The best length for a training cycle is one that makes use of the adaptive ability of the body but does not lead to performance degradation and mental burn out.
The exact length of the cycle varies based on the situational factors of the person and the goal. Situational factors include but are not limited to a person's physical ability, training experience, time to reach their goal, schedule, and level of motivation. Each of these factors affects the training cycle and overall training program. For example, someone may have the availability in his or her schedule to workout five times per week but lack the motivation to do so.
The goal determines the training cycle based on the loftiness of said goal. Simply put, the harder the goal, the longer the total training cycle. For example, adding 300 pounds to a powerlifting total may take 12 months, but adding 50 pounds could take three months.
When considering a macro training cycle, which is the larger overall training cycle, you or your trainer must look at the goal in front of you and consider your situational factors. For example, if you want to add 300 pounds to your powerlifting total, you have a solid strength and skill base, and you can dedicate five days per week to working solely on powerlifting, then you may be able to add that 300 pounds in about nine months. However, if you're only willing to workout out three days per week, the process may take you 12+ months. There are other factors to consider, of course, and this is just one example fo context.
The meso and micro cycles are partially determined based on your macro cycle length, and the training preferences of the coach. For example, if you have a 12-month macro cycle, the meso cycle might be 12 weeks, and the micro cycle three weeks. However, the meso could easily be six weeks and the micro one week.
Your goals and the given training methodology needed to reach them partially dictate the cycle length as well. For example, 3- to 16-week meso and/or micro cycles are very common in powerlifting, while 1-6 week meso and/or micro cycles are common in Olympic weightlifting, and running might call for meso and/or micro cycles 8-20+ weeks in length.
Why such variation? Often it comes down to coach preference. Some coaches don't follow a specific training cycle, and instead have a "train by feel" approach, in that they base programming for the week on how the trainee performed in previous weeks, Olympic coach Mike Bergener has been noted as using this approach for newbies. Performance coach Dave Spitz leans toward 4- to 6- week training cycles. Hal Higdon, a running coach, lists programs 8- to 18-weeks in length on his websites.
What do we use at Nathan DeMetz Personal Training? It depends on if we're creating a program for clients or for us. For ourselves, we have a 12-month macro cycle, 13-week meso cycle, and a three-week micro cycle (and each week is kind of a micro-micro cycle). We plan out our year in advance, understanding that changes will need to occur, and we follow a basic structure adjusting as needed over the course of the year.
The approach is different with clients. Ideally, we would like to create a 12-month program for each client, but this is not practical, since at least half of clients will not stay in training for a year. Instead of the one-year approach, we take a 12-week approach. The macro cycle is 12 weeks, the meso is 2-4 weeks, and micro is one week.
Regardless of the approach used by the trainer, each coach looks at the goals and situational factors of the client to create a program that fits his or her needs. Knowing how to do this comes from education and experience. If you're not a trained coach, then the best approach for you is to work with a trainer or coach, or to find a free or purchase program from such as an individual or from sites such as demetzonlinepersonaltraining.com, catalystathletics.com, bodybuilding.com, halhigdon.com, trainheroic.com, or www.jtsstrength.com.