The purpose of this study was to investigate the consciousness among young people (n = 1016) on training body part(s), using a questionnaire-based survey showing participants a picture of a single-joint exercise. The participants were shown a picture of knee-extension exercise (KNEE-EXT), and were asked to identify the body part(s) they felt were being trained. On seeing the picture, more than 90% of the participants felt that KNEE-EXT can train the anterior thigh part. However, more than 90% of the participants who had no experience doing KNEE-EXT felt that the exercise trained not only the anterior thigh part but also other parts, including the trunk, the posterior thigh, and the upper limb. Among those participants who had performed KNEE-EXT without the experience of strength-training under professional supervision, approximately 80% felt that the exercise was appropriate to train not only the anterior thigh but also other parts. These results suggest that performing exercises by referring to only a picture may result in the individuals not properly understanding how the body part(s) should be trained during exercise, even in single-joint exercises. Appropriate supervision is of even greater importance especially for strength-training beginners. Furthermore, even among participants who had an experience of exercise under professional supervision, approximately 60% had a similar response. Therefore, to enhance the benefits of exercises, individuals (even those who have had experience in training under professional supervision) should always be instructed under appropriate supervision on the correct technique and knowledge about the exercises.