Carbohydrate is the predominant energy source during a strength training workout. Stored as glycogen in the muscles, it is the fuel used to supply energy for short, intense bursts of power. The harder and longer you work out, the more glycogen your muscles require. Once these stores of glycogen are gone your energy level will drop and you will run out of fuel to power muscle contractions. For this reason, athletes doing strength training exercise in the hopes of building lean muscle need to have an adequate carbohydrates intake.
Your carbohydrate needs will vary depending upon the intensity and length of your training sessions. For those doing moderate workouts of less than an hour, you may only require 2 grams of carbohydrate per pound of body per day. Those doing long, intense training two hours or more, may require 3-4 grams of carbohydrate per pound of body weight each day.
Sports nutrition experts recommend up to 400-600 grams of carbohydrate per day for the average male performing regular intense exercise and strength training workouts in order to keep the muscle glycogen stores high. Personal carbohydrate requirements vary based upon the intensity and length of workouts as well as you body size.