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Peak oxygen uptake correlates with indices of sarcopenia, frailty, and cachexia in older Japanese outpatients

Peak oxygen uptake (peak VO2) is known not only as an index of aerobic fitness but also one of an index of life expectancy. Frailty, sarcopenia, and cachexia are associated with a poor prognosis and high mortality. The purpose of this study was to determine the relationships of peak VO2 with the features of sarcopenia, frailty, and cachexia, to provide insight into which might mediate the poor prognosis.


Introduction
Peak oxygen uptake (peak VO 2 ) is a function of oxygen delivery (cardiac output, haemoglobin, etc.) and oxygen utilization (muscle volume and function, etc.) and is influenced by ventilation, cardiac function, vascular function, and muscle function, in other words, respiration, circulation, and metabolism. 1 It is known that the most reliable and powerful prognostic index, not only for cardiac patients 2,3 but also for the general population, 4 is exercise tolerance (i.e. peak VO 2 ). 1 Sarcopenia, 5 frailty 6 (including cognitive and psychological frailty 7,8 ), and cachexia 9 have received significant attention in recent years. It is known that sarcopenia may develop prior to frailty (i.e. age-related sarcopenia 10 ) and represents one component of frailty. 6,11 Furthermore, it has recently been shown that sarcopenia is strongly associated with cardiovascular mortality and all-cause mortality. 12,13 Physical frailty is not only an indicator of pre-disability but also a predictor of hospitalization, cardiovascular disease, and mortality. 14 In addition, cognitive and psychological frailty 7,8 are also associated with adverse health outcomes and death among physically frail people. 15,16 Cachexia (including cardiac cachexia) has been shown to overlap with sarcopenia, and indeed, the patients may represent a subset of patients with sarcopenia (cachexia-related sarcopenia), 10,17,18,19 which is associated with high mortality. 20 Thus, all of these three states are associated with poor prognosis and/or mortality.
Although linear relationships have previously been demonstrated between peak VO 2 and sarcopenia, frailty, and cachexia, 21 the relationships between peak VO 2 and the various features of sarcopenia, frailty, and cachexia remain to be established.
Clarification the relationships between peak VO 2 and the various features of sarcopenia, frailty, and cachexia might be useful to insight into why peak VO 2 are reliable and powerful prognostic index among not only for cardiac patients 2,3 but also for the general population. 4 Therefore, we first aimed to investigate the relationship between peak VO 2 and the features of sarcopenia, frailty, and cachexia in a group of older community-dwelling Japanese participants, and second, to validate these relationships using a second group of participants. In addition, because there have been only one study of peak VO 2 in community-dwelling older Japanese adults, 1 we also aimed to determine the relationship between peak VO 2 and age in these groups. In this study, we used the features of sarcopenia, frailty, and cachexia identified by the Asian Working Group for Sarcopenia criteria, 22 the Japanese version of the Cardiovascular Health Study, 23 and 'Cachexia: A new definition'. 9

Participants
The participants were 175 older community-dwelling adults (58 men and 117 women) who lived in the Tokyo metropolitan area. The mean age of the participants was 77.6 years (range 65-97 years). None of the participants were hospitalized at the time of the study, but all of them were receiving outpatient treatment at our hospital. The exclusion criteria were: age < 65 years, impaired vision, impaired hearing, musculoskeletal impairment that might interfere with the ability to perform the symptom-limited exercise test, and any clinically unstable condition. Potential participants who habitually performed exercise training were also excluded from the study. Habitual exercise training was defined as the performance of a repetitive activity more than three times a week, for the purpose of improving and/or maintaining physical performance, and included aerobic training (walking or swimming), resistance training, or a combination of these methods (cycling). The participants' clinical characteristics are summarized in Tables 1 and 2. We have previously reported the clinical characteristics of this group of participants after they had been allocated to five groups: robust, pre-frail, sarcopenic, frail and cachexic. 21 Participants were classified into robust, pre-frail, frail, sarcopenia, or cachexia groups using the following method. First, we counted the number of participants with cachexia. After excluding those with cachexia, we counted the number of participants with frailty. Next, after excluding those with cachexia and frailty, we counted the number of participants with sarcopenia, according to the report 'From sarcopenia to frailty' by Fried et al. 6 and Morley et al. 6,11 After excluding participants with cachexia, frailty, and sarcopenia, we counted the number of participants who were pre-frail. Finally, after excluding those with cachexia, frailty, sarcopenia, and pre-frailty, the remaining participants were considered robust. 21 Of the 175 community dwelling older adults, 17% (n = 30) were robust, 40% (n = 70) were pre-frail, 12% (n = 21) were sarcopenia, 25% (n = 44) had frail, and 6% (n = 10) had cachexia. 21 The number of participants with overlapping states based on the original definitions as follows: of 10 participants in the cachexia group, two were also classified as sarcopenia and pre-frail, one as frail, and seven as sarcopenia and frail. Of the 44 participants in the frail group, 32 were also classified as frail and 12 as sarcopenia. All 21 participants in the sarcopenia group were classified with overlapping prefrailty. Of all participants (n = 175), the prevalence rates of overlapping states were 17% (n = 30) for robust, 53% (n = 93) for pre-frailty, 24% (n = 42) for sarcopenia, 30% (n = 52) for frailty, and 6% (n = 10) for cachexia. 21 To confirm the validity of the peak VO 2 prediction formula obtained, the same tests were conducted in another group of participants [32 men and 130 women; mean age 77.3 ± 5.5 years (range 65-96 years)], who were consecutively recruited using the same inclusion and exclusion criteria.

Laboratory assays
All the participants had fasting blood samples drawn from a large antecubital vein to determine haemoglobin concentration (Hb), red cell distribution width (RDW), serum albumin, and high-sensitivity C-reactive protein concentration. Hb and RDW were analysed using a Sysmex XE-5000 automated haematology system (Sysmex Corporation, Hyogo, Japan), serum albumin was analysed using the bromocresol purple assay (Shino-Test Corporation, Tokyo, Japan), and highsensitivity C-reactive protein concentration was analysed using the CRP-Latex (II) immunoturbidimetric assay (Denka Seiken Corporation, Tokyo, Japan).

Skeletal muscle mass index, total body fat mass index, and body mass index
Appendicular skeletal muscle mass was measured using total body dual-energy X-ray absorptiometry (Lunar iDXA, GE Healthcare, Tokyo, Japan). The sum of the muscle mass of the four limbs was considered to be the appendicular skeletal

Physical performance evaluation
To determine their usual walking speed (u-WS; m/s), we asked participants to walk along a straight 11-m walkway on a flat floor, once, at their usual speed. Walking speed was measured over a 5 m distance between markers placed 3 and 8 m from the start of the walkway. Two trials were conducted per person, with the shorter time being used in the analyses.
Hand grip strength (HGS) is a valid indicator of overall muscle strength, and it is a particularly useful indicator of upper-extremity strength. HGS was assessed twice for each hand, alternately, using a Smedley-type JAMAR hand dynamometer (Sammons Preston Rolyan, Bolingbrook, IL, USA). The highest value obtained was used in the analyses.
All the physical performance parameters were assessed for each participant by trained research assistants.

Assessment of weight loss, exhaustion, physical activity, and anorexia
According to the Japanese version of the Cardiovascular Health Study, 23 weight loss was assessed by a response of 'yes' to the question, 'Have you lost 2 kg or more in the past six months?', 23 and exhaustion was considered to be present if the participant responded with 'yes' to the following questions: 'In the last two weeks, have you felt tired for no reason? ' We evaluated the role of physical activity by asking the following questions about time spent engaged in sports and exercise: (i) 'Do you engage in moderate levels of physical exercise or sports aimed at health?' and (ii) 'Do you engage in low levels of physical exercise aimed at health?' Participants who answered 'no' to both of these questions were classified as low activity. 23 Anorexia was defined to be present if the participant responded with 'very poor' and 'poor' to following questions: 'My appetite is' a. very poor, b. poor, c. average, d. good, and e. very good. 24

Assessment of cognitive function and depression
The Montreal Cognitive Assessment (MoCA) is a screening tool that has been validated in many different countries, including Japan (MoCA-J). 25 It is normally used in the clinical setting for the detection of mild cognitive impairment or early dementia in older adults. The range of scores obtained is 0-30, with higher scores indicating better cognitive performance. The MoCA-J was selected as the main cognitive test, because of its greater sensitivity for the detection of mild cognitive impairment in community-dwelling people than the Mini-Mental State Examination. 25 Depression status was assessed using the Geriatric Depression Scale-15 (GDS-15), 26 which is a commonly used instrument for depression screening in the general geriatric population. The GDS-15 is a questionnaire that does not focus on somatic symptoms or contain any questions about suicide. All 15 items are scored as either 0 or 1, and the total score ranges from 0 to 15. Scores from 5 to 9 indicate a minor depressive disorder and scores ≥ 10 indicate a major depressive disorder.
Trained research assistants assessed each participant's cognitive function and depression status.

Echocardiography
All the participants underwent transthoracic echocardiography using an echocardiograph equipped with a broadband transducer (Vivid E9®, GE Healthcare, Tokyo, Japan). Measurements for the left ventricle were obtained from the parasternal long-axis and apical four-chamber views, in accordance with standard criteria. Left ventricular ejection fraction (EF) was automatically calculated using the modified Simpson rule in the apical two-chamber and four-chamber views. We categorized the results into reduced EF (<40%), mid-range EF (40-49%), and preserved EF (≥50%), according to the 2016 guidelines of the European Society of Cardiology for the diagnosis and treatment of acute and chronic heart failure. 27

Cardiopulmonary exercise test
All participants underwent a symptom-limited bicycle ergometer cardiopulmonary exercise test (CPET) using an upright, electromagnetically braked cycle ergometer (Aerobike Strength Ergo-8; Mitsubishi Electric Corporation, Tokyo, Japan), a metabolic analyser (Aero Monitor AE-310S; Minato Medical Science Company Limited, Osaka, Japan), and electrocardiography (ML-9000 stress test system; Fukuda Denshi Company Limited, Tokyo, Japan). The exercise test began with a 3 min rest on the ergometer, which was followed by a 4 min warm-up at 0 watt (W) at 60 rpm. The load was then increased incrementally by 15 W/min. All the CPET parameters were measured from the beginning of the initial rest period on the cycle ergometer until the end of the exercise session.
The CPET was terminated on the participant's request, if abnormal physiologic responses occurred, 28 or if the participant was unable to continue to perform the exercise correctly. The VO 2 obtained was smoothed using an eight-breath moving average. Peak VO 2 was defined as the highest VO 2 value obtained during the last minute of the CPET. When the respiratory exchange ratio [carbon dioxide uptake/oxygen uptake (VCO 2 /VO 2 )] was <1.0 at peak exercise, the test was considered inadequate, because of poor effort, and the peak exercise data were not used in the analyses. In the present study, we used peak VO 2 (mL/min), rather than peak VO 2 /body mass (mL/min/kg), because we wished to determine the relationship between peak VO 2 and sarcopenia, frailty, and cachexia-related factors, which include BMI and SMI.
Pearson's correlation analysis was performed to determine the relationship between peak VO 2 and biochemical parameters or physiologic assessments, and Spearman's correlation analysis was performed to determine the relationship between peak VO 2 and MoCA-J score or GDS-15 score. Multiple linear regression analysis were used to predict peak VO 2 and were adjusted for age, sex, Hb, SMI, total body fat mass index, HGS, u-WS, MoCA-J score, GDS-15 score, fatiguability, anorexia, low physical activity in daily life, hypertension, dyslipidaemia, diabetes mellitus, atrial fibrillation, chronic heart failure, chronic kidney disease, cancer, and red cell width distribution.
Pearson's correlation analysis was used to determine the relationship between peak VO 2 , measured using CPET, and the predicted peak VO 2 in a second group of 162 consecutively recruited participants. To determine the relationship between age and peak VO 2 in both groups, comprising 337 older people, we performed Pearson's correlation analysis.
All the statistical analyses were performed using IBM SPSS Statistics for Windows, Version 22.0 (IBM Corporation, Armonk, NY, USA). The significance level was set at P = 0.05 for all the tests.

Ethical considerations
This study was approved by the Ethics Committee of our hospital (Authorization Number: 240301) and conformed with the principles outlined in the Declaration of Helsinki and its amendments. All participants gave their written informed consent before data collection.

Results
The clinical characteristics of the participants are summarized in Tables 1 and 2. The correlations between peak VO 2 and biochemical, physiologic, physical, cognitive, and psychological parameters are shown in Table 3. There were significant correlations between peak VO 2 and age, BMI, Hb, RDW, serum albumin, SMI, total body fat mass index, HGS, u-WS, MoCA-J score, and GDS-15 score, but not with high-sensitivity C-reactive protein (Table 3 and Supporting Information, Data S1). Table 4 shows the results of the multiple linear regression analyses. These showed that age (B = À11.6, P < 0. We used the outputs of the multiple linear regression analyses to create a formula for the prediction of peak VO 2 (mL/min). This was predicted peak VO 2 (mL/min) = À11.6 × age (years) + 25.5 × Hb (g/dL) + 114.2 × SMI (kg/m 2 ) + 8.9 × HGS (kg) + 226.4 × u-WS (m/s) À 65.8 × fatiguability (absence 0, presence 1) À 177.4 × CHF (absence 0, presence 1) + 437.1. We then tested the validity of the formula using the second group of participants and found a significant correlation (r = 0.78, P < 0.001) between the peak VO 2 (mL/min), measured using CPET, and the peak VO 2 (mL/min) predicted using the formula (Figure 1).
In the combined group of 337 older people, there was a significant relationship (r = À0.46, P < 0.001) between age and peak VO 2 ( Figure 2).

Discussion
Our study used data from consecutively recruited, older outpatients attending a geriatric clinic who lived in the Tokyo metropolitan area. The first aim of this study was to determine the relationships between peak VO 2 and multiple features of sarcopenia, frailty, and cachexia. Although sarcopenia, frailty, and cachexia may be prevented and/or reversed by exercise training, [29][30][31][32] previous studies have used mortality as an outcome. [33][34][35] However, peak VO 2 , a bi-directionally changeable index, might be one of the useful outcome. Therefore, clarification of the relationships between peak VO 2 and the features of sarcopenia, frailty, and cachexia might provide important insights into which factors that are closely related to poor prognosis and which factors are important to reverse these syndromes by intervention.
We have shown that peak VO 2 is independently associated with age, Hb, physical function (SMI, HGS, & u-WS), fatiguability, and CHF (Table 4). Although relationships between peak VO 2 and indexes such as age, 1,36 anaemia, 37 SMI, 38 HGS, 39 u-WS, 40 fatiguability, 41 and CHF 42 have previously been reported, no previous studies have investigated the relationship between peak VO 2 and this cluster of sarcopenia, frailty, and cachexia-related factors.
Peak VO 2 is a function of oxygen delivery (cardiac output, haemoglobin, etc.) and oxygen utilization (muscle volume and function, etc.) and is influenced by ventilation, cardiac function, vascular function, and muscle function, in other words, respiration, circulation, and metabolism. 1 Although there have been many studies showing that peak VO 2 decreases with age, 1,36 and the relationship between peak VO 2 and age has been reported in healthy Japanese individuals aged 20-78 years, 1 there have been no studies of the relationship between peak VO 2 and age in community-dwelling Japanese adults of ≧65 years. In the present study, we have shown a significant relationship between peak VO 2 and age in 337 adults aged 65-97 years (Figure 2), although this was not strong (r = À0.46). This is likely to be because the decline in peak VO 2 is determined not only by age but also by changes in body composition and power. 36 We have previously reported associations between peak VO 2 and SMI, and peak VO 2 and HGS, which we suggested might be underpinned by the degradation of sarcomeric proteins in both skeletal muscle and cardiomyocytes via the   ubiquitin-proteasome system 38 . 39 Coen et al. has reported that walking speed is affected by muscle mitochondrial efficiency and peak VO 2 , 40 and Otto et al. showed in a multicentre study that lower peak VO 2 is independently associated with lower Hb concentration, implying that poorer exercise performance may be due to lower oxygen-carrying capacity. 37 In addition, Malhotra et al. reported that peak VO 2 is an important prognosis indicator, not only in heart failure with low left ventricular EF, but also in cases with preserved left ventricular EF. 42 Finally, De Becker et al.
reported that when compared with sedentary healthy controls, patients with chronic fatigue syndrome had significantly lower peak VO 2 , because of loss of muscle protein, muscle weakness, cytokine abnormalities, and slower protein synthesis. 41 Although there were significant relationships between peak VO 2 and MoCA-J and GDS-15 scores (Table 3), no independent relationships were identified in multiple regression analysis (Table 4). Previously, it was reported that higher VO 2 max is associated with better global cognitive function 43,44 and low VO 2 max is associated with more severe depressive symptoms. 45 However, no relationship was previously identified between fatiguability and cognitive function and depression in frail older individuals. 46 It is more intuitive that fatiguability (a symptom of physical frailty) is likely to be more closely associated with peak VO 2 , a physical index of exercise tolerance, than cognitive function and depression (cognitive and psychological frailty), because fatiguability is a physical symptom that develops because of loss of muscle protein, muscle weakness, cytokine abnormalities, and lower protein synthesis. 41 Additionally, although RDW, which has been widely studied by heart failure researchers, is known not only as a marker of exercise intolerance (i.e. peak VO 2 ) in patients with CHF 47 but also as a strong and independent risk factor for death in the general population, 48 the present findings show that RDW is not an independent marker of peak VO 2 in community-dwelling older people.
In general, peak VO 2 is calculated using the Fick principle: Peak VO 2 = Stroke Volume × Heart rate × arterial-venous oxygen difference (AVO 2 diff). 38 It is known that the most reliable and powerful prognostic index, not only for cardiac patients 2,3 but also for the general population, 4 is exercise tolerance (i.e. peak VO 2 ). 1 Indeed, it was known that 'Each 1-MET (i.e. VO 2 of approximately 3.5 ml per kilogram of body weight per minute) increase in exercise capacity conferred a 12 percent improvement in survival among men' 4 and 'The Framingham Risk Score-adjusted mortality risk decreased by 17% for every 1-MET increase, among women'. 49 However, it is remain unknown why peak VO 2 are reliable and powerful prognostic index in general population. The present findings, from another point of view of Fick principle, suggest mechanisms for how sarcopenia, age-related sarcopenia, 10 and cachexia-related sarcopenia 10,17-19 related with peak VO 2 among community-dwelling older general population.
Thus, clarified the relationships between peak VO 2 and the various features of sarcopenia, frailty, and cachexia in this study, might be useful to insight into why peak VO 2 are reliable and powerful prognostic index among general population.
Although we have previously demonstrated relationships of sarcopenia, frailty, and cachexia with age, BMI, and peak VO 2 , 21 the evaluation of peakVO 2 in older adults is sometimes challenging; therefore, this reliable and novelty formula for the prediction of peak VO 2 , with non-invasive and not under stress, may be useful clinically.
There were several limitations to this study. Firstly, the study was confined to Japanese adults in one geographical location. Further multicentre studies should investigate whether the formula for the prediction of peak VO 2 is suitable for use with other Japanese populations and other ethnicities. Secondly, the participants were recruited in a clinic caring for patients with chronic diseases; therefore, the results may not be applicable to high active elderly peoples such as senior long distance runners and athletes. Thirdly, we did not measure interleukin-6, which is an important mediator of cachexia. 9 Fourthly, the sample size was small to investigate after divided into both of sex. It needs to investigate sex specificity with larger sample. Further research is needed to improve the accuracy of the generated formula and to determine whether SMI, measured using bio-impedance, is a useful inclusion. Additionally, activity is considered to be an important factor that affects VO 2 , but in this study, the relationship with VO 2 was not clarified because the activity was investigated by questionnaire. Further research is needed to clarify the relationship between VO 2 and activity using with activity metre. In the future, the relationship between the changes in peak VO 2 and the changes in the features of sarcopenia, frailty, and cachexia should be studied longitudinally, to provide further insight into the features that would be most effective to target therapeutically to improve life expectancy.
In conclusion, the present study has shown that peak VO 2 is associated with features of sarcopenia, frailty, and cachexia (age, Hb, SMI, HGS, u-WS, the symptom of fatiguability, and CHF) in community-dwelling older adults.

Funding
This research did not receive any funding from agencies in the public, commercial, or not-for-profit sectors.

Author contributions
Masamitsu Sugie, Tetsuya Takahashi, and Marina Nara contributed to the acquisition of data and performed the statistical analysis. Kazumasa Harada, Hajime Fujimoto, Shunei Kyo, and Hideki Ito contributed to the interpretation of the data. Masamitsu Sugie, Kazumasa Harada, Tetsuya Takahashi, and Marina Nara wrote each draft of the manuscript. All authors critically reviewed and significantly contributed to the intellectual content of the manuscript. All authors agreed on the final content of the manuscript.