Use the Nike Resistance Loop - Black/White to help strengthen your legs

The Nike Resistance Loop is made with a durable construction for lasting use, the knit material is soft and comfortable with thin silicon interior grips to help keep the band in place when exercising.

Size guide; select band size based on your body weight.
S = Less than 120lbs/54kg
M = 125-170lbs/57-77kg
L = 175-205lbs/79-93kg