Once a low-risk pregnancy has been established, walking in combination with nutritional control may be effective in preventing excessive weight gain in overweight and obese women. Maternal exercise prescription should use the Frequency, Intensity, Time spent and Type of exercise principle, with a frequency of three to four sessions per week as ideal. Intensity based on a target heart-rate zone of 110 to 131 beats per minute for women 20 to 29 years of age and 108 to 127 beats per minute for women 30 to 39 years of age, coupled with use of the rating of perceived exertion scale and the "Talk Test" is suggested. Dieting and exercise together are most effective in reducing weight retention after childbirth and compliance may be improved by incorporating child-care and children into the exercise routine. After medical consultation, postpartum women should begin exercise slowly, starting from 15 minutes, and building to at least 150 minutes of aerobic activity per week, with this activity spread throughout the week.