I'm strongly attracted to principles and ideas because good principles and idea can be your guides in many different situations. In the first part of this article series, I mentioned the idea that any strength coach should be interested in creating and exploiting synergistic effects to make the whole more than the sum of the parts. Even if you disagree with everything else in this column, the single idea of seeking out synergistic effects between various aspects of the training program can be of immense value to you.

Asking the right questions is another fundamental skill that can help you operate at the highest level possible. In part 1, we looked at what research studies had to say with respect to the question, "What would it take to create synergy between strength training and energy systems training or at least minimize or avoid any negative interactions?”

In this article, part 2, I'll discuss how the conclusions from part 1 are used in the flexible periodization method. The absolute key conclusions that form the basis for how the flexible periodization method creates synergy between strength training and endurance training are found in the following quotes. “The unique physiological and chemical interactions that exist when varied and multiple exercise stressors are placed on a subject can be highly complex and interrelated. There may need to be a particular alignment of training variables and a very small window of opportunity within which a SEC program is effective” (1).

"Overreaching and overtraining appear to play a smaller part of the negative effects seen in the reviewed studies. The competing adaptations are related to differences in duration and force levels between endurance training and strength training (2). Endurance training consists of low force outputs and longer durations, and strength training consists of near maximal or maximal force outputs and short durations.

The key words from the two quotes are, “There may be a particular alignment of training variablesand a very small window of opportunity (within which an SEC program is effective).” The key words from the second quote are, “The competing adaptations are related to differences in duration and force levels between endurance training and strength training.”

If competing adaptations (between strength and endurance training) are related to differences in force levels and duration, we can hypothesize that synergistic adaptations would come about with similar force levels and duration. To be slightly more specific, the flexible periodization method aligns the length of the set with the length of the interval. Clearly, endurance athletes will need continuous work beyond the length of resistance training sets. In addition, other athletes from interval-based sports might, in some rare situations, benefit from continuous endurance training.

By aligning the length of the set with the length of the interval, we ensure that the duration of work is the same, but we can't ensure that the force levels, and thus the mechanical stress, are exactly the same. For example, let’s say that a set of five reps with a 5RM load takes twenty seconds—five contractions in twenty seconds. Compare that to a twenty-second all out sprint on a row ergometer that could involve twenty or more contractions in the same time frame. We can’t say that the force levels will be the same in the set of barbell back squats compared to the row ergometer, but we can say with great certainty that they will be more similar than if we had compared the set of barbell squats with twenty minutes (or more) of continuous rowing.

The principle of aligning the length of the resistance training set with the length of the interval is applied in situations where it is the goal to optimally (possibly maximally) develop both the strength component and the speed/energy systems component of training. The principle isn't necessarily applied in situations where it is the goal to use resistance training to improve endurance performance.

Seven fundamental training methods

The actual length of a set and an interval depend on the goals of that set in terms of strength and energy systems. Regarding strength training, jumping and throwing, speed energy systems, and cardiorespiratory training, the flexible periodization method includes seven fundamental training methods. The flexible periodization method employs the terminology “jumping and throwing” instead of plyometric training because the plyometric effect is present in most resistance training unless the athlete pauses for four seconds or longer between the eccentric and concentric phase (3). In addition, where some texts use the terms “aerobic/anaerobic training” or “energy systems training” (or in the fitness realm, “cardio”), the flexible periodization method uses the term SEC—speed, energy systems, and cardiovascular training. Why has the flexible periodization method adopted the acronym SEC instead of something like aerobic/anaerobic training? Some athletes perform this type of training mainly for speed. Other athletes perform it mainly for the effect on the energy systems. Fitness clients who have been told by their doctors that they could get a heart attack if they don’t start training use this training for the cardiovascular benefits. With the SEC acronym, the flexible periodization method wants to embrace these three main reasons for performing that type of training.

Repeated effort method

The textbook definition of the repeated effort method is “to use submaximal loads to failure or near failure” (4). The following section discusses the physiological basis for distinguishing between the repeated effort methods of long and short duration.

The heavy chain of the myosin molecule (MyHC) exists in three different forms—MyHCI, MyHCIIA, and MyHC IIX—that endow the muscle fiber with specific functional characteristics such as contraction speed and metabolic characteristics. Because the content of myosin heavy chains forms the basis for the functional characteristics of the fiber types, the three types of myosin heavy chains are reflected in the classification of fiber types. Thus, the fundamental fiber (pure) types are Type I (slow twitch), Type II A (fast twitch), and Type II X (formerly type II B and also fast twitch) (6). In human skeletal muscle, there is often more than one type of myosin heavy chain present in the same fiber, which gives rise to hybrid fibers that exist in a continuum from slow and most oxidative to fast and least oxidative (5, 6).

This continuum is reflected in an approximation of time to exhaustion during “optimal tension” and recovery for the three pure fiber types (see the graph below). The most oxidative fibers (type I) have the greatest endurance and the last oxidative fibers have the least endurance.


Force loss and recovery as a function of time under tension for type1, type IIA, and type IIX fibers (7).

While it is important to maintain that the numbers are approximations, the graph offers the following pattern to serve as guidelines (7):

  • It takes up to 3–5 minutes of loading with “optimal tension” to exhaust the type I fibers.
  • It takes up 30–120 seconds of loading with “optimal tension” to exhaust the type IIA fibers.
  • It takes 3–15 seconds of loading with “optimal tension” to exhaust the type IIX fibers.

Based on the graph, we can see that in sets with less than 120 seconds of tension, the type IIA fibers still contribute to the force production. Thus, when the focus is to challenge the endurance of the type I fibers, it is necessary to maintain tension for a duration that exceeds 120 seconds.

We would surely expect the type I fibers to be activated also in shorter sets. However, the type I fibers might be compared to a marathon runner after a 100-meter race. Yes, the marathon runner participated in the race, but the short race didn't challenge the marathon runner on his peak competencies, which is endurance.

Why would we be interested in the type I fibers that are neither the strongest nor the fastest fibers? One of the principles of the flexible periodization method is to develop endurance of (tonic) stabilizer muscles before strength of the prime movers. The focus is the smaller stabilizers that are situated closer to the joint, characterized by tonic activity and resistance to fatigue. Even though there are individual differences, we can hypothesize that these small stabilizer muscles—as a general rule—have a large proportion of type I fibers.

The main purpose of the repeated effort method in the flexible periodization method is to develop endurance of these small stabilizer muscles with sets of 2–5 minutes in duration. Before you start to visualize pink dumbbells, consider this quote:

“The sportsman finds himself under the weight for 2–3 minutes. The entire body must sustain this prolonged effort as the athlete completes several consecutive exercises without letting go of the equipment. The weight of the barbell is relatively light, but the varied work with it affects every muscle cell.” — Vasily Alexejev, 80 times world record holder in Olympic weightlifting

The flexible periodization method uses combination exercises (complexes) and single joint or multi-joint exercises to place key stabilizers under tension for 2–5 minutes. Watch this video for an example of such a complex with three deadlift variations that might be done for 12 + 12 + 12 repetitions.

Stay tuned for part 3 where I'll cover the rest of the fundamental training methods and how they are used in the flexible periodization method.


  1. McNamara JM, Stearne DJ (2013) Effect of concurrent training, flexible nonlinear periodization and maximal effort cycling on strength and power. J Strength Cond Res 27(6):1463–70.
  2. Wilson JM, Marin PJ, Rhea MR, Wilson SMC, Loenneke JP, Anderson JC (2012) Concurrent Training: A meta-analysis examining interference of aerobic and resistance training exercises. J Strength Cond Res 26(8):2293–2307.
  3. Wilson GJ, Elliot BC, Wood GA (1991) The effect on performance of imposing a delay during a stretch-shortening cycle movement. Med Sci in Sports and Exerc 23(3):364–70.
  4. Zatsiorsky W (1995) Science and Practice of Strength Training, 1st ed. Human Kinetics, pgs 102–105.
  5. Andersen JL, Aagaard P (2010) Effects of strength training on muscle fibre type and size, consequences for athletes training for high intensity sport. Scand J Med Sci Sports 20(S2):32–38.
  6. Hunter GR, Harris RT (2008) Muscular, Neuromuscular, Cardiovascular and Respiratory Systems: Essentials of Strength Training and Conditioning, 3rd Edition. Human Kinetics,  pg 9.
  7. Telle J. Muscle Fibre Fatigue and Recovery. Beyond 2001. The Next Real Step. New Approaches to Scientific Training for the Advanced Bodybuilder. Denver, Colorado, pg 192.