| Summary: | Physical sedentarism is linked to elevated levels of circulating cytokines, whereas exercise upregulates growth-promoting proteins such as brain-derived neurotrophic factor (BDNF). The shift towards a ‘repair’ phenotype could protect against neurodegeneration, especially in diseases such as multiple sclerosis (MS). We investigated whether having higher fitness or participating in an acute bout of maximal exercise would shift the balance of BDNF and interleukin-6 (IL-6) in serum samples of people with progressive MS (<i>n</i> = 14), compared to matched controls (<i>n</i> = 8). Participants performed a maximal graded exercise test on a recumbent stepper, and blood samples were collected at rest and after the test. We assessed walking speed, fatigue, and maximal oxygen consumption (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mstyle displaystyle="true"><mrow><mrow><mover accent="true"><mrow><mi mathvariant="normal">V</mi></mrow><mrow><mo>·</mo></mrow></mover></mrow><msub><mrow><mi mathvariant="normal">O</mi></mrow><mrow><mn>2</mn><mi>max</mi></mrow></msub></mrow></mstyle></semantics></math></inline-formula>). People with MS achieved about 50% lower <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mstyle displaystyle="true"><mrow><mrow><mover accent="true"><mrow><mi mathvariant="normal">V</mi></mrow><mrow><mo>·</mo></mrow></mover></mrow><msub><mrow><mi mathvariant="normal">O</mi></mrow><mrow><mn>2</mn><mi>max</mi></mrow></msub></mrow></mstyle></semantics></math></inline-formula> (<i>p</i> = 0.003) than controls. At rest, there were no differences in BDNF between MS and controls; however, IL-6 was significantly higher in MS. Higher <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mstyle displaystyle="true"><mrow><mrow><mover accent="true"><mrow><mi mathvariant="normal">V</mi></mrow><mrow><mo>·</mo></mrow></mover></mrow><msub><mrow><mi mathvariant="normal">O</mi></mrow><mrow><mn>2</mn><mi>max</mi></mrow></msub></mrow></mstyle></semantics></math></inline-formula> was associated with a shift in BDNF/IL-6 ratio from inflammation to repair (R = 0.7, <i>p</i> = 0.001) when considering both groups together. In the MS group, greater ability to upregulate BDNF was associated with faster walking speed and lower vitality. We present evidence that higher fitness indicates a shift in the balance of blood biomarkers towards a repair phenotype in progressive MS.
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