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By: Alex Hoffmann
I'll be honest: early on in my training career I didn't really know what I was doing. My personal training skills consisted of coaching basic exercise technique, yelling out words of encouragement, and making sure that every client I trained worked up a good sweat by the end of the training session. Training with me in my early days was the equivalent to training with a very mediocre (at best!) fitness DVD. While my clients usually received some general body composition and fitness improvements from this technique, I started to feel very inferior and bit like a fraud as a trainer - and rightly so. I could get people "in-shape," but I didn't know how to improve their performance.
I didn't even realize this until a client asked me "Why?" after an exercise I gave him. If I prescribed a squat for 4 sets of 8 repetitions he would ask, "Why am I doing this instead of a squat for 5 sets of 3 repetitions?" If I prescribed a moderately paced 3-mile jog on a day we weren't training together, he would ask, "Why am I doing this instead of 400 meter intervals?"
I was frustrated with his questions, but what was really bothering me was the fact that I couldn't provide a satisfying answer - for him or me. I would usually ramble off something totally uninformed (and unprofessional) like, "Well, this is how (fill in your favorite athlete, model, bodybuilder, celebrity trainer, etc.) trains, so it clearly works." Or, "This is what my college strength coach had the football team do." Or worst of all, "It worked for me, so it will work for you too."
These were very embarrassing conversations for me to have as a young, inexperienced professional. Even writing or talking about it now is uncomfortable as a I recall how poorly prepared I was to give meaningful answers to legitimate questions from a person who trusted me with their physical fitness. However, I share my experience with you so you do not have to go through the same thing.
Know the science - it's your friend! As professional trainers, the initial prescriptions we make should be the result of our own review of scientific data. We don't need to read every piece of published scientific literature; this would be extremely time-consuming and, frankly, really boring. We do need to have a firm understanding of how to apply major pieces of research to achieve specific results. Would you a want a doctor to give you a medication because they saw that it works on an infomercial? Of course not! We expect our doctors to have reviewed the medication's clinical trials and know that it will make us healthier in the way they say it will. In this same manner, our clients expect us to have a basic understanding of exercise science research before we give them an exercise program.
Let's apply this to a very common question:
Or more accurately, should we perform steady-state aerobic training and resistance training in the same training cycle (often referred to as concurrent training)?
Resistance training and steady-state aerobic training both provide fantastic benefits. However, some of the physiological changes caused by resistance training are in direct opposition to those caused by aerobic training and vice-versa. For example, strength training promotes gains in strength, power, and hypertrophy (increase in muscle size) but promotes a decrease in mitochondrial density (a key factor in one's aerobic endurance capacity). On the other hand, steady-state aerobic training increases the oxidative capacity of the muscle (the extent to which muscle can make use of oxygen) but promotes a decrease in maximal power output and a possible decrease in Type II (fast-twitch) muscle fiber size. You can read the research that proves this - or just put a marathon runner and powerlifter next to each other. I'm confident you'll see the differences.
This has led to the popular belief that concurrent training leads to "adaptation interference," meaning that the benefits of one training mode are negated by the other when performed in the same training cycle, and preventing the individual from receiving maximal benefits from the training program.
This belief is supported: a study performed in 1980 by RC Hickson demonstrated this idea. Over 10 weeks, three exercise groups followed three different programs: a strength training only group (S) trained 5 days per week, an endurance training only group (E) trained six days per week, and an S and E training group (concurrent training) performed the same daily exercise regimens as both the S and E groups. The results of the study showed that the S-only group had significantly greater strength gains than those in either the S and E (concurrent training) group or the E-only group. Surprisingly however, the group performing the concurrent training program showed equal improvements in VOmax (or maximal oxygen uptake, which is a measure of how much oxygen your muscles can suck out of your blood and use. It's really, really important to athletic performance) when compared to those in the E-only group.
The relevant question is whether concurrent training always interferes with resistance training adaptations. If my goal is to improve strength and power, do I need to avoid aerobic training at all costs? Is there ever a time when concurrent training will benefit an individual or athlete looking to receive positive adaptations from resistance training? Fortunately, there's more science to answer those questions! An analysis of 21 studies on concurrent training conducted in 2012 by Wilson et al. revealed some very interesting data on this subject.
Power (the ability to generate force quickly) is the major performance variable that is negatively affected by concurrent training. Strength training alone allowed for significantly greater power development when compared to strength training concurrently with aerobic training.
Strength training alone allowed for significantly greater strength and hypertrophy gains in the lower body when compared to strength training concurrently with aerobic training. However, this only occurred when the aerobic exercise modality was running.
Cycling concurrently with strength training did not significantly affect lower body strength and hypertrophy gains when compared to strength training only.
Regardless of the aerobic training modality choice, strength and hypertrophy gains of the upper body were unaffected by concurrent training when compared to strength training only.
Total volume of aerobic training is likely a determining factor in whether or not concurrent training significantly negates strength, power, and hypertrophy gains. Aerobic training three days per week or more for longer than 20-30 minutes led to more interference with strength, power, and hypertrophy gains than a lower volume of aerobic training.
Concurrent training led to a significantly greater reduction in body fat percentage when compared to strength training alone or endurance training alone.
One important note, the studies reviewed in this meta-analysis did not investigate the relationship between High Intensity Interval Training (HIIT) and strength, power, and hypertrophy gains. It is generally acknowledged that HIIT will not negatively affect these resistance training adaptations and may even enhance them. For more information on this topic check out this terrific article by Mr. Josh Bryant and Dr. Fred Hatfield).
The analysis above shows us that concurrent training only creates significant adaptation interference under certain conditions. Once a base level of fitness has been established, the following guidelines derived from this analysis will help to ensure that you and your clients are able to avoid this interference effect.
If the client's primary goal is to improve power (e.g. improving sprint speed, vertical jumping, Olympic Lifting, etc.), long duration/low intensity aerobic training should be kept to a minimum.
If the client's primary goal is to improve strength and/or hypertrophy and he/she wishes to train concurrently with aerobic training, it is best to keep the duration of aerobic training to less than 30 minutes and the frequency of aerobic training to fewer than 3 days per week. Furthermore, a low-impact mode of aerobic training such as cycling or rowing appears to be a more appropriate option than running.
If the client's primary goal is fat loss, concurrent training should be encouraged as it produces a greater reduction in body fat percentage than either strength training alone or aerobic training alone.
If the client's primary goal is to improve aerobic performance, concurrent training is advisable as resistance training has not been shown to significantly interfere with aerobic capacity gains.
Our responsibility as professional trainers is to make exercise prescriptions that are rooted in scientific research, but the guidelines are not the final word on how to design a program. Rather, they are a starting point to consider, from which adjustments can be made based on progress and individual needs. All bodies are different, and certain individuals will undoubtedly react more negatively to concurrent training than others. However, the interference effect is a variable that we as trainers must be aware of, especially when we start to work with advanced trainees. The name of the program design game is specificity. The more specific we can make our program design to our client's performance objective, the greater our clients' chances of success!
Want to enhance your training even more? Sign up for ISSA's Certified Fitness Trainer course to learn all of the essentials in building top-notch programs for strength, weight loss, and a variety of other health and fitness goals.
Hickson, R. C. (1980). Interference of strength development by simultaneously training for strength and endurance. European Journal of Applied Physiology and Occupational Physiology Europ. J. Appl. Physiol., 45(2-3), 255-263.
Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent training: A meta-analysis examining interference of aerobic and resistance exercises.Journal of Strength and Conditioning Research, 26(8), 2293-2307.
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