“They are like oil and water.” Every so often, those are the words we use to describe two people who don’t get along, two people who are incompatible. Within strength and conditioning, some studies indicate that strength training and endurance training are like oil and water. These studies indicate that if you plan developmental training of both these components at the same time, one or both components will suffer. However, other studies indicate that strength training and endurance training might be compatible and that the ultimate cause of incompatibility might be overtraining (4).

For a strength coach, the possibility that the effect of strength training and aerobic training may cancel each other out can be problematic. Many sports, including team sports, martial arts, and racquet sports, require substantial levels of many kinds of strength as well as energy systems conditioning. On top of that, often there is only limited time to develop these physical qualities.

With the flexible periodization model, the goal was to develop a method of periodization that can be used effectively for all sports, thus the area of developing multiple bio-motor abilities (strength, power, speed, endurance, and flexibility) simultaneously is a really important part of the method.

There are some fundamental aspects that relate to the simultaneous development of multiple bio-motor abilities:

  • In some sports, the goal is to maximally develop a certain bio-motor ability. A prime example is the development of maximal strength for the powerlifter.
  • In other sports, the goal is to optimally develop a certain bio-motor ability. For example, an MMA athlete is satisfied with an optimal development of maximal strength together with optimal development of power and aerobic and anaerobic power and capacity.
  • In some cases, the goal of training multiple bio-motor abilities within one week of training is to use one type of training to create an immediate improvement of another bio-motor ability. For example, stretching the hip flexors can have an acute facilitating effect on vertical jump performance (5). (Note: When we say that “stretching inhibits strength and power,” we have to add that it depends on the relationship between the muscles being stretched and the role that those muscles play in the movement. While stretching the agonist may inhibit strength/power, stretching the antagonist may increase strength and power.)
  • Athletes who simultaneously train strength and endurance (i.e. endurance sports) use the strength training to improve the endurance. They don’t care if they get stronger. They're interested in strength training to improve their endurance performance.
  • Athletes from the endurance sports, racquet sports, martial arts, and team sports seek to simultaneously develop multiple bio-motor abilities. The MMA athlete wants to get stronger and more powerful and have greater endurance all at the same time.

Any strength coach should be interested in creating and exploiting synergistic effects to make the whole more than the sum of the parts. With respect to the development of multiple bio-motor abilities in the same week, one of the first questions I asked was what it would take to create synergy between strength training and energy systems training or at least minimize or avoid any negative interactions. Programs containing simultaneous training to develop multiple bio-motor abilities (i.e. strength training and aerobic training) are called “concurrent training” and have been investigated in training literature. The following section reviews some of the findings from the research literature.

Study #1

Twenty college students with below to above average fitness levels in long jump performance were assigned to one of two groups that trained for 45 minutes twice a week for thirteen total weeks. The sequence in which these modalities were executed isn't reported in the study.

  • Strength plus endurance group (SE): This group performed strength training (5–20 RM) with flexible, non-linear periodization (doesn't have anything to do with the flexible periodization method) plus low intensity cycling.
  • Strength plus endurance plus high intensity cycling group (SEC): The high intensity cycling group added two 15- to 45-second maximal intensity cycling intervals per workout.

Results: Chest press and standing broad jump were tested before and after the training. Both groups showed significant improvements except for the SE group in the long jump.

Discussion: According to the authors, there weren't any significant effects on the standing broad jump and chest press from adding intense, anaerobic glycolytic training to the strength and endurance program. The strength program was predominantly machine based, and the authors conclude that the SE group may not have performed sufficiently “explosive” contractions to stimulate the standing broad jump. It can be speculated that there would have been a significant difference between groups if the outcome measure (what was tested) had been cycling. The authors further discuss that “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.”

Take away message: Athletes of lower qualification don't need extensive volume and intensity to improve in strength. In this case, the athletes were able to improve strength despite the endurance training (however, strength gains might have been more pronounced if there hadn't been any endurance training). The principle of specificity is important to apply in relation to your outcome variables. For example, there might have been a significant difference in the two groups in the chest press if arm cycling had been used for the high intensity intervals. Further, body weight squats and standing broad jumps should have been used in the training if the goal was to improve broad jumps. If your athletes aren't ready for complex free weight exercises, don’t give them machine-based exercises. Instead, start them on simple body weight exercises.

Training on the Schwinn Airdyne could potentially have caused transfer from the high intensity intervals to the chest press. Battling ropes are another example of an upper body dominant exercise that can be performed at high intensity intervals with a potential transfer to upper body strength. This probably isn't the case with the bench press though.

Study #2

Heavy resistance training (70–80 percent 1RM) performed immediately after endurance training (consisting of one hour at 65 percent of V02max) results in enhanced expression of genes involved in mitochondrial biogenesis/oxidative metabolism in recreationally active subjects.

Discussion: This effect appears to be mediated by the intensity of training. The authors can't exclude that the same results would have appeared with high intensity cycling. This effect isn't seen if endurance and resistance training are performed on separate days. The authors argue that these results can be explained with “cross talk” between bio-chemical pathways, but due to the design of the study, they weren't able to say if it was an effect of the resistance training or a synergistic effect (2).

Take away message: The timing of specific components can be critical to achieve the desired training effect. If you're training any athlete who performs low intensity endurance training, it can be beneficial to perform strength training right after the endurance training. Note: The focus here is to use strength training to improve endurance performance. The study says nothing about the effect on strength development.

I've seen great results for cyclists by combining standard leg presses with leg presses using only one leg.

Study #3

A large review (meta-analysis) of studies on concurrent training offer the following guidelines (1):

  • Endurance training modality is a primary factor in determining interference. Running but not cycling results in negative effects on both strength and hypertrophy in the concurrent training group. This difference could be caused by cycling being more specific to the applied tests as well as less muscle damage caused by cycling compared to running.
  • Shorter duration and higher intensity interval training doesn't result in decrements in strength and power and can result in significant improvements in V02 max.
  • Interference effects are body part specific, not systemic. Decrements in strength are seen in lower body but not upper body exercise after lower body-oriented endurance exercise.
  • Volume accounts for a relatively small portion of any interference effect seen on strength, power, and hypertrophy.
  • Power is more susceptible to decrements than strength or hypertrophy. The researchers suspect that the effect is through an attenuation of (contraction) velocity or rate of force development.
  • V02 max isn't negatively affected by concurrent training, and endurance performance could even be augmented by an increase in the area of type 2a fibers and a gain in maximal muscle strength and rate of force development.
  • With regards to fat loss, running as well as higher intensity training results in the largest reduction in fat.
  • Moderate intensity endurance training performed (immediately) after strength training can blunt protein synthesis for the duration of the activity.

The authors offer two main hypothesis for the trends seen—1) overreaching and overtraining and 2) competing adaptations from endurance training versus strength training. 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:

  • Endurance training: Low force outputs and longer duration
  • Strength training: Near maximal or maximal force outputs and short durations

Strength training predominantly increases protein synthesis in the myofibrillar subfraction (of the muscle cell) while endurance training predominantly increases protein synthesis in the mitochondrial subfraction. Strength athletes show an increase in type 2 fiber size and a decrease in mitochondrial density relative to the average population. In contrast, endurance athletes show an increase in mitochondrial density without any or a small selective increase of type 1 fibers.

Strength training and low intensity endurance training are mainly characterized by competing adaptations. However, low intensity endurance training and strength training have commonalities with high intensity endurance training (sprints/intervals).

Take away message: Athletes whose sports require maximal strength, maximal power, or rate of force development should limit concurrent strength and low intensity endurance training and focus on high intensity endurance training. If the athlete’s sport is based on strength and hypertrophy, concurrent strength and endurance training are less problematic. Endurance modalities should mimic the sport as closely as possible. If fat loss is the main goal (higher priority than strength and hypertrophy), running should be chosen as the endurance modality.

In this article, I reviewed some of the research on concurrent training with the inclusion of directly applicable take away messages. In my next article, I'll discuss in detail how the information discussed here has shaped a key principle in the flexible periodization method.


  1. 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):2293–07.
  2. Wang L, Mascher H, Psilander N, Blomstrand E, Sahlin K (2011) Resistance exercise enhances the molecular signaling of mitochondrial biogenesis induced by endurance exercise in human skeletal muscle. J Appl Physiol 111:1335–44.
  3. 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.
  4. Fleck SJ, Kraemer WJ. Integrating other fitness components. In: Designing Resistance Training Programs, Chapter 4. Human Kinetics, pg 135.
  5. Sandberg JB, Wagner DR, Willardson JM, Smith GA (2012) Acute effects of antagonist stretching on jump height, torque and electromyography of agonist musculature. J Str Cond Res 26(5):1249–56.

The Flexible Periodization Method