Neuromuscular And Functional Performance In Individuals With Chronic Kidney Disease Compared To Healthy Controls

Reductions in rate of force development (RFD) and maximal strength in individuals with chronic kidney disease (CKD) may be due to altered motor unit recruitment strategies. PURPOSE: Assess differences in neuromuscular and functional performance in individuals with CKD (stages 3b - 5) compared to healthy controls. METHODS: Thirty-four people with CKD stage 3 (CKD3; n = 10), CKD stage 4 (CKD4; n = 9), or CKD stage 5 (CKD5; n = 5), or apparently healthy controls (HC; n = 10) were recruited to participate. Visit 1 consisted of isometric familiarization and six-minute walk (SMW) tests. Visit 2 consisted of maximal isometric knee extension force (MVIC) followed by submaximal isometric ramp contractions at 30% and 70% MVIC. Surface electromyography was recorded from the right vastus lateralis during submaximal ramp contractions and decomposed into its motor unit action potential trains. Linear slope coefficients (slope) and y-intercepts (y-int) of the mean firing rate vs. recruitment threshold regression at each submaximal intensity were used for analysis. RFD was assessed at 50, 100, and 200 ms relative to force onset. Group differences for 6 MW, MVIC, RFD50, RFD100, and RFD200 were assessed via one-way ANOVA. Exploratory analyses for the 30% and 70% MVIC slope and y-int were conducted using Hedges g effect size with 95% confidence intervals. RESULTS: An effect of group was observed for 6 MW (p < 0.001). Follow-up analysis indicated significantly lower 6 MW distance in CKD4 (p < 0.001) and CKD5 (p = 0.006) compared to HC. No significant effect of group was observed for MVIC (p = 0.070), RFD50 (p = 0.082), RFD100 (p = 0.168), or RFD200 (p = 0.196). A large effect was observed indicating higher y-int at 70% MVIC in CKD compared to HC (g = 1.391 [0.55, 2.23]). A moderate effect was observed indicating a lower slope at 30% MVIC in CKD compared to HC (g = -0.463 [-1.24, 0.31]). All other effects for motor unit comparisons were negligible (-0.124 ≥ g ≥ 0). CONCLUSIONS: Individuals with CKD experience progressive losses in functional performance compared to HC. Differences in MVIC and RFD were not observed, but a large effect was observed for faster motor unit firing at the same intensity in CKD. Future research should explore effects of lifestyle and body composition on strength preservation despite loss of functional performance in CKD.