This study aims to answer the following problem: Which of the two physical exercise modalities (strength training or aqua aerobics) produces better results, after a six-month longitudinal intervention, in functional fitness, cardiorespiratory fitness, bone mineral density, subjective well-being, body satisfaction and general health perception in elderly women? Due to the large number of dependent variables, our thesis is structured into three studies that will answer the following questions: What is the effect of 6 months of strength training vs. water aerobics on the functional and cardiorespiratory fitness of elderly women; What is the effect of 6 months of strength training vs. water aerobics on the bone mineral density of elderly women and What is the effect of 6 months of strength training vs. water aerobics on the subjective well-being, body satisfaction and general health perception of elderly women?".