When choosing sportswear for walking or running on a treadmill, apply the same principles that you would to running or walking outside on a room-temperature day (68 degrees Fahrenheit). If you will be running on the treadmill, shorts and a short-sleeved top, tank top, or full-length bra top should keep you comfortable and prevent overheating. If you specifically want to sweat, wear long-sleeves and an extra layer. Speaking of layers: Whether you're walking or running on a treadmill, bring a light jacket or top with you in case you find yourself positioned uncomfortably close to a fan or air-conditioning vent and you start to feel chilled. Tie the jacket or top around your waist or around the treadmill railing for easy access.