To our knowledge, this is the largest cohort study to report age and sex-specific values for objective measures of physical capability in British men and women. Using this data, we found that just over 1 in 4 community-based, older adults in our cohort would meet criteria for muscle mass measurement, if the EWGSOP algorithm for sarcopenia case-finding was applied. This could pose significant challenges to healthcare services, since measurement of muscle mass is not widely available in routine clinical practice.
Few studies have reported the numbers of older people falling below strength and performance thresholds suggested in the EWGSOP algorithm. Data from a recent report of another UK cohort revealed 22% of community-dwelling participants (aged 59-73 years old) enrolled in a physical performance sub-study met criteria for muscle mass measurement . This is comparable to our findings, with the slightly higher proportion reported here explained by the older ages of the participants included, with many older than 73 years. We found that age was strongly and inversely associated with physical capability, consistent with other reports [25–31]. Unadjusted results showed that usual walking speed declined by 0.01 m/s and grip strength by 0.54 kg (men) and 0.30 kg (women) per year. Thus, as age increases more people are likely to fall below the suggested physical capability thresholds necessitating muscle mass assessment and it is not surprising that our older cohort had higher numbers of participants in this category. The inverse association between physical capability and age and the ageing nature of many populations also suggests that the number of people likely to meet criteria necessitating muscle mass measurement is only likely to rise over the coming decades.
We found that a greater proportion of women than men fell below physical capability thresholds, of significance given the increasing numbers of older women in the population. This was despite the use of sex-specific grip strength criteria and reflects the greater functional dependency experienced by older women. Consistent with this, women had weaker grip strength than men, took longer to perform 5 chair stands and had poorer standing balance even after adjustment for age and anthropometry. This concurs with existing literature [25–31] and adds to the observed male-female health-survival paradox , since women are known to have longer life expectancies than men but lower physical capability is a factor associated with a higher risk of death. One possible explanation is that men decline faster than women and this is important for future health. Cross-sectional associations of absolute grip strength with age did show a steeper decline in men than women, but this difference substantially attenuated when the relative change with age was assessed. This suggests that the steeper decline of absolute strength in men is partly explained by the higher strength of young men compared to young women. However, a small age-sex interaction was still observed when relative change in strength was examined and mixed results have been reported from longitudinal studies examining this interaction [33–35]. Therefore, further work in this area is needed.
The age and sex associations reported here are remarkable in their similarity to those published from the HALCyon study group, after harmonisation and meta-analysis of independent participant data from eight, smaller and heterogenous UK cohorts (see Additional file 3) . Meta-analysis of individual participant data is increasingly advocated . However, large or well-known studies are more likely to be invited to share data creating possible bias and it is still uncertain how much studies can differ and yet still be combined in pooled analyses. Despite this, it is interesting that the size and direction of associations are very similar in this single, large British cohort to those reported in the meta-analysis.
The EWGSOP consensus definition  has provided a much needed opportunity to standardise sarcopenia research in order to progress efforts to untangle its underlying pathogenesis and develop potential therapies. Sarcopenia identified using this definition has been associated with poor self-reported health and physical function  and with future increased risk of mortality . However, the EWGSOP definition has been little scrutinised. A surprisingly low prevalence of sarcopenia (0.9%) was reported when using this definition in Finnish older women  and on examination of the algorithm’s component parts the authors found no association between functional performance and low muscle mass. The predictive power of low muscle mass has been debated previously. Associations with future disability and mortality  have been less consistent and strong [26, 40, 41] than associations between gait speed or muscle strength and future health-related outcomes [4, 5, 42, 43].
Maintenance of physical function with increasing age is important and although we found strong inverse associations between age and physical capability, we also report considerable variation in physical capability within older age-groups. Therefore, it is important to understand the factors leading to this heterogeneity and to develop interventions to mitigate the disability associated with older age and its considerable healthcare cost . However, currently suggested interventions for sarcopenia, such as resistance exercise training, are effective in a wide range of older people including those who do not have confirmed low muscle mass . Considering this and the less strong and consistent associations of muscle mass with future health outcomes, compared to tests of strength and function, whether muscle mass measurement is necessary in the wider clinical setting warrants debate.
The EWGSOP suggested criteria for low muscle strength and slow walking speed also deserve appraisal. These criteria are based on a report from a population-based study in Italy (n=1,020; age 20-85+ years) . However, these cut-off points may not be suitable for all populations, considering differences in absolute physical capability levels reported between populations of different countries [46, 47] even when part of the same study .
It is also possible that levels of physical capability reported here are unusually high or unusually low, limiting our ability to assess the potential impact of applying the EWGSOP algorithm. Other UK and European population-based studies reporting physical capability levels are summarised in Additional file 4: Tables S1 and S2. On average participants in our study walked more quickly than participants from other UK cohorts but were similar in terms of grip strength, particularly to participants from the English Longitudinal Study of Ageing (ELSA). With respect to the faster usual walking speed in our cohort, it could be that selective attrition of participants with poorer health, during the 20 years of follow-up, has resulted in a sample less representative of the general population than the cohort at baseline . However, absolute physical capability levels are difficult to compare between studies, due to differences in measurement protocols [48, 49]. Overcoming this barrier, we measured grip strength using the same dynamometer and protocol to ELSA, whose participants were originally enrolled in the Health Survey for England. Therefore, when using comparable measurement protocols, the physical capability of our cohort is similar to a nationally representative sample.
The EPIC-Norfolk study and measurements taken at the 3HC have some limitations. Associations between age and physical capability are explored using cross-sectional data. Thus, we cannot be certain that we are examining age-related changes in physical capability. Additionally, strength and performance measures were not reported in all participants and data was more likely to be missing in older, female participants. This bias could explain the tapering of the gender gap in maximum grip strength with advancing age. Against this is the relatively low volume of missing data for grip strength (1.7%) and the considerable attenuation of the age-sex interaction when the relative change in grip strength was calculated.
Nevertheless, EPIC-Norfolk 3 comprises a large number of participants from the general population at baseline, with a wide age-range across both sexes. Participants have been examined under standardised conditions by trained research nurses using validated measurement techniques to examine a comprehensive range of physical capability measures. Additionally, any truncation of the cohort due to selective attrition of the frailest members is likely to make some of our findings an underestimation.