Effects of endurance training on extrarenal potassium regulation and exercise performance in patients on haemodialysis

Background. Haemodialysis patients (HDP) with anaemia display impaired plasma K+ regulation during exercise and poor exercise performance. Epoetin treatment and exercise training improve exercise performance in HDP, but whether this is associated with improved K+ regulation is unknown. Methods. Six HDP with near-normal [Hb] were tested for aerobic power ((V) over dot O-2peak) and plasma [K+] during incremental exercise; quadriceps muscle strength (peak torque, PT) from 0 to 360 degrees s(-1) and fatiguability (decline in strength during thirty contractions). Tests were conducted at baseline, after 6 weeks of normal activity (pre-train) and following 6 weeks cycle training (post-train). Six healthy untrained controls (CON) matched for age, sex, mass and height were tested at baseline. Results. In HDP at baseline, (V) over dot O-2peak and PT from 0 to 360 degrees s(-1) were respectively reduced by 37% and 27-42%, compared to CON (P < 0.05). Plasma [K+], the rise in [K+] (Delta[K+]) and the Delta[K+] relative to total work done (Delta[K+] work(-1) ratio) during incremental exercise were all higher in HDP at baseline compared to CON (P < 0.05). Exercise training increased time to fatigue by 12% (P < 0.05) but did not improve K+ regulation or (V) over dot O-2peak. An inverse correlation was found between the Delta[K+] work(-1) ratio and (V) over dot O-2peak for pooled CON and HDP data. Conclusions. In HDP treated with epoetin, poor exercise performance was related to impaired extrarenal K+ regulation, whilst training improved exercise performance but not K+ regulation. Thus, although impaired extrarenal K+ regulation may contribute to poor exercise performance in HDP, exercise performance can still improve with training despite unchanged K+ regulation.