Many people go into the HCG diet wondering whether or not they should continue to maintain or elevate their level of exercise to assist in weight loss throughout the diet's duration. This common question is definitely important and you shouldn't go into the HCG diet if you're unsure about what your body can and cannot take, as potentially harming your diet (and your body) is a real possibility if you don't allow yourself the proper nutrition while exercising.
The first thing to understand going into the HCG diet is that you will be restricting your caloric intake, which disallows any real vigorous exercise, because on such a low calorie diet your body will struggle to keep up any rapid pace, high intensity workouts for an extended period, likely leading only to frustration as you're unable to keep up the usual tempo, as well as the water your body would retain afterwords leading to discourage results on the scale.
Losing weight will also come so quickly on the HCG diet that even people who maintain a strict regimen of exercise will likely not think they have to continue while on the diet.
But if you're one of those people who either work a physically demanding job or just have to be on the move, then adding calories while on the diet is also acceptable. You'll likely see slower results when it comes to the scale, but fat loss should remain constant.
Things to consider adding to your diet will be things like egg whites, a protein shake, or just a larger serving of protein than usual. It's hard to be exact on how many calories to add individually, which is why I recommend using something to calculate how many calories you burn during the exercise (such as myfitnesspal's calorie counter), but a general rule to follow is to add at least 100 to 250 calories on the days that you exercise.
Strength loss should be expected on the diet, as losing such a large amount of weight will no doubt result in some muscle loss, simply due to the fact that when you lose weight, especially a signifigant amount, you lose it everywhere. But the loss of fat will allow for post-diet workouts to be more intense and last for a longer time as it will be that much less weight for your body to have to keep energized for the duration.
Outside of an intense workout or a long day working a job such a construction, very light exercise is recommended for almost everyone on the diet. Things such as yoga, easy biking, a light swim, or even a medium distance walk can all help during your diet. Light exercise will assist in maintaining muscle tone, keeping your cardiovascular health on pace, and just provide the stress relief associated with these activities.
Once the diet is completed, your normal routine can be assumed with no issue. Everybody's body is different, though, and before attempting to exercise while using HCG be sure to visit a trusted physician to make sure you're okay to exercise while on the diet.