The Weight of Our Hands: Why We Underestimate and Its Implications for Prosthetics and Weight Disorders

Research has shown that people generally greatly underestimate the weight of their hands. In fact, most are almost 50 percent off.

We use our hands every day for anything and everything. But have you ever thought about how much they weigh? In a new study researchers put twenty volunteers in front of the block and got them to guess the weight of their hands. And the findings show that, in fact, we don’t know how heavy our limbs are at all.

Artificial limbs
Although we can accurately measure the weight of our hands, it turns out to be considerably difficult to estimate this correctly. An interesting phenomenon. “Weight is a fascinating concept,” says researcher Elisa Raffaella Ferre in conversation with Scientias.nl. “According to Newton’s laws, the weight of an object – and therefore of our hand – is determined by multiplying the mass by gravity. However, we do not have specific sensory receptors that allow us to directly measure the weight of our body parts. Moreover, the exact factors that influence our perceived weight are unknown.”

Experiment
In an attempt to find out more about this, the researchers conducted an experiment. Twenty participants were asked to sit in a chair and place their arm on the armrest, causing their hand to dangle down. A screen covered the arm so that participants could not see it during the experiment. Weights were then attached to the wrist. The participants now had to say whether these weights weighed more or less than their own hand. This exercise was repeated several times with different weights.

Underestimate
Spoiler alert: an average human hand weighs about 400 grams. But hardly any participant accurately estimated the weight of his or her hands. “On average, they consistently underestimate the weight of their hand by as much as 49.4 percent,” says Ferre. “Interestingly, this was the case for almost all volunteers.” So the experiment shows that most people misjudge the weight of their hands. And how! Your hands weigh as much as twice as much as you think they do. Why are we so far off? “The underestimation of hand weight may help us to better assess the weight of objects we hold,” Ferre suspects.

Second experiment
In a second experiment, the same participants again had to guess the weight of their hands, but this time they first had to squeeze a grip strength device for ten minutes, which made their hand feel tired. The team found that in this case, the subjects only underestimated the weight of their hands by 29 percent. Basically, the more tired their hands felt, the heavier they thought they were.

Measuring body parts
This means that when our hands are more tired, we are slightly less wrong.
And Ferre can explain that too. “The human brain has the ability to encourage or discourage physical exertion,” she explains. “For example, our brain can make our body feel light – resulting in effortless movements – or make it feel heavy – resulting in strenuous movements.” In other words, our perception of our body weight is often related to fatigue. For example, when you are very tired, your eyelids feel much heavier than when you are rested. This then leads to a certain action, namely going to sleep. “We hypothesize that perceived weight plays an important role in a system that evolved to regulate our behavior,” continues Ferre. “This idea is supported by our second experiment, which shows that the subjects estimated their hand weight to be higher when they had more tired hands due to the exercises performed. This clearly indicates that the brain plays an important role and controls our behavior.”

Better prosthetics
The findings from the study may be useful in the development of better prostheses. Previous research has already shown that many people with artificial limbs find them heavy. And that is actually quite remarkable. Such prostheses are often lighter than natural limbs. But if people could be convinced that their prostheses are “real,” they might no longer feel heavy. “Understanding how we perceive the weight of our limbs can therefore be useful in prosthetic design,” says Ferre. “The misperception of our perceived weight could be better taken into account.”

The study sheds light on how our brains perceive the weight of body parts. A first. Previous studies have focused exclusively on the social or medical aspects of how people feel about their total body weight. Surprisingly, no research has yet explored the more basic issue of how the brain estimates the weight of individual body parts. “And this is also crucial,” says Ferre. “For example, our research has important implications for our understanding of certain weight disorders, such as anorexia and obesity.”

2023-08-07 06:31:41
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