Men's Fitness explains that a good way to keep clothes smelling fresh is to pre-treat them by hand before throwing them in the washing machine. For machine-washable clothes and bedding, dilute 2 ounces of detergent in one-half gallon of warm water and scrub the neckline, armpits and other high perspiration areas.
For heavily soiled items like gym clothes, it is important to check the washing machine capacity and only fill it to three-quarters of the total. Filling the washer up too much will prevent the entire surface area of the clothing from being exposed to water. If the odor of sweat is strong, squeeze an entire lemon in to the detergent-and-water solution before pre-treating. The citric acid in the lemon juice helps to break up the oils and organic compounds from the skin. White vinegar can be used in place of the lemon juice to produce a similar acidic solution. Also, it is important to not use too much soap, as increasing the amount of soap only works to increase water viscosity, which will prevent the water from penetrating the fabric of the clothes. To eliminate the odor of the vinegar or lemon juice, tumble dry clothes on low with scented dryer sheets.