CommentaryOur previous paper prompted a lively debate concerning the efficacy of sprint interval training (SIT) [1,2]. For clarification, SIT refers to protocols that involve supramaximal efforts (>100% maximal oxygen uptake) and high-intensity-intervaltraining (HIIT) involves 'vigorous' or 'near-maximal' efforts (target intensity: 80% to 100% peak heart-rate) [3]. In the current commentary, we return to the role of affect and perceived effort on exercise adherence raised in the recent commentary by Jung et al. [4]. We contend that the considerable anticipated effort required to participate in SIT and aversive psychological states experienced during such 'all out' supramaximal exercise may likely to damage adherence to such protocols.Although we recognize the health-related physiological benefits of classic SIT, which involves up to six 30-s-sprints, we agree that 'considering the need for specialized equipment and the extremely elevated level of subject motivation, this form of training may not be safe, tolerable or practical for many individuals ' [5]. Therefore, we contend that the considerable effort required to participate in classic SIT is such that it is unlikely to be experienced as pleasant and enjoyable for most people, especially those less active individuals [6].More recently researchers have proposed SIT protocols with fewer and shorter sprints than classic SIT [7][8][9]. For example, Metcalfe et al. [7] have proposed the reduced-exertion highintensity training, which involves two 'all out' 20-s-sprints, while Gillen et al. [8] have proposed a SIT protocol involving three 'all out' sprints of 20s. Despite the interesting preliminary findings regarding the health-related physiological benefits, adherence to these very-low-volume SIT protocols remains unknown. Moreover, it should be noted that these SIT protocols [7,8] were supervised in a laboratory setting. In a 'real world' setting, albeit supervised, Lunt et al. [10] reported drop-out rates were much higher in the SIT and HIIT groups compared to the walking condition (44% vs 18% respectively). Three (19%) SIT participants picked up an injury. These dropout rates are likely to be much higher in free-living HIIT and SIT programs. It is likely that high degree of effort involved explained some of the drop-out of participants from the study, which included inactive and overweight participants.We need not to refer solely to the Dual Mode model (DMM) to describe the negative affective responses to high-intensity exercise. Research has demonstrated a repeatedly negative association between perceived effort and exercise adherence [11]. We recognize that most of this evidence relates to continuous exercise protocols. However, Oliveira et al. [12] found that perceived effort predicted affective response during HIIT and Frazão et al. [13] showed a negative correlation between perceived effort and affective response during HIIT. Wood [14] also found similar declines in affect in SIT and HIIT. In our opinion the negative association between perceived effort a...