The findings of this study indicate that a significant proportion of elderly subjects aged 60 years and more may experience an incident fall over the previous year. Weakness of quadriceps muscles and age > 70 years were independently associated with falls.
Occurrence of falls in the elderly subjects are common and its prevention is important because, falls account for 87% of all osteoporotic fractures in the elderly  and fall-related injuries is associated with significant economic costs suggesting effective preventive strategies to decrease the incidence and healthcare expense of these injuries .
The results of a systematic review of the relevant studies showed that, impaired balance and gait, polypharmacy, history of previous falls, advancing age, female gender, visual impairments, cognitive decline especially attention and executive dysfunction, and environmental factors were the major risk factors of falls in older adults .
A systematic review and meta-analysis of 30 studies demonstrated that muscle weakness especially lower limbs muscle weakness were the most important factor of occurrence and recurrences of falls . Another systematic review of 21 studies, which have addressed the incidence and risk factors of falls in the Chines older people showed, fall rates between 14.7 and 34%. The associated factors were female sex, older age, use of multiple medications, gait instability, fear of falling, and decline in activities of daily living .
However, depending on the study design, duration of follow-up and characteristics of the study population, the prevalence and the causes of falls vary across diverse studies and changes from 13 to 64.5% across different studies [3, 23,24,25,26,27,28].
The results of this study indicate a significantly negative association of QMS with the development of incident falls. The prevalence of falls in these patients increased from 9.3% in individuals with QMS > 30 kg to 23.5% in those with QMS lower than 15 kg. These findings are in agreement with the results of other studies [1, 9, 12, 21, 23, 29, 30]. In a study by Ikoez et al., 18% of falls have been attributed to quadriceps muscle weakness . In another prospective 3-year longitudinal study, quadriceps muscle strength was predictor incident falls amongst community-dwelling older women at high risk of fracture .
These observations indicate a potential role for QMS in predicting future development of falls in older people. Higher risk of falls in older age groups of this study should be also attributed to muscle weakness due to aging. By aging the ability of muscle to regeneration, repair and remodeling diminishes, which results in age-related loss of skeletal mass and strength. In addition, muscle degeneration in older subjects reduces muscle power and mass. These changes may affect maintaining body balance [29, 31]. Although the association of female sex with falls in this study diminished to no significant level but other studies have reported higher prevalence of falls in women [23,24,25,26]. Women may be more susceptible to falls, because, several associated factors of falls such as osteoporosis, osteoarthritis, obesity and vitamin D deficiency are more prevalent in women [15, 32,33,34,35]. Lack of association in this study may be explained by high frequency of these factors in the control group. Therefore, a significant association might be detected in a study with larger sample size.
In this study, the association of several factors such as obesity, osteoporosis, vitamin D deficiency, hypertension and visual impairment with fall did not reach to a statistical level (Table 1). Vitamin D deficiency affect antigravity effects of lower limb muscles which are responsible for postural balance and correction of deficiency may decrease the occurrence of falls in the elderly . Vitamin D deficiency is associated with QMS as well as knee osteoarthritis. Normalization of vitamin D improves quadriceps muscle strength [15, 18, 20, 37,38,39].The relationship between knee or hip osteoarthritis as well as obesity with increased risk of falls has been shown [40, 41]. However, lack of association in this study should be explained by high prevalence of these factors in the general population. A study with larger sample would be required to confirm these findings.
This study has limitations regarding the study design which is cross-sectional and the observed association does not indicate causality. Another limitation of this study may be attributed to the method of data collection in respect to incident falls, which was based on self-reported data. It is possible that a proportion of elderly patients could not remember past occurrence of falls, because of cognitive or attention impairment, and the prevalence of falls being underestimated.
The strength of study is based on patient selection which comprised all eligible participants of the Amikola Cohort Study. Collection of data by using validated questionnaire. Furthermore, complete clinical and laboratory examinations of all participants should be also considered strength.