Investigation of the Effect of Exertion Length on Measured Isometric Strength

Isometric strength testing has been shown to be an effective method of matching employee strength capability to job strength requirements. Increased blood pressure and other cardiovascular effects produce undesirable stress in test subjects and could be reduced by using a shorter test if no additional information is gained by using a longer test. If several muscle groups are involved in an isometric strength test the “Ergonomics Guides for Assessment of Human Static Strength” suggests that pilot studies be performed to assure adequate time for a subject to seek and maintain a maximum voluntary effort for a period of at least three seconds. This study was designed to quantitatively investigate the effect of exertion length on measured strength for three strength tests simulating industrial activities. Twenty student volunteer subjects (10 M, 10 F) performed each test for both a five second and three second duration. The force measured during selected one to four second intervals or both the five second and three second tests were compared. This study indicates that it may be possible to decrease the length of isometric tests without reducing the validity of resulting strength measurements, thus reducing the stress on the subjects.