### Abstract

Postural steadiness (sway) is used to evaluate the dynamics of the postural control system associated with maintenance of balance during standing. Recently, the chaotic behavior of many biomechanical systems has been examined using Lyapunov exponents, fractal dimension or attractor plot (reconstructed phase portrait). The purpose of this study was to investigate the effects of physical workload on postural stability during load holding task by measuring sway of center of pressure (COP). The experimental variables were weight of load (10 kg, 15 kg, and 20 kg) and height of holding a load (50 cm, 70 cm, and 90 cm). Ten male subjects participated in a repeated measures experiment in which 9 lifts were performed. The time of holding a load was for 10 sec. The sampling interval was 1 msec. The basic measures of postural stability (mean distance of the COP, mean velocity of the COP, and sway area) and the chaotic measures (fractal dimension and first Lyapunov exponent) of the COP were calculated. When the holding height increased, the mean velocity of the COP tended to increase but the first Lyapunov exponent of the COP decreased. On the other hand, the fractal dimension of the COP decreased with the increase in load weight. From the above results, it was clarified that physical workloads (load weight and holding height) affect the chaotic measures of the COP. It was implied that the physical workload can be measured by the chaotic features of the COP.

Original language | English |
---|---|

Pages (from-to) | 2553-2559 |

Number of pages | 7 |

Journal | Nihon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C |

Volume | 75 |

Issue number | 757 |

Publication status | Published - Sep 2009 |

Externally published | Yes |

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### Keywords

- Body sway
- Chaotic analysis
- First Lyapunov exponent
- Fractal dimension
- Holding task

### ASJC Scopus subject areas

- Mechanical Engineering
- Mechanics of Materials
- Industrial and Manufacturing Engineering

### Cite this

**Effects of physical workload on postural sway during load holding task.** / Iwase, Hirokazu; Murata, Atsuo.

Research output: Contribution to journal › Article

*Nihon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C*, vol. 75, no. 757, pp. 2553-2559.

}

TY - JOUR

T1 - Effects of physical workload on postural sway during load holding task

AU - Iwase, Hirokazu

AU - Murata, Atsuo

PY - 2009/9

Y1 - 2009/9

N2 - Postural steadiness (sway) is used to evaluate the dynamics of the postural control system associated with maintenance of balance during standing. Recently, the chaotic behavior of many biomechanical systems has been examined using Lyapunov exponents, fractal dimension or attractor plot (reconstructed phase portrait). The purpose of this study was to investigate the effects of physical workload on postural stability during load holding task by measuring sway of center of pressure (COP). The experimental variables were weight of load (10 kg, 15 kg, and 20 kg) and height of holding a load (50 cm, 70 cm, and 90 cm). Ten male subjects participated in a repeated measures experiment in which 9 lifts were performed. The time of holding a load was for 10 sec. The sampling interval was 1 msec. The basic measures of postural stability (mean distance of the COP, mean velocity of the COP, and sway area) and the chaotic measures (fractal dimension and first Lyapunov exponent) of the COP were calculated. When the holding height increased, the mean velocity of the COP tended to increase but the first Lyapunov exponent of the COP decreased. On the other hand, the fractal dimension of the COP decreased with the increase in load weight. From the above results, it was clarified that physical workloads (load weight and holding height) affect the chaotic measures of the COP. It was implied that the physical workload can be measured by the chaotic features of the COP.

AB - Postural steadiness (sway) is used to evaluate the dynamics of the postural control system associated with maintenance of balance during standing. Recently, the chaotic behavior of many biomechanical systems has been examined using Lyapunov exponents, fractal dimension or attractor plot (reconstructed phase portrait). The purpose of this study was to investigate the effects of physical workload on postural stability during load holding task by measuring sway of center of pressure (COP). The experimental variables were weight of load (10 kg, 15 kg, and 20 kg) and height of holding a load (50 cm, 70 cm, and 90 cm). Ten male subjects participated in a repeated measures experiment in which 9 lifts were performed. The time of holding a load was for 10 sec. The sampling interval was 1 msec. The basic measures of postural stability (mean distance of the COP, mean velocity of the COP, and sway area) and the chaotic measures (fractal dimension and first Lyapunov exponent) of the COP were calculated. When the holding height increased, the mean velocity of the COP tended to increase but the first Lyapunov exponent of the COP decreased. On the other hand, the fractal dimension of the COP decreased with the increase in load weight. From the above results, it was clarified that physical workloads (load weight and holding height) affect the chaotic measures of the COP. It was implied that the physical workload can be measured by the chaotic features of the COP.

KW - Body sway

KW - Chaotic analysis

KW - First Lyapunov exponent

KW - Fractal dimension

KW - Holding task

UR - http://www.scopus.com/inward/record.url?scp=72149115185&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=72149115185&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:72149115185

VL - 75

SP - 2553

EP - 2559

JO - Nippon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C

JF - Nippon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C

SN - 0387-5024

IS - 757

ER -