rapid population aging poses serious social challenges worldwide . for example , unprecedented aging is progressing rapidly in asian nations including korea and japan . although the definition of an aged individual varies depending on the cultural and social environments of each country , an elderly person is defined as a person 65 years or older , which aligns with the definition adopted by gerontologists1 ) . by this standard , japan became a super - aged society in 2007 , as 22% of its population was > 65 years old . furthermore , korea has been projected to become a super - aged society by 20262 ) . as we are witnessing today , population aging is an inevitable phenomenon occurring throughout the world including western countries and japan , and is attributable to a complex mixture of economic , medical , educational and others factors . consequently , aging poses social problems such as labor shortages and public health issues , such as osteoporotic fractures . the dramatic increase in the average life span in korea has raised the public 's interest regarding ways of not only living longer , but also reaching old age in good health . therefore , healthy aging has also become a major public concern and active area of study in geriatric medicine , with an emphasis on the exploration of an array of strategies designed to improve quality of life of life in the elderly population3 ) . instead of a traditional approach , which accepts a variety of pathological symptoms as natural consequences occurring in elderly populations , we introduce evedience to support a different theory ; pathological symptoms as a series of consequences attrubutable to the frailty syndrome . this syndrome occurs when the functioning of several organs diminishes and biological reserve declines below healthy levels . unlike normal aging , however , frailty is characterized by increased vulnerability to several disorders after exposure to the same stressful situation45 ) . even though frailty is a common syndrome in older adults , it is not an inevitable part of the aging process , as only a segment of the elderly population experience this syndrome . although several frailty - defining criteria have been proposed , frailty has been defined as meeting three of the five criteria presented in table 1 . additionally , a pre - frail stage has been defined as meeting one or two of the criteria5 ) . not only is frailty considered a clinical syndrome that can be discriminated distinctively from normal aging and progressive physiological changes , but it is also one of the stages in the progression from normal aging to the pre - frail stage , subsequent frailty syndrome , and ultimately , geriatric disease itself4 ) . the clinical manifestations of frailty are weight loss , sarcopenia , low physical activity , a diminished sense of balance and gait speed , diminished cognitive functioning , and nutritional deficiency . therefore , frailty carries an increased risk for poor functioning in activities of daily living including locomotive abilities , the incidence of cardiovascular diseases , cancers , falls , and mortality6 ) . the results from a large number of studies verified that frailty was profoundly related to osteopenia or osteoporosis , sarcopenia , and falls6 ) . as the clinical definition of frailty includes the diagnostic criteria for sarcopenia , one must be familiar with the definition of sarcopenia itself , which is the consistent and systematic loss of skeletal muscle mass and strength prevalent in older adults7 ) . rosenberg8 ) first proposed the term ' sarcopenia ' ( from the greek ' sarx ' for flesh and ' penia ' for loss ) to describe the observed age - associated decrease in muscle mass . when dual - energy x - ray absorptiometry ( dexa ) , computed tomography ( ct ) , magnetic resonance imaging ( mri ) , and other new radiological instruments began to appear , it became possible to measure relative masses according to human body compositions , such as fat , water , minerals , and skeletal muscle . there is little doubt that skeletal muscle mass decreases with aging , and it has been hypothesized that falls and fractures in the elderly are attributable to this loss of skeletal muscle mass . to date , a number of studies have been conducted in order to examine different aspects of the decline in skeletal muscle mass and strength using various methods , all of which verified that sarcopenia resulted in diminished vitality and quality of life and increased the risk of mortality6 ) . in 2010 , european researchers developed diagnostic guidelines for sarcopenia7 ) , which is initially determined by a decreased amount of muscle mass , followed by reduced levels of muscle strength and physical activity ( fig . , relative skeletal muscle mass also has to be measured using dexa , ct , and mri , among others . in relevant studies , the relative muscle mass was calculated as the total body skeletal mass divided by squared height9 ) or weight10 ) . although the diagnostic criteria varied slightly across the different studies , class ii sarcopenia was typically defined as a skeletal mass index < 2 standard deviations below mean values for young adults , and was considered to be clinically significant . the standard values of korean men and women in domestic studies were used as a reference base for the reviewed studies11 ) . according to the results of a cross - sectional study , older adults had a 25 - 35% smaller lower extremity muscle mass than younger adults , and age - related loss of muscle mass occured at a rate of 1% annually , dropping continuously up to 40% smaller between those in their 20s and those in their 60s3 ) . lower extremity muscle strength decreased at a rate of 3% annually , and the muscle power of older adults was 20 - 40% lower than that of younger adults12 ) . when comparing muscle strength differences between men and women , the rate of muscle loss was found to be somewhat similar , but the absolute reduction of muscle mass was observed to be greater in men3 ) . in order to accurately measure muscle power , because this method is not applicable to all patients , grip strength has been a commonly applied measured due to the suggestion that it can be used to relatively and precisely represent lower extremity muscle power13 ) . gait speed has been measured to assess physical activity levels , and a low gait speed ( defined as a walking speed < 0.8 m / s ) is part of the diagnostic criteria for sarcopenia according to the european working group on sarcopenia in older people7 ) . more recently , some asian investigators have proposed that a walking speed < 1 - 1.2 m / s would be more appropriate than the european standards1 ) . furthermore , other useful methods have been suggested including the short physical performance battery and the timed - up - and - go test . according to asian clinicians , however , measuring gait speed using a walking distance of 6 m is considered as a repeatable and practical measure . according to the findings derived from a meta - analysis , sarcopenia was found to be the root cause of falls in a a vriety of studies , increasing the risk of falls by up to 1.5 - 3.0 fold14 ) . moreover , the results of a previous study demonstrated that the weakened strength of the upper limb muscles increased the risk of falls by up to 1.4 - 1.5 fold14 ) . therefore , the loss of muscle strength is an important indicator for predicting the incidence of falls . additionally , the results of biomechanical studies and electromyography have revealed that older individuals with sarcopenia had slower contraction and response rates in their lower limb muscles15 ) , and that muscle strength had declined16 ) . although body balance is more easily restored in younger people , it my not be maintained properly in older individuals and can influence thier propensity to fall . sarcopenia is associated with diminished physical activity levels , incident disability , and is a major component of frailty . collectivelly , these findings may explain the pathologic mechanisms underlying sarcopenia as a leading cause of higher rates of frailty . the results of previous studies have indicated that the cross section muscle of the thigh , the degree of fat infiltration , and muscle strength , among others , were vital factors for predicting incident disability , and that fat infiltration and muscle power were more crucial criteria than muscle mass17 ) . regardless of bone mineral density ( bmd ) , the degree of fatty infiltration in muscles has been found to increase the risk of hip fractures18 ) . additional studies exploring the role of sarcopenia in relation to the aforementioned finding therefore seem to be warranted . as recent findings have revealed that muscle fat infiltration can be caused by obesity , sarcopenic obesity has been drawing increased attention19 ) . the function and formation of bones and muscles are closely related20 ) , and skeletal shape is determined by loads changing as muscle strength and size increase21 ) . as a result of muscle loss occurring after the age of 50 years , the workload imposed on the skeleton gradually decreases , and atrophy of bone - muscle unit can be observed . the age - related loss of bone and muscle mass occurs almost simultaneously , and the loss of muscle mass is predominantly detected in type ii fibers . consequently , the entire bone - muscle unit is reduced to 50% in elderly adults as compared with young adults . these two biological outcomes involve similar hormonal changes , and abnormal hormonal effects on the growth hormone / insulin - like growth factor-1/phosphoinositide 3-kinase / akt pathway has been suggested to have the potential to induce the osteoporosis associated with sarcopenia22 ) . it has been speculated that vitamin d may be one of the mediators of muscle and bone weakening , and this assertion was validated by the results of a study that found patients with decreased vitamin d levels experienced muscle and bone weakening23 ) . due to the results generated from a number of recent studies which indicated that vitamin d was primarily involved in physiological changes in the bones and muscles , as well as those showing that vitamin d insufficiency was a main contributor to sarcopenia and osteoporosis , the results from a previous study suggested that sarcopenia and osteoporosis acted as a kind of ' hazardous duet ' , eventually leading to frailty2425 ) . however , it remained uncertain as to whether the interaction of osteoporosis and inadequate skeletal muscle mass affected frailty , or whether the separate conditions made individual contributions . the aforementioned study reported that frailty was six times more likely to occur in patients with both conditions , strongly suggesting that the interaction of the two conditions contributes to frailty . alternatively , treating osteoporosis or increasing muscle mass can be solutions to the problem . the results of one study indicated that an increase in bmd and sarcopenia treatment could be achieved concurrently through osteoporosis management26 ) . moreover , the results of a study involving a muscle building workout regimen indicated a simultaneous increase in bmd , supporting this alternate hypothesis27 ) . however , contradictory results regarding whether the combination of osteoporosis and sarcopenia played a significant role in the problem in clinical trials19 ) suggest that further studies are warranted . the development of a broad array of medications , as well as the clinical trials associated with these medications , are currently in progress . these efforts are expected to provide new options for the treatment of osteoporosis and sarcopenia . the immediate goals of such research are to develop the effective strategies required to overcome geriatric frailty , which can only be found through medical research , treatment , and a multidisciplinary approach .
public health strategies designed to accomodate the ever - increasing human lifespan are urgently required . a good clinical understanding of frailty , as well as knowledge regarding how to prevent it , 
 will therefore be required in order to overcome this challenge . 
 sarcopenia is an important component of the frailty syndrome , and its association with osteoporosis can lead to fractures and incident disability . therefore , 
 this review examined the literatuire pertaining to the association of sarcopenia with osteoporosis in order to assess preventive strategies .