A psychophysical investigation of hand muscle fatigue due to a combination of isometric and isotonic forces.

摘要

In any given industry, most operations are performed by hand. Hand grip strength is an important factor that can influence performance in terms of the amount of force a person can apply and his/her endurance limit (or time to fatigue). This research attempts to discover the relationships among maximum hand grip strength (maximum voluntary contraction or MVC), holding time, use of gloves, three different wrist postures (neutral, pronation, and supination), Gender, Body Mass Index (BMI), Hand Grip Circumference, Resting Heart Rate, and the number of Cycles/Time before a hand muscle fatigues. A psychophysical approach, which is based on an individual's perception of pain index, is used to measure the endurance (Cycles/Time to fatigue). The findings from the research could help design work tasks effectively as well as design the tools with which they are performed ergonomically.;The research explored the available literature on the topic of hand muscle fatigue and has found that no formal study has been conducted in the area of the combined effects of static and dynamic forces with regard to hand muscle fatigue. A pilot study was conducted to explore the feasibility of full scale research. Sixteen subjects participated in the pilot experiment. The instrumentation included a Hand Grip Dynamometer, Gollehon Extendable Goniometer, Pulse-Oximeter, and a stop watch. The data from the experiment was analyzed using MANOVA/ANOVA and the results indicated that there was potential for additional research. The pilot study helped refine the overall framework for the actual research.;A total of 78 subjects participated in the actual experiment. A summary of the important findings is as follows: Males can exert a 60% higher MVC as well as 23% more Cycles to Fatigue compared to females. The use of gloves decreased the endurance (Cycles/Time to Fatigue) for females by about 10%. Subjects with a high BMI (BMI >24.9) endure 18% more Time to Fatigue. In addition, subjects with a large Hand Grip Circumference (greater than 17 Centimeters) can exert a 47% higher MVC compared to subjects with a small hand grip circumference (less than or equal to 15 Centimeters). Subjects with a resting heart rate of 65 or below have a 20% higher MVC compared to subjects with resting heart rate above 75. A neutral hand posture with a holding time of five seconds improves the endurance (Cycles/Time to Fatigue) by 7%, when compared with the pronine and supine wrist postures.;The findings of this research can be applied to domains, such as the recruitment of military/police/athletic/firefighting personnel, and design of tools and tasks. A sample chart benchmarking MVC and endurance (Number of Cycles to Fatigue) is developed as one of the guidelines for the recruitment of military/Police/Firefighting personnel as well as rehabilitating patients with hand injuries. Considering that the use of gloves decreased the endurance, alternatives such as rubber lining the tools should be considered for use in the future. The findings from the current research are applicable to college students within the age group of 18 to 21.;The experiment conducted in this research can be extended to other age groups as well as other domains for wider applications.