The Development of a Home-use Method for Evaluating Muscular Strength of Lower Limbs

Abstract

The decrease in muscular strength of the lower limbs due to aging is a serious problem for elderly people, since it relates to locomotive disability and falls and consequently decreases the quality of life. However, according to the suggestions in previous studies, we can prevent the muscular strength from decreasing by performing appropriate strength training in daily life. To advance the training appropriately, it is necessary to evaluate current muscular strength objectively and to ascertain effectiveness of the training. However, the access to resources for measuring muscular strength is currently limited for many people. Therefore, we have developed a home-use method to evaluate muscular strength. With regard to usability under general home conditions, it is important that users can intuitively understand the result of the muscular strength test. Therefore, we define a new index of muscular strength of the lower limbs, which we named “muscular strength margin”. This index shows the muscular strength normalized by the minimally required muscular strength for daily activities. This index is easier to understand than the muscular strength itself. For example, if the index does not reach 100%, the result means that the muscular strength is lower than the level required for daily life. When the index is 200%, the result means that the muscle is twice as strong as the required level. Additionally, for easy measurement and cost reduction, we utilize a micro-electro-mechanical system acceleration sensor and a gyro sensor, instead of the force sensor, to measure muscle strength. To evaluate the practical validity of “muscular strength margin” as a new index of muscular strength, the muscular strength margin was measured in 98 subjects. The results were consistent with those of previous studies. Additionally, the findings suggest that the value of 100% is a valid guide to evaluate the presence or absence of sufficient muscular strength of the lower limbs. The current method introduced in this article has potential as a beneficial home-use method of evaluating muscular strength.