NPPB and myalgic encephalomeyelitis/chronic fatigue syndrome: The maximum achieved load was negatively correlated with the BNP (r = −0.424, P < 0.001), 5-STS (r = −0.573, P < 0.001), CFS (r = −0.496, P < 0.001), and SARC-F (r = −0.600, P < 0.001) scores, while a positive correlation was observed with grip strength (r = 0.672, P < 0.001).