LAUSR

ABSTRACT Introduction Chronic kidney disease (CKD) patients have a high degree of fatigue relating to neuromuscular symptoms. There is a lack of evidence regarding the etiology of neuromuscular fatigability in elderly CKD patients. Methods Inclusion criteria are as follows: age ≥60 yr, glomerular filtration rate (GFR) <45 mL·min−1 per 1.73 m2 in CKD patients, and GFR >60 mL·min−1·1.73 m−2 in controls. The fatigability protocol consisted in a submaximal handgrip task at 40% peak force. Fatigue was assessed using the Multidimensional Fatigue Inventory–20 items (MFI-20) and the Functional Assessment of Chronic Illness Therapy–Fatigue questionnaires. Peak rate of force development (RFDpeak, normalized: NRFDpeak) and rate of EMG rise (RER) were measured during explosive contractions; peak force and mean surface EMG were measured during maximum voluntary contractions. Multilevel models tested neuromuscular parameters adjusted for clinical and Multidimensional Fatigue Inventory–20 items subscales. Neuromuscular fatigability contribution to fatigue description was tested using model comparison. Results The study included 102 participants; 45 CKD patients and 57 controls. CKD mainly affected the mental and the reduced motivation subscales of fatigue. CKD was associated with greater neuromuscular fatigability assessed using NRFDpeak (group–time interaction, −16.7 % MVF·s−1, P = 0.024), which increased with fatigue severity (P = 0.018) and with a higher rate of decrement in RER compared with controls (RER at 50 ms: β = −121.2 μV·s−1, P = 0.016, and β = −48.5 μV·s−1, P = 0.196, respectively). Furthermore, these patients show an association between the reduced motivation subscale and the RER (e.g., 30 ms: β = −59.8% EMGpeak·s−1, P < 0.001). Only peak force fatigability contributed to fatigue variance, whereas RFDpeak did not. Conclusions In CKD patients, the neuromuscular fatigability assessed using RFDpeak is related to an impairment in motor-unit recruitment or discharge rates, whereas only peak force fatigability was related to fatigue. This suggests that targeting exercise interventions might lessen fatigue and improve quality of life in CKD patients.