoris EMG (RFL), right tibialis anterior (TAR), lateral movement of the left elbow marker, and upward movement of the right foot marker. Tether release is at time = 0 ms
© Copyright Policy
Related In: Results  -  Collection

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

Fig1: a Schematic diagram of the experimental setup (backward perturbation position illustrated). Subjects stood supported at an angle of 15° to the vertical. The tether was released unexpectedly, inducing a balance perturbation. b Raw data from a typical backward balance recovery trial (dark gray area and black, dashed lines) and a fall trial (light grey area and gray, solid lines), showing left sternocleidomastoid EMG (SCL), anterior deltoid EMG (DAL), rectus femoris EMG (RFL), right tibialis anterior (TAR), lateral movement of the left elbow marker, and upward movement of the right foot marker. Tether release is at time = 0 ms
Mentions: The participants stood barefoot on a wooden block (length × width × height: 60 × 38 × 30 cm) located flush with a gymnasium mattress (length × width × height: 480 × 240 × 30 cm). A tether was attached at one end to an electromagnetic brake (Warner Electric model PB500, South Beloit, IL) and at the other end to a chest harness worn by the participant (Fig. 1a). The participants placed their feet at a fixed position on the wooden block and the length of the tether was adjusted such that it supported the participant in a ∼15° backward or leftward-inclined position (by means of visual comparison of the lean angle with a reference line). For backward trials, the tether was attached to the front of the harness, whereas for leftward trials, it was attached to the right side of the harness. Postural perturbations were induced by sudden release of the tether (90% decay time in tether force = 15 ms).Fig. 1

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