**8. Aerobic fitness and haematocrit (Hct) normalisation**

Due to an increase in cardiac output and an improvement in muscles' innate ability to receive and use oxygen from the blood, physical activity has inherent benefits [78]. According to a meta-analysis, both moderate and intensive exercise trainings improve cardiorespiratory fitness and cardiometabolic health [79].

Patients with ESRD have a significant loss of fitness and functional competence [80], increasing their risk of death and limiting their ability to carry out everyday tasks [81, 82]. Renal anaemia is one of the most important variables that contribute to poor physical fitness [14]. Anaemia lowers oxygen carrying capacity, posing a barrier to maximum oxygen intake, PE capacity, and time to fatigue, particularly in those with ESRD [83].

Oxygen absorption can be viewed as an avenue for oxygen to get from the lungs to functioning tissues *via* systemic blood released by the heart during PE (physical exercise). Instead of being forced to deal with renal anaemia, recombinant erythropoietin

#### *Effect of Exercise on Health-Related Quality of Life in Patients with End-Stage Renal Disease DOI: http://dx.doi.org/10.5772/intechopen.101133*

was developed. A popular treatment for anaemia is erythropoiesis-stimulating agents (ESAs), which enhance QoL and cognitive function [84, 85], reduce left ventricular hypertrophy [86], and slightly increase maximum oxygen uptake in relation to haematocrit rise when used to treat anaemia [87]. Intradialytic PE, on the other hand, increases maximal oxygen absorption [88, 89] and has a cardioprotective effect [90]. PE, like ESAs, does not restore exercise ability in CKD patients to that of healthy people [24, 91]. Both of these treatments have been proven to improve maximum oxygen uptake and physical fitness, but they do not restore patients' fitness levels to those seen in the majority of sedentary people with normal renal function. Despite the fact that raising the haematocrit increases the blood's oxygen carrying capacity, other parts of the oxygen pathway remain intact, preventing the normalised haematocrit from providing any further health advantages. The ability of regular PE to give its maximal benefit is, on the other hand, restricted by the existence of anaemia. In a third situation, some components of dialysis or ESRD obstruct the regular oxygen pathway, which may be unaffected by either Hct normalisation or regular PE [92].

When compared to the numbers in the untrained anaemic phase, PE, Hct normalisation, or their combination leads in significantly increased maximal power and VO2. PE boosts cardiac output, peak tissue-diffusing capacity, and citrate synthase activity, but Hct normalisation boosts maximum arterial oxygen and arteriovenous oxygen difference. The maximal arteriovenous oxygen difference did not increase even when arterial oxygen levels increased in the combined phase, and they were the same as in healthy sedentary people [93]. As a result, it can be inferred that exercise and Hct normalisation have good effects but do not result in normalisation of exercise capacity in HD patients, which could be due to skeletal muscle anomalies.
