Nutritional support or exercise training is associated with an increase in serum albumin and pre-albumin [1]. The serum albumin concentration is a crucial dialysis-related nutritional factor that reflects protein-energy wasting, muscle strength, and physical function in connection with intradialytic exercise training [2,4,5]. However, there is insufficient evidence of intradialytic aerobic exercise combined with nutritional factors to improve body composition parameters [5]. Therefore, this study hypothesized that an intradialytic aerobic exercise program combined with the nutritional factor of the serum albumin concentration affects frailty, dialysis adequacy, body composition parameters, and QoL among hemodialysis patients. The exercise group completed a 12-week program of intradialytic aerobic exercise and a single education session (n = 18), whereas the control group completed only the education session (n = 21). The serum albumin value was classified as low level (≤3.8 g/dL), or normal level (>3.8 g/dL) based on previous reports that low serum albumin (cutoff value of 3.8 g/dL) reflects protein-energy wasting that is concomitant with low body mass index, reduced muscle mass, and unintentional low dietary intake [6]. Moreover, it is evident that serum albumin higher than 3.8 g/dL is associated with a greater increase in renal urea clearance, normalized protein catabolic rate, lower mortality, and reduced cardiovascular death among hemodialysis patients [7,8]. In this study, the mean albumin value was 3.82 ± 0.38 g/dL. Cases of low albumin levels in the exercise and control groups were 50.0% (n = 9) and 57.1% (n = 12), respectively (χ² = 0.20, p = 0.75). Although there was no significant difference in the baseline mean albumin value between the exercise and control groups (3.87 ± 0.18 g/dL vs. 3.77 ± 0.49 g/dL, t = 0.92, p = 0.37), the frailty score classified exercise and albumin level had a significant difference (p = 0.02) (Table 1). As we did not achieve selection balance, the dialysis vintage [4] and baseline frailty score should be considered confounding variables to determine the interaction effects. There was a significant interaction between groups and albumin levels in dialysis efficacy at week 12 (p = 0.02). The exercise group with albumin >3.8 g/dL exhibited the highest Kt/V of 1.88 ± 0.32 with a large effect size (f = 0.41) among the four subgroups (Table 1). The two-way analysis of covariance for changes in frailty, Kt/V, short physical performance battery score, body composition profiles, and QoL revealed that the exercise group with albumin>3.8 g/dL exhibited a significant improvement in the short physical performance battery score of 1.67 (p = 0.05) with a moderately high effect (f = 0.35) (Table 2). The change in lower leg muscle mass in the albumin >3.8 g/dL group was significantly lower than that in the albumin ≤3.8 g/dL group (p = 0.02) (Table 2).

This study did not find any significant interaction between exercise training and serum albumin levels with regard to an improvement in body composition profiles. Additional research is needed to determine whether aerobic exercise with various sessions, durations, and intensities, or nutritional support might be useful for improving body composition profiles in hemodialysis patients. The present study had several limitations that warrant consideration. First, we included only patients undergoing treatment at a single hemodialysis center, and the results might not be generalizable to other centers and patient populations [4]. Second, the small sample size could indicate a risk of bias to use of factorial statistics for the exercise and nutritional factors. Lastly, because the effects of intradialytic aerobic exercise on body composition have been controversial, this discrepancy should be verified through further research by modifying the duration, time, and intensity of the intradialytic aerobic exercise program and nutritional support program in a larger, multicenter population.