It is especially from the 1980s that the scientific studies on exercise with reduced breathing frequency began to be published. While the method advocated by Counsilman attracted a following in some runners and athletics coaches, the results of the studies contradicted the hypotheses put forward by the World of Sport. They showed that this training method did not decrease body O2 concentrations and provoked only a hypercapnic effect, i.e. an increase in CO2 concentrations. Both the effectiveness and legitimacy of hypoventilation training were strongly challenged.