Environmental conditions are important to consider when designing an exercise program. In this blog, we take a closer look at the implications of exercising in the cold, and how to design programs that are safe for your clients—even on winter’s coldest days. Exercising in the cold can lead to multiple conditions, including hypothermia, frostbite or a generalized vasoconstriction effect, which can be dangerous for individuals with hypertension and/or heart disease. Chilling can occur quickly when the body is wet from sweat, and heat loss is also accelerated in windy conditions, so there is much to consider when making exercise recommendations for your clients during the cold winter months. You should be familiar with the windchill factor chart and understand that, as temperatures decrease and wind speeds increase, the greater the danger for negative health consequences. Here are some important tips to share with your clients: Wear several layers of clothing, so that garments may be removed or replaced as needed. Remove outer layer as intensity increases and then replace these layers during rest or cool-down periods. Allow for adequate ventilation of sweat as wet clothing will continue to drain the body of heat. If there is any meaningful wind, it is better to begin your session going into the wind and to finish with the wind at your back. Select garment materials that allow the body to give off heat during exercise and retain body heat during rest. Wool is an excellent choice for exercising in the cold as it maintains body heat even when wet; cotton, however, is a poor choice as it absorbs sweat. New synthetic materials are also a good choice as they help to wick moisture away from the body. Nylon is a good choice for outerwear when windchill is a factor, but synthetic materials like Gore-Tex are probably the best choice because they block wind and are waterproof, which allows moisture to move away from the body. Replace body fluids in the cold. Monitor body weight over several days because sweat loss may not be as evident in the cold. For more information about exercising in the cold, please refer to Chapter 2 of ACE’s Essentials of Exercise Science for Fitness Professionals.