Do you really need electrolyte supplements?
For most people who eat a normal diet, electrolyte supplements are not necessary. They are only useful during prolonged exercise lasting more than 90 minutes or during the first days of exercising in the heat.
People who eat a normal diet already get enough electrolytes from food to replace what is lost through sweat and urine. Supplements add nothing in that case. Only during the first few days of exercising in the heat can extra salt be useful, because the body still needs to adjust to the higher sweat losses.
For exercise lasting less than 90 minutes, plain water is sufficient. Electrolyte drinks offer no demonstrable benefit within that window. When exercise lasts longer than 90 minutes, sports drinks containing carbohydrates and electrolytes can support performance, but the effect of the carbohydrates plays at least as large a role as the electrolytes themselves.
A fluid deficit of more than 2% of body weight measurably impairs performance: heart rate rises, the body stores more heat, and effort feels harder. This effect is stronger in warm weather. People who are accustomed to heat also sweat more and therefore need to pay extra attention to drinking enough, because dehydration cancels out the benefits of that acclimatisation.
But drinking more than you need is not a solution either. Excessive fluid intake can lower the sodium level in the blood to a dangerously low level, a condition called hyponatraemia. It is preferable to match your fluid intake to your actual sweat losses rather than drinking as much as possible. Finally, using large amounts of sodium-containing electrolyte supplements over a long period without a medical reason can raise your blood pressure. Guidelines set an upper limit of less than 100 mmol of sodium per day.
This answer is based on several review studies and targeted experiments in athletes. The effect of dehydration on performance is well supported and has been confirmed repeatedly. The comparison between types of sports drinks (hypotonic versus isotonic) rests on a review of multiple studies, but the difference is small and the clinical significance is uncertain; one of the authors of that review previously had financial ties to sports drink manufacturers. The evidence on hyponatraemia and the blood pressure risk associated with high sodium intake is reasonable, but exact threshold values are absent from the available summaries.
How much cardio do I really need per week?
For a healthy adult, 150 minutes of moderate cardio per week is the well-supported minimum, supplemented by two strength-training sessions; if you want to maintain your weight, you are better off aiming for 225-420 minutes per week.
How much protein do I need to maintain my muscle mass?
For most healthy adults who want to maintain their muscle mass, 1.2 to 1.6 grams of protein per kilogram of body weight per day is a well-supported target, especially when combined with strength training.
Is walking enough, or do I really need to do strength training too?
Walking is good, but strength training adds something walking cannot: preserving muscle mass, strengthening bones and keeping your metabolism in shape. Even half an hour of muscle-strengthening exercises per week makes a measurable difference.
Does stretching actually help, or is it a waste of effort?
Stretching demonstrably improves flexibility, and 10 minutes per week is already enough for the maximum effect. For preventing injuries, however, it does not work; eccentric strength training is far more effective for that purpose.
How much exercise do I need to live longer?
The biggest health gain comes from just a little exercise. Going from nothing to 150 minutes per week gives a 31% lower risk of premature death; after that the benefit increases somewhat more, but levels off.
Does walking do enough to maintain your muscles?
Walking alone is not enough to maintain muscle as you age. Add strength training and ensure adequate protein intake for the best results.