Occasionally everyone feels a random bout of weakness during a diet and exercise regime, because it’s the body’s way of rebooting or adjusting to the workload. But according to the National Federation of Professional Trainers, feeling chronically weak or fatigued during dieting and exercise for a sustained time may signal an infection, illness or other serious health-related condition. If you feel weaker than usual during a diet or exercise program or notice any changes in your energy level lasting more than a few days, contact your physician.
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One common cause of feeling weak during an exercise program is overtraining. When you start a new fitness program, you may not know how many times a week you should train or how long your sessions should be. According to the American Council on Exercise, overtraining can lead to dehydration -- which can cause you to feel dizzy, fatigued and nauseated. Overtraining can also cause chronic muscle fatigue, which makes it impossible for your muscles to keep up with the amount of tears you cause through exercise. Try taking a week off from training to see if you begin to feel better. If this weakness persists, contact your physician.
Not Enough Carbs
Not eating enough food -- mainly carbohydrates -- is often a cause of feeling weak during a diet or exercise program. Low-carb diets have enticed many people to experiment with unhealthy means of dieting, often leading to a variety of health-related conditions. Carbohydrates are your body's main source of energy. They contain many life-sustaining vitamins and minerals. Limiting carbohydrates to dangerously low levels can cause hypoglycemia, malnourishment, muscle atrophy and fatigue.
If you begin a diet and exercise regimen and notice you begin to feel weaker or fatigued, it may be due to an untreated illness. According to the American College of Sports Medicine, some medical issues known to cause weakness and fatigue are anemia, fibromyalgia and obesity. It’s possible that the stress from exercise can cause an illness to manifest itself through weaker muscles. This is especially true with fibromyalgia and obesity. If you suspect that your weakness may be due to an untreated illness, seek medical attention.
Changes in diet and physical activity can cause a drop in your immune system, leaving you susceptible to bacterial, fungal or viral infection. Typically in an exercise environment, a large amount of germs take advantage of your low immune system and use the opportunity to invade your system. If you exercise in an environment that is unclean or used by others, you may have caught a bug that caused you to become weaker due to infection. Improper dieting can also cause your immune system to weaken if you don’t get enough essential vitamins and minerals. It’s best to see your doctor if you feel you may have recently been exposed to any pathogens.
Do not equate "diet" with starvation. A well-balanced diet that includes complex carbohydrates and protein is essential. Not eating enough or not eating the right kinds of food will leave you feeling weak and dizzy during or after a workout. Approach "dieting" as a lifestyle change and develop a healthy eating plan. The Centers for Disease Control and Prevention has guidelines for developing an eating plan that will help you manage your weight.