Blood lactate concentrations during rest and exercise in people with Multiple Sclerosis: A systematic review and meta-analysis

•Blood lactate concentration during rest (LactateREST) is significantly higher in people with multiple sclerosis (PwMS) compared to healthy controls (HC), though more research is needed to confirm if it can be used as a biomarker for MS progression.•Lactate concentration during or shortly post-maximum intensity exercise (LactateMAX) is lower in PwMS compared to HC and is lower still in higher EDSS scoring PwMS compared to lower EDSS scoring PwMS, indicating LactateMAX is affected by severity of MS symptoms.•Blood lactate concentration during sub-maximal exercise intensities (LactateSUB−MAX) can be reduced in PwMS following a chronic exercise training intervention for the same or similar power output.•LactateMAX in PwMS can be increased following a chronic exercise training intervention. Multiple Sclerosis (MS) is a chronic disorder which irreversibly damages axons within brain matter. Blood lactate concentration could be a biomarker of MS onset and progression, but no systematic review has yet sought to confirm or dispute the elevation and biomarker potential of blood lactate in people with MS (PwMS) or to consolidate understanding of lactate production during exercise in PwMS. To perform a systematic review and meta-analysis on blood lactate in PwMS during rest and exertion compared to Healthy Controls (HC) and following chronic exercise intervention. A systematic search of six electronic databases (PubMed, CINAHL, Science Direct, Cochrane Library, SPORTDiscus and PEDro) was performed on 10th April 2020. Mean, standard deviation and sample size for lactate measures at rest and during exercise were pooled to determine overall effect size using a random effects model. The 20-point Appraisal tool for Cross-Sectional Studies was utilised to assess study quality and inherent risk of bias. To qualify for inclusion, studies had to include human adults (>18 years) with a confirmed clinical diagnosis of MS, be published in English, have undergone peer review, report absolute blood lactate values for data extraction, and if involving testing during/after exercise, to do so during bilateral exercise methods. 18 studies were qualitatively analysed and 15 studies quantitatively analysed. Outcome data was available for 1986 participants (nMS = 1129). A total of 7 papers tested blood lactate during rest (LactateREST), 7 papers tested during sub-maximal intensity exercise (LactateSUB−MAX), and 8 papers tested during maximal intensity exercise (LactateMAX). Meta analyses