You aren't just imagining things: You might weigh slightly more after strength training, particularly if you're just starting a workout plan. However, any spike in weight that shows up the next day is water weight. Exercise does not cause fat gain, and it typically takes longer than a day to gain enough muscle to register on the scale. Water weight usually disappears within days, so don't use the gain as an excuse to skip the gym.
About Strength Training
You don't need to lift weights for a serious strength-training workout. Body-weight moves such as pushups and squats also count, as do exercise-ball routines and even strenuous yoga sessions. Unlike cardiovascular exercise, which you sustain for at least 10 minutes a pop, strength training involves short bursts of activity -- enough to wear out your muscles after about 12 repetitions. Strength training is excellent for your health because it leads to stronger bones, better balance and possibly even sharper mental focus, according to MayoClinic.com.
If you've been lounging on the couch for the last year and then just yesterday picked up some dumbbells, your muscles are probably a bit shocked. They will let you know this by becoming sore over the next few days; this results from small tears in muscle tissue, inflammation and yes, fluid retention. This phenomenon is called delayed onset muscle soreness, and the extra fluid can add 3 or 4 pounds to your weight.
Preventing Water Weight
It's easy to get discouraged when your exercise plan makes you gain instead of lose weight, but transient water weight is largely preventable. Instead of jumping into an intense strength-training routine -- or a vigorous cardio routine, for that matter -- take it slowly at first. Start with just one set of each exercise, and don't take on more weight than you can easily lift. The best way to identify an overzealous workout is to pay attention to your muscles the next day; if they're very sore, you're probably experiencing water-weight gain.
Strength training can also lead to weight gain over time, but think of this as "good" weight. The activity builds lean muscle tissue, which is healthy but denser than fat tissue. Your measurements may shrink as you burn fat and add muscle, but the muscle tissue weighs more per square inch, so the number on the scale may climb even as your jeans get looser. Unlike water-weight gain, you will retain the added weight as long as you keep the muscle.
The best way to counter muscle-weight gain is by burning more fat. And while exercising is a great first step in shedding fat, what you eat matters more. Most women can lose weight on 1,500 calories per day, or up to 1,800 with regular exercise. Ensure proper nutrition by filling half of your plate at each meal with fresh or lightly cooked veggies and fruits, and divide the other half between grain products and low-fat proteins such as seafood, black beans and tofu. At least half of your grains should come from whole foods such as wild rice, barley and whole-wheat bread.
Nina K. is a Los Angeles-based journalist who has been published by USAToday.com, Fitday.com, Healthy Living Magazine, Organic Authority and numerous other print and web publications. She has a philosophy degree from the University of Colorado and a journalism certificate from UCLA.