This study examined the ergonomic effects of a specially made knee supporter containing spiral bone springs aimed at reducing physical stress on the leg muscles during sit-to-stand (STS) and walking. Twelve young females and fifteen elderly subjects performed STS and treadmill walking with and without a specially made supporter, which may be a simple device for aiding STS and/or walking. During STS, electromyography (EMG) was observed from the vastus lateralis of the right leg. The root mean square (RMS) and mean power frequency (MPF) were calculated from the observed EMG. The changing rate of maximal leg acceleration, the third time derivative of the leg position, was also assessed during treadmill walking at a freely chosen stride frequency and speed. A significant decrease in the RMS was observed during STS when wearing the supporter in both groups. A significant increase in the changing rate of maximal leg acceleration was found during walking with the supporter in both groups. MPF significantly increased when wearing the supporter only in the young group. These results showed that the supporter with spiral bone springs reduced physical stress placed on the quadriceps muscles during STS and walking. This ergonomic contrivance will reduce the possible “risk” of stumbling and/or falling in elderly individuals. The reduced physical burden on the quadriceps muscles will also reduce or delay muscle fatigue, which will further result in an increase in the amount of daily physical activities exhibited in physically poor populations.