Abstract Background Welders demonstrate a high prevalence of musculoskeletal disorders (MSDs), as indicated by high rates of illness-related absenteeism. Leisure time physical activity (LTPA) could be a preventive strategy. However, little is known about LTPA prevalence and its association with MSDs among welders. Aims The aim of this study was to analyse the prevalence of MSD and LTPA levels among welders and to identify risk factors for the main disorder of low back pain (LBP). Methods The following data were collected from 145 welders from 34 companies in the German steel industry: individual factors (demographics, health behaviour), job-related factors (welding process, welding hours per day, employment years, shift work, ergonomic tools) and MSD (Nordic questionnaire). LTPA (International Physical Activity Questionnaire) was calculated to determine the metabolic equivalent of task (MET) per week as an objective measure of energy expenditure. Prevalence and multivariate regression analysis were calculated to determine odds ratios (ORs). Results The 12-month prevalence of LBP was 71%, for neck pain 61% and for shoulder pain 55%. Forty-two per cent of the participants accumulated <600 MET/week. The multivariate regression model revealed LTPA <600 MET/week (OR 3.4, 95% CI 1.05–10.85) and neck pain in the previous 12 months (OR 5.2, 95% CI 2.02–13.56) to be significantly associated with LBP. Conclusions The results show a high prevalence of MSDs and thus a strong requirement for intervention. Therefore, LTPA should be prioritized and employers should encourage access to regular activity.