The answer is: nothing! The Swedish word hamstring can refer to the muscle, but it also means 'hoarding' or 'stockpiling'.
It is linked to the verb hamstra ('to hoard') which comes from the noun hamster, meaning 'hamster', the rodent often kept as a household pet.
Think of how hamsters store food in their cheeks to ensure they have enough nutrients for later. That's why this word is used to describe people stocking up on food ahead of an emergency.
So hamstring often occurs during times of uncertainty, such as during the current coronavirus outbreak which has left some people fearful both of being stuck at home for a 14-day quarantine or of shortages due to possible delays from suppliers.
It's worth noting that while Swedish authorities generally recommend having enough non-perishable food at home to see you through a crisis, at the time of writing they had not recommended taking any specific actions to prepare for a coronavirus outbreak, beyond practising good hygiene and staying at home if you experience the symptoms of the virus.
And if you do have to stay at home during a quarantine, it's OK to receive deliveries from supermarkets, takeout apps, or friends — just make sure they drop your shopping off outside your door if you could be contagious.
You can use hamstra as an intransitive verb, with no object, for example: Folk har börjat hamstra (people have started stockpiling). And you can use it with an object, for example att hamstra mat/mediciner/varor (to hoard food/medicines/goods).
Oroliga kunder har börjat hamstra torrvaror
Worried consumers have started to stockpile dried foods
Allmänheten uppmanas att inte hamstra munskydd eller mediciner
The public is advised not to hoard face masks or medicines