Handgrip Dynamometry (HGD)

Ageing results in a loss of FFM and it has been shown that as FFM is lost, so strength and function will also decline (Janssen et al., 2002b; Goodpaster et al., 2006; Delmonico et al., 2009). HGD is positively correlated with both BMI and FFM but improvements in strength as measured by HGD have been shown to occur without increases in FFM or changes in BMI (Vernon & Hill 1998). HGD can therefore indicate changes in strength and function across a range of people of different nutritional status and body compositions (Martin et al., 1985; Heimburger et al., 2000). Muscle strength is a more important marker of muscle quality and thus function than muscle mass. It is this functionality of the muscle rather than muscle size which determines muscle function and influences survival (Wang et al., 2005, Gale et al., 2006).

A number of studies have shown that muscle strength plays an important role in terms of predicting functional limitation and ill-heath. In a prospective study of 3,075 men and women where muscle area and fat infiltration of muscle were measured by CT along with markers of strength it was found that only muscle attenuation (i.e. fat infiltration) and muscle strength could independently predict subsequent mobility loss with ageing (Visser et al., 2005). These results are supported by a separate study of 2,292 American men and women aged 70–79 years of age where a strong association between muscle strength (which included HGD measurements) and mortality was found with the crude hazard ratio (HR) for mortality based on grip

strength being 1.36 (95% CI 1.13,1.64) for men and 1.84 (95% CI 1.28,2.65) for women (Newman et al., 2006). More recently a study of 1,705 community dwelling older adults had muscle strength measured by HGD, skeletal mass measured by DEXA and levels of disability recorded and it was shown that muscle strength was the best measure of both age-related muscle change and functional impairment (Hairi et al., 2010).

The evidence to support measuring muscle strength is compelling although when considering muscle quality which influences strength some consideration has to be given to FM. A study of 2,307 older men and women found that in those people who had a greater FM there was a greater decline in FFM and it was this increased FM which was associated with lower muscle quality and also predicted faster rates of loss of FFM (Koster et al., 2011). It is therefore likely that preventing the accumulation of FM has the potential to maintain muscle quality which may in turn reduce disability and mobility deficits. Measuring FFM and FM alone will not then provide information about strength and function and so alternative more reliable measures need to be utilised. HGD has the potential to do this as HGD is a cheap, reliable, easy to perform measure and has been shown to be an accurate measure of muscle strength (Roberts et al., 2011).

Whilst HGD is a single task, and there is an obvious association with upper body strength, it has been shown to be correlated with overall body strength (Tietjen-Smith et al., 2006). HGD can be used to characterise overall muscle strength as it correlates with elbow flexion strength (men r=.638, p<.001, women r=.672 p<.001), knee extension strength (men r=.524, p<.001, women r=.514 p<.001), and trunk extension strength (men r=.515, p<.001, women r=.541 p<.001) giving an approximation of total body muscle strength (Rantanen et al., 1994). This is true for

the entire adult population including the oldest old (Tietjen-Smith et al., 2006). As a result it has been used in epidemiological studies of healthy individuals to measure strength and function (Bohannon, 1998; Rantanen et al., 2003). Although hand grip is primarily used as a measure of strength and endurance (Rantanen et al., 2003) there is a positive correlation seen with FFM and functional ability measured by HGD (r=.39, p=.0005) (Payette et al., 1998). It therefore also provides an indication of a person’s ability to perform activities such as opening containers, lifting weights and the ability to hold onto to handrails and to climb stairs (Skelton et al., 1994). It is this muscle strength ability which may be more important than aerobic fitness for independent living. Indeed in a study of 555 adults, aged 85 years, who were followed up prospectively, those who had a lower handgrip strength at baseline, had poorer functional ability and an accelerated decline in both ADL and cognitive ability (Taekema et al., 2010). There appears to be a linear relationship between handgrip strength and incident disability for ADL and as such HGD plays a role in predicting accelerated dependency in ADL.

There is an obvious role for measuring HGD to predict functional ability and an ability to perform ADL but perhaps more importantly it can also be shown to be an accurate predictor of mortality in the older adult (Rantanen et al., 2003). This has been confirmed more recently by Newman et al. (2006) and Cawthon et al. (2009).

The study by Cawthon et al. (2009) showed that HGD acts as a surrogate measure of overall physical functioning which in turn consistently predicts health-related outcomes such as premature mortality, disability, and other health-related complications among middle-aged and older adults. This study which included more than 3,000 older adults found that participants with the weakest grip strength were at greater risk of hospitalisation. Further data from a systematic review of the use of HGD as a predictor of outcomes in older people showed that low grip strength was a

consistent predictor of death and with the exception of two studies which recruited participants with rheumatoid arthritis, a high grip strength was a consistent predictor of survival across all ages (Bohannon, 2008). The results from this systematic review were conclusive although it should be noted that there were some inconsistencies in results between genders within the studies included in the systematic review. This may have been due to lack of detail within some studies around methodology and this could explain some of these inconsistences. In the same systematic review all studies examining the relationship of grip strength with future disability demonstrated that low grip strength was associated with a greater risk of functional disability. Indeed a key finding of this systematic review was that in many of the studies which included grip strength it was a consistent predictor of outcomes.

Since the publication of that systematic review further research has provided evidence to support these findings. In a group of 555 Dutch older adults (361f, 194m) aged 85 years and over those with the lowest handgrip strength at baseline had the highest rates of all-cause mortality at follow-up (Ling et al., 2010). In those people who had the greatest loss of handgrip strength over the follow up period there was also an increased risk of all-cause mortality irrespective of baseline measurements. Whilst handgrip strength can be utilised to predict outcomes it also has a predictive value in terms of recovery in older people. In a sample of 504 patients (120m, 384f, mean±sd age 85.3±5.5 years) who had undergone hip fracture surgery, grip strength was directly associated with the probability of both incident and persistent walking recovery (Savino et al., 2013). There is therefore great interest in the use of HGD as a marker of muscle strength and the role this plays in predicting functional limitations.

Handgrip measurements can be used as an important marker not only of strength and function but also to predict outcome. These studies therefore confirm that measuring HGD in an older population can act as an inexpensive, reliable screening measurement for assessing deterioration in muscle strength, functional ability and ability to perform ADL and thus potentially to live independently. There are a number of other factors in addition to changes in muscle mass and quality which negatively influence handgrip strength in a healthy older population including inflammation (Qureshi et al., 2002; Rantanen et al., 2003; Wang et al., 2005; Hamer

& Molloy 2009; Schaap et al., 2009), and low levels of physical activity (Kuh et al., 2005). These associations may help to explain the relationship between handgrip and outcomes and indeed further support the use of HGD as a screening measure in an older adult population.

Due to its ease of use and portability HGD is commonly used as a simple bedside tool because it is a valid surrogate measure of overall muscular strength. Its role in this has been acknowledged within the diagnosis of sarcopenia as it is one of the accepted diagnostic markers (Cruz-Jentoft et al., 2010). The interpretation of HGD measurements requires reference or normative values for comparison and there have been several suggested cut-offs for normal handgrip levels published. In a study of 4,000 older adult Chinese people, HGD was found to be a suitable indicator of frailty within the community setting and in this study, cut-off values of 28 kg for older men and 18 kg for older women were recommended (Auyeung et al., 2014).

The purpose of this study was to screen for frailty and as such these cut-offs have been suggested with this in mind. This is the most recently available data and it encompasses a large number of participants but whether these values are appropriate for the UK population is not clear. There are known differences in body composition across different ethnic groups (Wagner & Heyward, 2000; Wang et al.,

2003) and it is feasible that there are differences in functional abilities as a result. It may therefore be more appropriate to use the cut-offs suggested by Cruz-Jentoft et al. (2010) when considering sarcopenia and sarcopenic obesity. These cut-offs are

<30 kg men and <20 kg for women. These are appropriate for their diagnostic value for sarcopenia but this does not apply to the entire older adult population and for comparison to normal values across the population. Normative values from Bohannon et al. (2006) may therefore be more appropriate. This meta-analysis of grip strength measurements has consolidated the data available and those relevant to older adults are shown in table 1.3.

Table 1.3 Consolidated grip strength values for males and females (adapted from Bohannon et al., 2006) reasonable threshold for determining impaired muscle function (Bohannon et al., 2006). HGD provides important information about strength and function but does not provide an overall picture in terms of functional ability and performance in ADL and complementary measures will provide additional value when measuring function in older adults.