Fitness & Exercise Community

It can take 3-4 weeks after donating blood to replenish all red blood cells and hemoglobin. But I am not an expert on blood levels or anemia and cannot answer your questions specifically. You can check the men's/womens health communities here at WebMD http://men.webmd.com/default.htm
http://blogs.webmd.com/womens-health/
As for lethargy related to exercise, it could be dehydration, or loss of electrolytes, or both. Your urine should always be clear, and you should be urinating 1.5 to 2 liters a day. A liter of water weighs app 2.25 pounds. Weigh yourself nude before and after spin to get an idea of how much fluid you lose, and replace at least that much, and more to accommodate for sweating after the workout. You didn't say what other exercise you do, and so if you're doing spin twice a week, and perhaps other intense workouts during the week, then maybe you're overtrained. Or if those 2 spin classes are all you do, then maybe you're not fit enough to push so hard 2x a week and nothing else. Of course, the number of calories you consume and nutrition in general could be factors as well. Iron is one of the minerals in sweat, although it's just a trace amount. I can't tell you how much iron you're losing in the sweat. And finally, there are many reasons for lethargy, and not all associated with exercise, and so if it continues then you ought to go back to your doctor about it.

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Here are exercise and hydration guidelines from the American College of Sports Medicine and the National Athletic Trainers' Association are the following:

1. Pre-Hydration: Drink 17 to 20 fl oz of water or a sports drink
2 to 3 hours before exercise to enable fluid absorption and allow urine output to return toward normal levels. 7 to 10 ounces of water or a sports drink 10 to 20 minutes before exercise.

2. During exercise fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces every 10 to 20 minutes during exercise. More than 2% loss of body weight will affect performance, particularly endurance performance.

3. CHO concentrations greater than 8% increase the rate of CHO delivery to the body but compromise the rate of fluid emptying from the stomach and absorbed from the intestine. Fruit juices, CHO gels, sodas, and some sports drinks have CHO concentrations greater than 8% and are not recommended during an exercise session as the sole beverage. Excessive CHO can cause gas, upset stomach, and diarrhea. Carbohydrate consumption at a rate of app 30-60 grams per hour has been shown to maintain blood glucose levels and sustain exercise performance

4. Post-exercise hydration should aim to correct any fluid loss accumulated during exercise. Rehydration should contain water to restore hydration status, carbohydrates to replenish glycogen stores, and electrolytes to speed rehydration. A liter of water weighs app 2.25 pounds. You should weigh yourself nude before and after exercise to determine how much fluid you lose so you know how much to replace.


5. Include CHOs in the rehydration beverage during exercise if the session lasts longer than 45 to 50 minutes or is intense. Drinking 1 liter of a 6% CHO drink per hour of exercise will be adequate.

6. Inclusion of sodium in fluid-replacement beverages or salted snacks should be considered to help stimulate thirst and retain fluids under the following conditions:
a. inadequate access to meals or meals not eaten;
b. physical activity exceeding 4 hours in duration;
c. during the initial days of hot weather.
Under these conditions, adding modest amounts of salt (0.3 to 0.7 g/L) can offset salt loss in sweat and minimize medical events associated with electrolyte imbalances (eg, muscle cramps, hyponatremia). Adding a modest amount of salt
(0.3 to 0.7 g/L) to all hydration beverages would be acceptable to stimulate thirst, increase voluntary fluid intake, and decrease the risk of hyponatremia (low sodium levels) and should cause no harm.

Take care, Rich