Water is vital for many chemical reactions that occur inside our cells, including the production of energy for muscle contraction. When you sweat during exercise, you lose body water that can affect cellular processes. In addition, your blood volume decreases and becomes thicker if you don't replace fluids, resulting in a lower stroke volume (amount of blood pumped by the heart per beat), cardiac output (amount of blood pumped by the heart per minute), and a decreased oxygen delivery.
Running performance starts to decline with only a two to three percent loss of bodyweight due to fluid loss. The best rehydration fluids are those that contain sodium, which stimulates your kidneys to retain water. If your run is of a low intensity and lasts less than an hour, plain water in combination with a balanced diet is just as effective.
A good indicator of your hydration level is the color of your urine, with a light color indicating adequate hydration. If your urine looks like apple juice, keep drinking.
With hard training comes muscle damage and inflammation, which is exacerbated with downhill running. This leads to muscle soreness and reduced muscle-force production. While research has shown that ice massage or immersion in cold water doesn't decrease the perception of soreness, it can decrease the level of the enzyme creatine kinase in the blood (an indirect indicator of muscle damage). So take a cold bath after your hard workouts and wear a hat to prevent hypothermia. Limit your stay in the water to about 10 minutes to prevent frostbite.
Limit Other Activity
Since any physical activity you do during the rest of the day when you are not running will influence your rate of recovery, it is important to limit your non-running activity. For example, if you are training for a marathon and run 20 miles on a Sunday morning, it would be unwise to go hiking with your kids and dog on hilly trails that afternoon, as that will affect your next run.
Taper Before Competition and Increases in Training Load
The most effective adaptations occur when you are recovered from previous training and best prepared to tolerate a subsequent overload. You can't train hard all of the time. While you improve your fitness during periods of hard training, you also increase your fatigue. Periodic decreases in training load will give your body time to adapt to the training stress and reduce fatigue, making you ready for a higher load of training.
How much or how long you need to taper depends on the severity of the training load, your level of fatigue and the distance of your upcoming race. Usually a week is sufficient, with a longer taper for longer races.
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