If there's one thing that CrossFit has shown us, it's that humans can demonstrate respectable levels of both strength and endurance at the same time.
Athletes who compete in sports such as rugby and soccer also demonstrate admirable levels of strength and muscle size whilst enduring sometimes hours-long competition on the field.
Most sports require the combination of several components of physical fitness in varying degrees.
Therefore athletes frequently train to develop several components of fitness simultaneously to improve sports performance. However, if you're trying to become more "fit" by multiple measures simultaneously, there are some things you should know.
The Typical CrossFit WOD
CrossFit encourages the training of several components at once, often within the same workout or "WOD."
For example, here's the workout "MURPH":
- 1-Mile Run
- 100 Pull-Ups
- 200 Push-Ups
- 300 Bodyweight Squats
- 1-Mile Run
And here's "JACKIE":
- 1000-Meter Row
- 50 Thrusters
- 30 Pull-Ups
And here's "DIANE":
- 21 Deadlifts
- 21 Handstand Push-Ups
- 15 Deadlifts
- 15 Handstand Push-ups
- 9 Deadlifts
- 9 Handstand Push-ups
As you can see from some of the most popular workouts, these WODs are training multiple capacities at the same time. Proponents suggest that such workouts can encourage gains in strength and endurance simultaneously, along with positive changes in body composition.
Structured periodization is also not a typical feature of CrossFit training, so these capacities are often being trained at the same time on the same day throughout the entire year. By training it all at once, it's suggested that you can indeed have it all. Unfortunately, however, it may not be that simple.
What is Concurrent Training?
The term concurrent training is used to describe strength training and endurance training within the same training cycle. Team sport athletes have been training this way for years as their sport demands it, but more recently, it has become popular in mainstream gyms and CrossFit boxes.
Endurance training should not be thought of as just the ability to run a marathon. We can see concurrent training as both aerobic and anaerobic endurance, and most forms of training that have a high metabolic demand.
Despite the popularity of this type of training, most studies on concurrent training have produced contradictory results, with some showing complementary effects (Mikkola et al. 2007a, 2007b), some displaying inhibiting effects (termed the interference phenomenon) (Bell et al. 2000., Cadore et al. 2010) and some showing no difference between concurrent and strength or endurance training (Glowacki et al., 2004).
Since this type of training is becoming more popular, it's important to understand its potential benefits and drawbacks, both for sports coaches looking to train multiple capacities at once, and those involved in CrossFit training.
We can't talk about concurrent training without mentioning the SAID principle.
SAID stands for Specific Adaptation to Imposed Demands. In short, the body will adapt in accordance to the training demands that have been placed upon it.
Take another look at the popular WODs above.
Is the purpose of each workout to improve maximal strength or power, stimulate hypertrophy, or develop endurance?
If you had to pick one thing, most would say they're training endurance, but the truth is that there's a blend of demands there.
Specificity of training denotes that prolonged endurance training enhances aerobic performance by enhancing maximal oxygen uptake, improving muscle aerobic enzyme activities and increasing capillary and mitochondrial density of the muscles.
On the other hand, typical heavy-load strength training results in neural and muscular adaptations responsible for improved strength, power and muscular size.
The physiological stimuli directed to skeletal muscle as a result of strength training and endurance training are therefore quite different and contrasting in nature.
However, while too much endurance training hampers strength/power development in concurrent training, it seems that direct strength/power training doesn't have the same impact on endurance.
Mechanisms of Interference
Most of the research has supported the idea that adaptations to strength training are limited when combined with endurance training.
The physiological basis for this may be linked to several factors, including an elevated catabolic hormonal state, low muscle glycogen levels, changes in muscle fiber composition, greater increases in the capillary to fiber ratio, and impaired adaptive responses in protein synthesis.
One mechanism of interference more recently talked about is that of the interaction between MToR (Mammalian Target of Rapamycin) and AMPK (AMP-Activated Protein Kinase). These enzymes are important for regulating the initial responses involved in both strength and endurance training.
A simplistic view of these enzymes is that once activated, mToR can initiate muscle growth and strength gain, along with other adaptations associated with heavy-load strength training. AMPK, on the other hand, which is activated in response to endurance training, or training with a high metabolic demand, can act to "switch-off" MToR.
It's interesting to note that MToR activation does not affect AMPK. Again, in a simplistic view of things, this means that endurance exercise can affect strength training adaptations, but strength training does not affect the initial adaptations to endurance training.
This biochemical response may be one of the reasons why strength training may work well to help improve the performance of endurance athletes, but endurance training does not have a complementary effect on maximal strength or size development.
Based on this theory, an endurance athlete will benefit from some strength training, while a strength/power athlete should be careful about the amount of time he or she devotes to endurance exercise.
For those interested in maximizing the anabolic response to training and promoting muscle growth, endurance exercise should be kept to a minimum. Docherty and Sporer (2000) hypothesized that interference would be greater when an athlete combined a hypertrophy training protocol with an endurance protocol than it would a pure strength-building protocol combined with an endurance protocol.
This is because the training stimulus for increases in strength rely more on changes in the neural system than the training stimulus for increases in hypertrophy, making them less susceptible to interference from aerobic-driven adaptations.
Concurrent Training Recommendations
The reality is that many people want to have it all.
They want to increase their strength, power and endurance all at once. While we know that some adaptations may be compromised when trying to develop both strength and endurance at the same time, development in both areas can be seen provided certain rules are adhered to.
These rules are applicable to strength/power sport and physique athletes only, whilst endurance athletes such as marathon runners will have a different set of rules.
In untrained or moderately trained individuals, strength gains seem to be similar between strength and combined strength and endurance groups when the number of exercise sessions per week is three or four. Therefore, ideal frequency of concurrent training should include two to three strength training sessions, and one to two endurance training sessions per week.
More than this frequency may inhibit recovery, while less may not provide adequate volume to invoke adaptations. The duration of each endurance session should also come into play, as well as any sport practice included within the week (for team sport athletes, practices are often "endurance" exposures).
Each session should prioritize either strength or endurance adaptations, while a "WOD"-style mixed approach may not be ideal.
A "beginner" weekly schedule for concurrent training may look something like the following:
- Monday: Full-Body Strength Training
- Tuesday: Endurance/Metabolic Conditioning
- Wednesday: Off Day
- Thursday: Full-Body Strength Training
- Friday Endurance/Metabolic Conditioning
- Saturday: Off Day
- Sunday: Off Day
In more experienced athletes, strength training frequency can be higher, while endurance training frequency should remain limited to two sessions a week unless endurance and conditioning become a bigger priority.
An "advanced" weekly schedule may look something like the following, depending on sport competition and several other factors:
- Monday: Lower-Body Strength Training
- Tuesday: Upper-Body Strength Training
- Wednesday: Endurance/Conditioning
- Thursday: Lower-Body Strength Training
- Friday: Upper-Body Strength Training
- Saturday: Endurance/Metabolic Conditioning
- Sunday: Off Day
Low repetitions and higher intensities should be used to invoke mainly neural adaptations, such as increased number of active motor units and/or an increase in their firing frequency rates.
If the goal is to build maximum muscle, then the mix of higher volume strength training and endurance training is not a good combination. To develop lean muscle tissue, endurance training should be kept to the absolute minimum and be used for health purposes only.
It's important to note however, that in research on concurrent training involving previously untrained adults, training loads conducive to hypertrophy (67-85% of one-rep max) did result in some strength development (though little actual hypertrophy). This is because the increases in maximal strength observed during the initial weeks of strength training can be attributed largely to neural adaptations.
So for untrained individuals, a hypertrophy training protocol combined with endurance training could develop strength, but the strength-boosting effect of such a protocol will likely disappear after the first few months of training. Thereafter, larger loads and lower reps should be utilized.
When trying to develop multiple capacities simultaneously, it's important to consider the signals we're sending to our body.
If you're a trained athlete, and strength, power and/or hypertrophy are most important to you, then it's probably best to concentrate on those areas while performing little to no dedicated endurance work.
If aerobic endurance is paramount, then adding a bit of strength and power work to your routine is unlikely to decrease that trait, and it may even boost your performance.
If strength training and endurance training are combined within the same training cycle, it would be wise to complete separate workouts to train each capacity (ideally with each workout falling on different days) rather than try and achieve it all at once within the same workout.
If you want to train to have it all, training it all within the same workout may not be the best way to go.
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