Parameter investigation for low frequency vibration of the forearm
Matz, Roger Edward
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The need to be able to predict the response of portions of the human body to dynamic loading has been well established, and it is the purpose of this study to experimentally investigate the effects of several independent parameters as they relate to the frequency response of a biological system. Specifically, the forearm of volunteer subjects was excited by a very small amplitude, sinusoidal forcing function at a position near the styloid process, and the response of the arm was measured with an accelerometer located near the olecranon process. The input forcing function frequency was automatically swept through a frequency range of 80 to 600 Hz, and the resultant output frequency response was recorded as a power spectral density curve by means of a wave analyzer. The natural frequencies of the arm were considered to be the frequencies at which relative peak amplitudes occur in the power spectral density curve. For each subject, four independent parameters, as well as the dependent variable (natural frequency), were measured. These four independent parameters were r (1) arm length as measured from elbow to wrist, (2) bone size as indicated by wrist size, (3) muscle development as indicated by the percent increase in upper arm circumference from unflexed to flexed position, and (4-) fleshiness as indicated by the ratio of unflexed upper arm circumference to wrist width. The subjects utilized were approximately 250 college-age males. The significance of the effects of each of the foregoing parameters, and of the interactions between these parameters, on the dependent variable was examined via a 2 n fixed factor, factorial experiment. The experimental results indicated all of the four factors significantly affected the resonant frequency at the 99% level of confidence. It was further determined that each of these factors had significant interactions, with all two way interactions except arm length-bone size and muscle development-fleshiness significant. All three way interactions were significant. No general trend was determined for any factor except bone size, for which an increase in level tended to cause a decrease in natural frequency. It was concluded that although other parameters may be found which affect the resonant frequency, these four were the ones of most importance.