In a previous review in 2004, sports scientists were recommended to use single-subject research designs to understand how well an intervention works and to predict performance for an elite athlete. In the present paper, the latest studies on elite athletes’ conditioning using single-subject research designs are reviewed. Although some case studies in elite athletes are reported in the literature, ... [Show full abstract] there are still very few studies using single-subject research designs. Rigorous and practical approaches using magnitude-based inferences such as effect size and likelihoods of substantial effects are suggested. Recommendations are also provided to facilitate further studies using single-subject research designs.