The maximum distance achieved on a modified 12 min walk test (12MWT) is a well-established measure in McArdle disease glycogen storage disease type V (GSDV). Age, height, body mass and gender are known predictors of walking distance in other patient groups. Reference values to correct for these predictors are necessary for comparisons between individuals. To date, there has not been a systematic investigation of these predictors in the 12MWT in GSDV. This study explores the contribution of these predictors on distance achieved in GSDV. Data, included maximum distance walked, age, gender, height and body mass, was collected from 103 GSDV patients who underwent 12MWT between 2011 and 2017. Analysis showed a significant correlation between distance achieved and height, age, body mass and gender. Multiple linear regression analysis revealed a model accounting for 29.7% of variance (R = 0.545, R2 0.297, adjusted R2 0.269). Gender was not significant after height, age and body mass were entered into the regression analysis. This is the first study to report the contribution of non-disease related factors on distance achieved on the 12MWT in the GSDV population. The reference values generated will allow for improved monitoring and assessment of GSDV patients in clinical and research settings.