Date of Award

Spring 2018

Document Type


Degree Name

Doctor of Philosophy (PhD)


Human Movement Sciences

Committee Director

Daniel M. Russell

Committee Member

Steven Morrison

Committee Member

David Swain


When holding an outstretched limb or aiming at a target, humans produce small involuntary fluctuations that may hamper performance. Current strategies for minimizing the impact of tremulous oscillations predominantly include both extrinsic and intrinsic support. The aim of the current dissertation is to better understand the parameters of physiological tremor associated with handgun aiming with the end goal of improving shooting accuracy. Experiment 1 focused on handgun aiming and the influence of different arm posture adopted during aiming. Experiment 2 expanded upon the findings of experiment 1 by comparing tremor during finger pointing, handgun aiming, and handgun shooting. Experiment 3 attempted to confirm that both mechanical support and proprioceptive feedback play a role in both attenuation of tremor amplitude and handgun shooting accuracy.

In experiment 1, thirty volunteers stood 6.4 meters from a target and aimed a weighted mock handgun for 10 seconds per trial. Two hand grips (bilateral, unilateral) and two arm positions (bent elbow, straight elbow) were assessed for acceleration in the anterior-posterior (AP), medial-lateral (ML), and vertical (VT) directions. Amplitude, regularity, and a frequency spectrum analysis of the acceleration signals were analyzed. Tremor amplitudes (VT, ML) were reduced using a bilateral grip and by bending the elbows. The irregularity of the tremor signal was increased by using two hands to support the handgun. Interestingly, irrespective of the posture adopted, ML accelerations were of greater amplitude than VT oscillations. AP oscillations were markedly smaller compared to VT and ML tremor, did not display consistent frequency peaks, and were not altered by the arm conditions.

During experiment 2, twenty volunteers, in a counterbalanced order, pointed their finger, aimed a training handgun, or shot a training handgun, for 10 seconds at a bullseye target 6.4 meters away. Amplitude, regularity, and frequency spectrum analysis of the acceleration signals were computed. Aiming with the mass of a gun in the hand has primarily a damping effect on the amplitude of tremor in the distal segments as well as resulting in more regular movements. Overall, aiming with a gun and pointing with a finger were similar tasks except for the added mass of the handgun aiming condition. Shooting accuracy and handgun shooting experience were also assessed for correlations with acceleration amplitude and regularity. Both handgun shooting accuracy and experience revealed a stronger correlation with increased irregularity of the acceleration signal than decreased acceleration amplitude. A correlation was also run between shooting accuracy and handgun shooting experience. An increase in accuracy had a significant, moderate relationship with an increase in handgun shooting experience.

Experiment 3 had twenty volunteers aim as well as shoot a training handgun at a bullseye target 6.4 meters away during two limb support conditions and two weight conditions for a total of four combinations. Amplitude, regularity, and frequency spectrum analysis of the acceleration signals were computed. Bilateral limb support again reduced tremor amplitude and increased the irregularity of the acceleration signal over unilateral conditions. Bilateral limb support also contributed to a significantly improved handgun shooting accuracy when compared to unilateral limb support conditions. By manipulating the weight of the handgun, the third study also indicated the addition of a second limb reduced acceleration amplitude through both mechanical support and proprioceptive feedback.

The experiments demonstrate that finger pointing and handgun aiming share similar tremulous characteristics in all three directions (VT, ML, AP). These experiments also indicate that acceleration amplitude can be reduced while acceleration regularity and shooting accuracy are increased through the use of a bilateral limb support posture.


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