The primitive men, who became extinct about 30,000 years ago after human ancestors arrived in Europe from Africa, were presumed to have spent most of their time hunting prey.
But a new study suggests that their daily lives were in fact much more mundane, with tedious tasks like processing animal skins to make clothing accounting for several hours of each day.
Researchers from Cambridge University came to their conclusion after studying possible causes for the overdevelopment of the right arm bones which is common among Neanderthal skeletons.
While humans typically have a right arm which is between five and 15 per cent stronger than their left, some Neanderthals had upper arm bones which were 50 per cent stronger on the right side.
Previously, it had been assumed this was caused by right-handed Neanderthals spending an excessive amount of time hunting large animals with spears, which built up their arm strength.
The new paper, published in the PLOS One journal suggests the imbalance more likely developed as a result of spending hours scraping animal hides with stones – a stage in the production of clothes.
Such a task would have required them to make a forceful and repetitive scraping motion for several hours at a time, making it a much more likely cause of the distinctive trait, researchers said.
Dr Colin Shaw, who led the study, said: "The asymmetry we see in the arms of Neanderthals is far more profound than anything we encounter in modern humans except some sportspeople, such as cricketers and tennis players.
“The skeletal remains suggest that Neanderthals were doing something intense or repetitive, or both, that had a significant role in their lives. If it was hunting, it was taking up a great deal of their time. Not surprisingly, that theory has coloured our view of Neanderthal ‘the hunter’.
“Our research moves away from that perspective. Hunting was an important part of the lives of Neanderthals. However, for much of their time Neanderthals might have been performing other tasks, such as preparing skins. If we are right, it changes our picture of the daily activities of Neanderthals.”
The researchers tested their theory by asking groups of right-handed men to perform actions replicating the repeated scraping of a hide and a two-handed spear thrust to kill large prey.
By measuring the electrical potential produced by shoulder and chest muscles during each activity, the scientists could calculate the approximate load being placed on the upper arm.
They found that using a spear against a target produced more muscle activity in the left arm than the right, because the left hand was closer to the point of impact.
In contrast, the scraping task caused muscle activity on the right side in exactly the areas which would over time cause the right arm to become overdeveloped, the researchers reported.
Studies of the preparation of animal hides by traditional populations in Ethiopia, Alaska and Canada today show that it can take eight hours to scrape a single hide.
Scraping hides would likely have been an activity that Neanderthals had to carry out because they would have needed warm clothing to survive, researchers added.
A stone tool known as a racloir, or "side-scraper", used to remove soft tissue from animal hides, is often found alongside Neanderthal remains.