There are several possible reasons for muscle cramping during exercise.
• Over-doing it or undertraining is the most common. When first beginning to exercise – and this includes walking and other physical activity – you should begin slowly and gradually increase your activity as your level of fitness increases. If the muscle cramping is due to this cause, it should improve over time (not get worse), and only cause pain while walking.
• Another possibility is low potassium, sodium and/or other minerals. While following a lower carbohydrate diet, it’s generally recommended that you take a good multivitamin with minerals supplement along with an additional potassium supplement and extra salt.
• A third, but unlikely cause, is loss of body fat. When people lose too much body fat, it’s often first noted in the feet. If this were the case, you would probably feel colder than usual. This cause is not usually seen until people reach a VERY low body fat (less than 10% in men or 15% in women).