A recent study conducted by scientists at Birkbeck University of London found that people in general underestimate the weight of their hands by more than 49%. The study, which asked participants to compare the weight of their hands to various objects, found that their hand weight was about 400 g (14.1 ounces). This underestimation of one’s own mass was called “earth weightlessness” by the researchers. The results of this study have important implications for prosthetic users, as many people perceive their prosthetics as too heavy, even though they are much lighter than real limbs.
Body weight perception is not directly related to specific sensory cues, making it difficult to determine how our brains determine weight. Previous research on body weight has focused on the social and medical aspects of people’s attitudes toward overall body weight, but has done little research on how the brain forms perceptions of the weight of individual body parts.
The study involved 20 healthy adults who were asked to relax their left arm on an armrest-like support. The arm was covered with a screen so that participants could not see it. Researchers supported the participants’ arms and added weight to the left wrist, starting with 100 grams and gradually increasing to 600 grams. Participants were asked to rate how much lighter or heavier their hands or the weight was at each stage.
“Our results show that our everyday perception of body weight – weightedness – can be accurately quantified and is highly underestimated.” – Elisa Raffaella Ferre, neuroscientist
On average, participants underestimated the weight of their arms by 49.4%. Interestingly, if participants experienced fatigue by squeezing a grip strength device for 10 minutes before starting the experiment, they underestimated the weight of their hands by only 29%. This suggests that fatigue affects weight perception, and more fatigued people perceive their hands as lighter.
The results of this study provide a new method for studying how the brain perceives body weight. Understanding how our brain determines weight may have implications for the design and use of prosthetic limbs, as well as the general understanding of human perception. The researchers believe that perceived body weight may be an important component of the system that encourages or discourages physical activity. This phenomenon may play a role in controlling the level of our behavior.
Neuroscientist Elisa Raffaella Ferré, one of the lead researchers, explains, “Our results show that our everyday sense of body weight – weightiness – can be accurately quantified and is highly underestimated.” Denise Cadete, PhD student and researcher, adds: “Surprisingly, no study has explored the more fundamental question of how the brain constructs representations of the weight of individual body parts.”
“Surprisingly, no study has examined the more fundamental question of how the brain constructs representations of the weight of individual body parts.” – Denise Cadete, PhD student and researcher