This cross-sectional study proposes two relative strength indexes in order to evaluate the risks of lower mobility in healthy older adults: 1) handgrip strength on body mass index and 2) quadriceps strength on body weight. Nine hundred and four men and women aged between 67-84 years old were tested for body composition, muscle strength and mobility function. Individuals in the lowest and middle tertiles of relative handgrip strength were respectively 2.2 (1.3-3.7) and 4.4 (2.6-7.6) more likely to have a lower mobility score. As for relative quadriceps strength, odd ratios for lowest and middle tertiles were respectively 2.8 (1.6-4.9) and 6.9 (3.9-12.1). Relative strength indexes, either using handgrip strength or quadriceps strength, are convenient to use in large scale studies and clinical practice.