Few things make laundry more difficult to deal with than clothing that is full of sweat and odour. Workout and work clothes are the most common culprits; even after washing and drying, the odour seems to remain, which can be frustrating for whoever gets stuck doing laundry, or for you if they're your clothes. Rather than throw them out and buy new ones, adjust the laundry process to see if the clothing can't be salvaged.
While many of the daily laundry detergents available have been adjusted for high-efficiency washing machines and claim to fight stains and odour, not all do so effectively. Opt for a detergent that specifies it contains oxygenated ingredients, which are designed to fight stains and clean clothes "cleaner" than competing detergents. Wash with warm water, despite the "cold water is OK" claims, which may solve the sweat and odour problem in some clothing.
Washing Powder Booster
Washing powder boosters are powders that you add to the washer when loading it with dirty clothes. Used in conjunction with your regular washing powder, the booster helps combat the effects of low-quality water sources and average (non-high-tech) washing machines. Typically, the washing powder booster is sold in boxes in the washing powder aisle of the grocery store (brands such as Borax or Arm & Hammer). Add about a cup of the booster to the load of laundry, and don't forget to add the washing powder too. Use warm water for these as well. If the booster powders are unavailable, add about a 1/2 cup of baking soda to the laundry instead.
Line Dry Your Clothes
Sometimes line-drying clothes in the sun effectively removes the sweat and odour that has been trapped in the fabrics. Wash as you normally would, or with one of these suggested methods, and remove the clothing from the washer immediately; don't let the laundry sit in the washer once it's finished. Take the laundry outside, and hang it on a clothesline where it has access to direct sunlight. Once the clothes are dry, shake them out and fold immediately.
Change Your Laundry Habits
Washing powder bottles give instructions for how much detergent to use in each load, usually based on size of the load of laundry and type of machine. Many also specify they work equally well in cold water. For sweat and odour in clothing, standard instructions cannot apply because the instructions are designed for standard laundry in general. Change to warm water options on the washing machine, and add twice the suggested amount of detergent and dry clothing with two or three scented dryer sheets. Also avoid leaving laundry in the hamper (or in a pile) when dirty, in the washer after the washer has stopped or in the dryer after the dryer has stopped; leaving laundry to just "sit" can cause odours to remain or allow the odours in some clothes to rub off on others.
Soak Laundry Before Washing
Wash sweat-filled and odorous laundry in separate loads even if there are only a few items. Do not allow them to sit with other laundry, and wash them promptly after use. If using a traditional top-load washer, turn the washer on and add the detergent and booster (if using) with the sweaty, smelly laundry. When the washer is full (before it starts agitating), open the lid and allow the laundry to soak for 20 to 30 minutes; then close the lid, and allow the wash to finish, which may help extra-stubborn sweat and odour.