## Changes in segment inertia proportions between 4 and 20 years

Reference | Changes in segment inertia proportions between 4 and 20 years |

Journal | J.Biomechanics, Vol.22,529-536 (1989) |

Author | R.K.Jensen |

Item | M COG I |

State | Living |

Sample number | 12 |

Sex | Male |

Age | 4-20 |

Measurement year | N/A |

Race | Caucasian |

Measurement place | N/A |

Measurement technique | Photogrammetry |

Raw data accessibility | NG |

Note）The data used in this study were collected annually over a 9-year period in a mixed longitudinal study.

#### (1)Definition of the body segmentation

Head,

Upper part of torso,

Lower part of torso,

Upper arm,

Forearm,

Hand,

Thigh,

Calf,

Foot,

Forearm+Hand,

Calf+Foot,

Torso,

Head+Upper arm+Torso,

Head+Torso

The definition of this study is based on the definition of Jensen (1986).

#### (2)Predictive model

The ratio of the segment mass, center of gravity, and radii of gyration are calculated using polynominal regression equations that includes age as an independent variable.

#### (3)Validation

Comparison between direct measurement of body weight and measurement by photogrammetry

→Error: less than 3%

# Regression coefficients

## The ratio of the segment mass

The following table shows regression coefficients.

The ratio of the segment mass is calculated as percentage of the body mass.

**Ex.)**

**The ratio of the head mass=0.2376-0.114×age**

## The ratio of the center of gravity

The following table shows regression coefficients.

The ratio of the COG is calculated as percentage of the segment length measured from the proximal end.

**Ex.)**

**The ratio of the COG of the lower part of torso(%)=0.47043+0.0092785×age-0.00034945×age ^{2}**

## The ratio of the radii of gyration

The following table shows regression coefficients.

The ratio of the radius of gyration is the ratio of the semiaxis of the body segment at the center of gravity to the segment length.

**Ex.)**

**The ratio of the radius of gyration of the Forearm+Hand(%)=0.25947+0.0036529×age-0.00016206×age ^{2}**