Jennifer Aniston has one of the most enviable bodies in Hollywood, with seriously sculpted arms and lean, toned legs.

A dedicated Pilates fan, it's no wonder the 54-year-old looks so fabulous – though over the weekend the Morning Show star revealed she has a helping hand in keeping her legs slim.

Jen took to Instagram to share a photo of herself makeup-free and lying on the floor, with her legs encased in a pair of oversized, inflatable pants that raised questions among her fans.

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"Re the pants, I have questions," one wrote, while another commented: "I want to know about the pants thing too!" A third wrote: "Can someone explain to me what is going on with the huge electric pants??"

The huge pants are in fact compression pants, also known as lymphatic drainage pants, which inflate and deflate to help ease water retention, leaving the legs looking more toned. 

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Jen's fans rushed to explain the high-tech device to one another, writing: "It's restore compression. Works wonders after running or walking etc. It feels amazing."

Another explained: "It's a pneumatic compression device - they can be used to prevent Deep Vein Thrombosis (clots in your legs), improve circulation, improve lymphatic drainage etc).

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Given Jen's highly active lifestyle, it's likely she loves compression pants to help her legs recover from activity and make them feel lighter.

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What are compression pants?

Compression pants are filled with air chambers that inflate and deflate, mimicking a lymphatic drainage massage.

According to Body Ballancer, who creates the pants, the massage action of the chambers inflating and deflating increases circulation to rid the body of waste and ease water retention.

A side effect of boosting your circulation and reducing water retention is that swelling is decreased, making legs look toned and slim, with the appearance of cellulite reduced too. It's this reason that many celebrities including Vanessa Hudgens jump into a pair ahead of big events.

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As for injury recovery, lymphatic drainage pants support the body's natural circulation to accelerate recovery, reducing muscle soreness and relieving fatigued muscles.

Jen might also wear the pants to relax, as the rhythmic motion of the inflation and deflation is ultra-relaxing when you get used to it.

Compression pants work quickly, which when you're as busy as Jennifer is surely a bonus, Heavy legs, tightness, water retention muscle soreness can be relieved with just one session in the pants.