4-week training cycles are by far the most popular. These cycles are sequenced and produce results in four weeks. Sequenced training produces the most results throughout your training cycles. Not only do you get results from a cycle you are currently in, those results are what help maximize the cycle that follows. For example, a hypertrophy training cycle is designed to maintain and build lean muscle mass, get more tone, lean-up, decrease body fat, and improve percent body fat. You can realize some of these benefits if you do a hypertrophy cycle; you’ll maximize these benefits if you run an anatomical adaptation cycle immediately before starting your hypertrophy. Science has proved this! Every workout you do in the 4-week cycles is defined and detailed for you.
12-week training programs are as complete as it gets. They combine three 4-week cycles that include an anatomical adaptation, hypertrophy, and strength cycle. These programs are more specific and culminate with a challenge. If you want to tone up your core, the last 4-week cycle is a program very specific to developing your core (core training is the main focus progressed over 4 weeks).