Periodization philosophy is largely based on the fact that adaptations to physical exercise can be predicted and that it follows a determinable pattern, which can be problematic. The genotype-VO2max related Heritage Family Study as well as other studies looking at resistance training-focused interventions show several examples of how one exercise protocol can result in a wide range of responses in different populations and different subjects.

In the Heritage Family Study, an endurance training protocol was able to increase the average VO2max of the subjects by 19%. However, 5% of the participants saw no change in their VO2 values, while another 5% saw an increase of up to 50%. In a resistance training intervention, 12 weeks of a strength training program saw a 54% average increase in strength. The "non-responders" saw no increase in strength while more highly sensitive responders saw a 250% increase. 250%!!

Training adaptations are not only mediated by the training program itself (assuming adherence to the training protocols are close to 100%), but by other factors such as initial training age of the subjects, nutritional and dietary habits/protocols, recovery and restoration of the athletes (are they sleeping enough?), and exercise technique.

Initial Training Experience and Age of the Subjects

Like I alluded in the earlier articles, the initial fitness or training experience of a subject plays a factor in the results we expect to see after prescribing them a training protocol. Because novice and beginner trainees have low initial functioning performance measures, research studies focused on periodized training programs are unable to discern which periodization model works better for this population. When you're a beginner, almost everything works!

For example, in the realm of concurrent training (strength and endurance training together and their interaction), untrained individuals are usually able to increase both their strength and endurance performance with minimal interference between the 2 modalities. Trained individuals on the other hand, experience a greater interference effect when performing concurrent training: endurance training diminishes the adaptations of their resistance training and vice versa.

Nutrition and Dietary Protocols, Recovery & Restoration.

Nutrition has a large impact on training outcomes and adaptations. The fact that some strength, endurance or periodization studies don't account for dietary intake is problematic. For example, if protein intake is not controlled for in subjects of a strength training based research study, no amount of program-periodizing can come to any consistent conclusions about periodization and muscle strength or hypertrophy. I've written about nutritional periodization in detail here - check it out.

Recovery and rest obviously play a big role in the training process as well as it directly affects training performance, fatiguability of the athlete, and at the end of the day, determines how much progress they'll be able to make.

Exercise Technique

This is a variable that is often overlooked in research studies looking at the effects of periodization on strength in particular. Athletes and subjects that possess more biomechanically efficient lifting technique have a higher ceiling for strength acquisition, therefore may experience greater strength gains on any given training program. Subjects that are inexperienced, or have glaring flaws in their lifting technique are not able to reap in the full benefits of a periodized plan as their technique acts as a bottleneck for progress.

There is no quantitative way to assess lifting technique, therefore it is a variable that is hard to control in a research setting. I'm a firm believer that the execution of the lift, or of training itself, is very important in order to get the most out of a training plan.

Due to the practicality and perhaps lack of research funding, many of these variables I've discussed above are not taking into account when researchers design a study looking at different periodization models. Take these research study results with a grain of salt and remember: principles are always better than rigid, inflexible methods and systems.