Strengthening and toning your abs requires no more or no less effort than any other muscular group in the body. The American Council on Exercise recommends resting a day in between abdominal workouts to allow for muscular recovery and growth. Over-training or doing abdominal routines several days in a row may contribute to burnout or injury. Doing two to three abdominal strength training sessions each week will help build muscle and tone the stomach.
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Muscular Anatomy of the Abs
The rectus abdominus runs vertically down the front of the abs and laterally flexes the trunk. The external and internal obliques laterally flex the trunk and are on both sides of the abs. The transverse abdominus runs the width of the lower abdomen and is responsible for abdominal compression.
Form and execution are equally as important as frequency of abdominal training. Performing more than 25 repetitions of an abdominal exercise is too many and indicates that either your form is incorrect or that you are overcompensating with other muscles or momentum. Check your speed and form if this happens during your routine. Consult with a personal trainer if you are unsure of your form or for individual exercise guidance.
Abdominal Exercise Variation
Exercise variation is key to developing strong abdominal muscles. Training the same abdominal muscles each session may lead to a plateau and stall your muscular development and gains. Switching the abdominal exercises and focusing on different muscles will ensure you are not over-training a certain area during your bi-weekly workouts. For example, bent-knee sit-ups and pelvic tilts strengthen the rectus abdominus, while twisting bent-knee pushups and curlups strengthen the obliques. Performing an isometric exercise, such as the plank, strengthens the transverse abdominus.
Importance of Recovery
Abdominal strength training causes microscopic tears in your stomach muscles' fibers. ACE recommends waiting 48 hours in between strength-training routines to allow proper time for the tears to heal and rebuild as stronger muscle fibers. Exercising your abdominal muscles before the recovery period is over may injure your muscles and hinder your efforts.