Evaluation of Anthropometric Requirements for the Design of an Ergometer Restraint System 2001-01-2186

NTE is developing a system for neuromuscular research (MARES: Muscular Atrophy Research and Exercise System). This system is an ergometer to be flown and installed in the International Space Station in the year 2004 and is consisting of a motor, an HRS (Human Restraint System) and a control electronics that controls the motor. The subject is connected to the motor by means of the restraining system HRS. This ergometer can be used for 11 movements (wrist flexion/extension, pronation/supination and radial/ulnar deviation, trunk flexion/extension, arm pull/press, leg pull/press, elbow flexion/extension, Shoulder flexion/extension, hip flexion/extension, knee flexion/extension and ankle dorsal/plantar flexion).

MARES is a research tool for physiologists, but also interesting for human factors people. It is a tool to quantitatively measure the physical condition of a person before performing a physically demanding task (e.g. EVA), a tool for health monitoring and to verify the efficiency of countermeasures against microgravity deconditioning.

The HRS must meet the following anthropometric range: from 5 percentile Japanese female to a modified 95 percentile American male. A design report of the HRS was produced. This document included all the needed adjustments of the HRS to be compliant with all the population and with other requirements applied to the ergometer. One of the characteristics of this HRS is that the number of adjustments is high. Comments on why such a big number of adjustments were needed arose among reviewers of the system. We would like to clarify what are the different influences of the requirements on that high number of adjustments. An analysis on the influence of the anthropometrics on the number of adjustments of the system is supplied in this paper.

Tests to assess the validity of that HRS were carried out with a broad population. We present in this paper one of these tests: comparison test of three ankle dorsal/plantar flexion adapters. These adapters were the following: a commercial adapter from a commercial ergometer, an adapter already flown in the Space Shuttle and the ankle adapter manufactured according to the HRS design report.

These tests evaluated the performance of the adapters in a population of six people covering from 5 percentile Japanese female to a modified 95 percentile American male and considering the following variables: joint alignment with motor axis and comfort level.

All adapters show no significant difference between comfort level (p<0.05). The joint alignment with motor axis was better in HRS adapter and significantly worse in the commercial and the flown adapter (p<0.05).

As the adapter of HRS has to be compliant with such joint alignment requirements, the number of adjustments of a single adapter is much higher than in the other cases. This implies a heavier adapter than in the other cases that have less adjustments in the following order: flown adapter and commercial adapter.

From the results obtained, we can conclude that requirements referring to a broad population imply heavier and harder-to-use hardware. It can also be indicated that the joint alignment requirements imply a high number of adjustments. These two requirements imply a harder to operate and heavier hardware, but a satisfactory scientific equipment that can be used by a broad population. Depending on the type of experiment to be performed, a compromise should be pursued.