Rating of perceived effort (RPE) scales are the most frequently used single-item scales in exercise science. They offer an easy and useful way to monitor and prescribe exercise intensity. However, RPE scales suffer from methodological limitations stemming from multiple perceived effort definitions and measurement strategies. In the present review, we attend these issues by covering (1) two popular perceived effort definitions, (2) the terms included within these definitions and the reasons they can impede validity, (3) the problems associated with using different effort scales and instructions, and (4) measuring perceived effort from specific body parts and the body as a whole. We pose that the large number of interactions between definitions, scales, instructions and applications strategies, threatens measurement validity of RPE. We suggest two strategies to overcome these limitations: (1) to reinforce consistency by narrowing the number of definitions of perceived effort, the number of terms included within them, and the number of scales and instructions used. (2) Rather than measuring solely RPE as commonly done, exercise sciences will benefit from incorporating other single-item scales that measure affect, fatigue and discomfort, among others. By following these two recommendations, we expect the field will increase measurement validity and become more comprehensive.