The average energy consumption for 30 minutes of walking in regular sneakers is around 75 – 150 calories, depending on pace, but with the new Muscle Trainer sneakers you can apparently increase energy consumption to 300 calories in the same interval.

So what makes Muscle Trainer sneakers so special? Well, it’s the increased weight. The average sneaker weighs between 200 and 400 grams, but Muscle Trainer sneakers will add between 1,200 grams (for women) and 1,400 grams (for men) of extra weight to each foot. All the extra weight is concentrated in the internationally-patented sole, which contains hundreds of small iron balls. However, thanks to their high-cut design that protects the ankles, and high-quality materials, the sneakers are very comfortable while at the same time working your leg muscles.

The recently launched Muscle Trainer sneakers were apparently tested by scientists at Tokyo Gakugei University and Osaka Wako University, at the request of the manufacturer. They concluded that the “fat burning” and “muscle training” effects can be obtained more efficiently with the Muscle Trainer sneakers compared to other footwear, and that the calorie burning process is increased by 25%. Researchers noted that the Muscle Trainer sneakers can help prevent lifestyle diseases like diabetes and hypertension.

Muscle Trainer sneakers are currently available in black and white, at a price of 13,600 yen ($122).

So if you’ve ever considered tying some extra weights to your feet to get a better workout, putting on these sneakers accomplishes the same thing, basically.