PMC:4159490 / 25974-34368 JSONTXT

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Our accelerometer measured daily physical activity and the three physical performance tests appear to be reliable and reproducible [21, 23]. The 6-MWT and sit-to-stand test rather objectively monitor progress after exercise training in MHD patients [23]. However, after adjustment for age, gender, and diabetes, our study demonstrated a significant association only between daily physical activity and 6-MWT but not sit-to stand or stair climbing (Table 4). Maximum activity and adjusted activity human activity profile scores correlated with daily physical activity in unadjusted but not adjusted analyses. However, the human activity profile maximum activity and adjusted activity scores were highly significantly correlated, both before and after adjustment, with each of the three physical performance tests (Table 4, Figs. 3 and 4). These findings support the contention that the human activity profile gives a more reliable assessment of physical performance or exercise capability than it does of daily physical activity [20, 24].\nThe rather weak correlation between daily physical activity, determined by the activity monitor, and the physical performance tests is consistent with other studies in older men (≥65 years old) [25], and suggest that factors in addition to physical capability also play a role in determining daily physical activity. The fact that the MHD patients in this study were a relatively healthy subgroup and that more severely debilitated MHD patients were excluded from study may also explain the rather weak correlations between daily physical activity and physical performance that were observed in the present study; i.e., if the ranges of daily physical activity and physical performance scores among the MHD patients were greater, the correlations between these two variables might have been more statistically significant.\nPhysical inactivity and increased time at bed rest are commonly observed in MHD patients [7, 10, 26]. Decreased physical activity can lead to detrimental effects on the heart and musculoskeletal system, result in profound reductions in physical work capacity, and aggravate such comorbid states in dialysis patients as cardiac dysfunction, skeletal muscle wasting, glucose intolerance, and reduced bone density [26]. High daily physical activity levels are associated with beneficial clinical traits in both chronic kidney disease patients and the general population. Higher usual physical activity levels, determined by questionnaires are associated with better nutritional status [5, 6], less inflammation [6], and an increased employment rate in incident dialysis patients [27]. Increased physical activity in MHD patients is associated with less sleep disturbances [28, 29], and improved nutritional status and body composition [5, 8, 30, 31]. The amount of time spent in increased physical activity was significantly associated with greater walking ability, improved physical fitness, and better quality of life in MHD patients [32]. As with our findings, in older men, usual physical activity correlated with exercise capacity [33]. By contrast, low daily physical activity is associated with increased hospitalizations and mortality in MHD patients [4, 15, 34, 35], greater mortality in stage 2–4 chronic kidney disease patients [36, 37], increased risk of cardiovascular and all-cause mortality in renal transplant recipients [2], increased cancer-related mortality and all-cause mortality in cancer patients [38, 39], and increased mortality in older people [40].\nWhile the association between physical performance and morbidity or mortality outcomes has not been directly investigated in MHD patients, several studies have used the SF-36 questionnaire Physical Component Score as a proxy for physical performance. The Physical Component Score is based largely on questionnaire items determining the extent to which patients are “limited” in performing common physical tasks of varying difficulty. In two studies, MHD patients with low Physical Component Scores had greater hospitalization or mortality risks [14, 41]. Johansen et al. reported that lower adjusted human activity profile maximum activity and adjusted activity scores were associated with increased mortality in 1,054 ambulatory MHD patients [42].\nOur findings of reduced daily physical activity and physical performance may be particularly relevant because we studied an apparently healthier subgroup of MHD patients. This would suggest that renal failure and possibly, treatment regimens for renal failure per se may reduce daily physical activity and physical performance. Evidence that we studied healthier MHD patients includes the following: (1) Our inclusion/exclusion criteria precluded many comorbid conditions and stipulated that patients were not recently hospitalized, except for vascular access repair, and were able to perform the 6-MWT. (2) The patients’ serum albumin averaged 4.1 g/dL, which was the same as our normal control values and substantially higher than is reported in large epidemiological studies of MHD patients [43]. (3) Their BMI, LBM, percent body fat, and body weight were within the healthy range (Table 1). (4) Patients’ normalized protein nitrogen appearance (nPNA) was 1.10 ± 0.26 g protein/kg/day, which is greater than that reported for most MHD patients [27–29]. nPNA somewhat underestimates the daily dietary protein intake [44], and this value is only slightly lower or not different from protein intake recommended for MHD patients by K/DOQI and other expert workgroups [45, 46]. Moreover, MHD patients who describe good appetite demonstrate less inflammation and greater survival [47]. (5) The mean Charlson Comorbidity Index value of the 72 MHD patients was 5.7 ± 2.7 with a median value of 5, which is not high for dialysis patients [19, 48, 49]. (6) Daily physical activity and physical performance in our non-diabetic MHD patients, when analyzed separately, are still substantially and significantly decreased compared to normal adults (unpublished data).\nThis study does not indicate whether low daily physical activity and reduced physical performance in our MHD patients were causally related to each other. Moreover, it does not indicate whether increasing DPA will improve physical performance or whether greater exercise training to increase physical performance will enhance DPA. It would not be unlikely that low daily physical activity and reduced physical performance may each contribute to the other disorder in MHD patients.\nThis study has several limitations; first, the activity monitor was worn on the hip, which might limit its ability to detect upper body movements. Second, the sampling of different racial and ethnic groups was limited, and this study was focused on relatively healthy non-diabetic and diabetic MHD patients. Among the strengths of this study, very few other studies have examined relationships between daily physical activity and physical performance in MHD patients. This study is one of the few that used an instrument to measure daily activity. Our sample size of MHD patients was rather large. Since relatively healthy MHD patients were studied, we were able, to some extent, to separate the effects of end-stage kidney disease and MHD treatment on daily physical activity and physical performance from other common comorbid conditions that afflict MHD patients, such as protein-energy wasting, severe heart disease, strokes, amputations, or emotional depression.\nIn summary, this study confirms and extends previous findings of major reductions in daily physical activity and physical performance in MHD patients. In MHD patients, increased physical activity and physical performance, usually determined by questionnaires, are associated with improved outcomes [2, 6, 8, 14, 15]. Since physical performance is associated with daily physical activity and can be improved with exercise training in MHD patients [50–52], exercise might also improve daily physical activity. Research is clearly indicated to examine how to best increase physical performance and daily physical activity in MHD patients and to ascertain whether such strategies will improve their clinical outcomes."}