Have you been exercising and eating right, but the scale says you are gaining weight? Here are four things you need to know about your weight fluctuation with exercise: 1. Water Retention After Exercise The amount of water in your system has a heavy influence on the number you see on the scale. Exercise can increase or decrease water weight. 2. Weight Gain Immediately After a Workout Changes in hydration, inflammation, and urine and blood volume after a workout can affect your weight. 3. Weight Gain with Strength Training Exercising can change body composition by building dense muscle and decreasing body fat. 4. Weight Gain from Muscle vs. Fat Weighing yourself can be one way to track your progress, but it shouldn't be the only way. It's definitely not worth obsessing over with daily weigh-ins.