# Limitations of Methods for Determining the Position of The Center of Mass of a Human Subject Performing a Sit-up

David A. Turcic

Spring 1997

6-13-1997

Thesis

## Degree Name

Master of Science (M.S.) in Mechanical Engineering

## Department

Mechanical Engineering

English

## Subjects

Abdominal exercises-- Physiological aspects, Human mechanics, Human locomotion, Anthropometry

## DOI

10.15760/etd.8145

## Physical Description

1 online resource (133 pages)

## Abstract

The knowledge of the position of the center of mass of a human subject performing a sit-up could help us understand the coordination of the sit-up motion. This thesis investigates the limits in three methods of determining the center of mass of a human subject. The three methods are the anthropometric method, the dynamic method, and the static torque method. The anthropometric method is a standard method that uses measurements of the subject to estimate the mass properties of individual segments of the body. The center of mass of the body is calculated from the mass and positions of the center of mass of the segments. A Monte Carlo simulation was executed to calculate the uncertainty of using the anthropometric method. Estimated errors were introduced in the Monte Carlo simulation to determine the uncertainty of the center of mass calculation. The results of the analysis show that the uncertainty of the center of mass calculation is ± 2.66 cm for this model. The largest contribution of the uncertainty is the estimation of the mass of the segment. The dynamic method used the relations between the mass properties, the motion and ground reaction forces to solve the least squares approximation for the mass and moments of inertia of the segments. The least squares approximation resulted negative masses and moments of inertia for some of the segments. The static method does not require separate knowledge of the mass and location of the center of mass. This method determines two coefficients per segment that combine the mass and its location. The center of mass of the body can be calculated from the location and angle of orientation of the segments. This method was determined to be limited by the precision of the force platform measurements.

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