Comparison between load-cell dynamometer and spring dynamometer in the measurement of back strength

Abstract

The purpose of this study was to compare the load-cell dynamometer with the spring dynamometer in the measurement of back strength. Two experiments were designed to investigate the differences and the relationship between the testing methods by use of the said two dynamometers. In experiment 1, six male university students were used. Each subject was tested three times a day with each dynamometer and the same tests were administered on other two days. To analyze the changes in the angles of the shoulder, hip and knee joints, all tests were filmed with 16mm high speed motion camera. In experiment 2, 13 male subjects were used to examine the relationship between the length of the chain of the load-cell dynamometer and the back strength recordings. The angle of the hip joint was controlled by changing the length of the chain in this experiment. The differences between the recordings by use of load-cell dynamometer and by use of the spring dynamometer among six subjects in experiment l and 13subjects in experiment 2 were examined. The reasons for the difference were further investigated by analyzing the body motion applying 16 mm film analyser when changing the degree of the hip joint in testing. The results were summarised as follows: 1) The mean strength measured by the load-cell dynamometer was lower than that by the spring dynamometer for all subjects in experiment 1 and eleven subjects in experiment 2. 2) The changes in the angles of the shoulder and the hip joint from the set position to the position of maximal strength were larger for the spring dynamometer. 3) The majority of subjects obtained greater strength when the chain was longer than the standard length. 4) The relationship between the back strength recordings by use of load-cell and by use of the spring dynamometer was not consistent, because individual differences were found to be rather large.