Interference Effect: Why Endurance and Strength Training don’t Mesh by Jared Ogan

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[This is a guest blog by Jared Ogan. Jared has a B.S in kinesiology from the University of Central Oklahoma, is a USAW-L1 performance coach, and is an athletic development intern at Athletic Lab.]

Throughout my athletic career, I’ve always had a stronger aerobic system. I’ve been better at the sports that require my body to transport oxygen to the parts of my body that needed it; like distance running or soccer. I am not sure why, I have just always felt more comfortable running longer distances than doing sprints. I am sure some people can relate. As I have aged and gotten away from the 50 to 60 miles of running per week, I have come to appreciate lifting and building muscle. My enjoyment of running has never left, and has always been my go to exercise when wanting something simple but efficient to do. What about pairing them together? Why not be a good runner and work to be muscularly strong? Seems like the perfect answer, exactly what I want. Not entirely.

Interference Phenomenon

interferenceThere is a phenomenon known as the interference effect that occurs when pairing endurance and strength training together, one right after the other. This is also known as concurrent training. One conclusion people have made about the interference effect is that when performing concurrent training, your strength gains will be compromised by the simultaneous training of aerobic power (1). People hypothesize that the strength gains are compromised because concurrent training results in excess fatigue, a greater catabolic state, differences in motor unit recruitment patterns and a possible shift in fiber type (1). Your body is trying to adapt to both forms of exercise. This is not possible because adaptations to endurance training are often inconsistent with adaptations observed during strength training (2). An article published in the Journal of the American Physical Therapy Association states, “endurance training induces increases in mitochondrial content, citric acid enzymes, and oxidative capacity. There can also be increases in slow-twitch fiber area and possibly even a conversion of fibers from fast-twitch to slow twitch. Strength training, however, will reduce the mitochondrial density and induce relatively small increases in oxidative enzymes. Increases in myokinase (adenylate kinase) activity and fast-twitch fiber area have also been seen.” (3) The question that comes to mind is what can we do about training both endurance and strength with this interference effect?

Let’s first cover this interference effect and what adaptations take place after concurrent training. As previously mentioned, endurance and strength training have their specific adaptations that take place with their specific training prescriptions. Most of the research out there usually has three to four experimental groups: an endurance training only group, a strength training only group, a concurrent training group, and possibly a control group. The results usually are that each type of training performed individually will see greater results than combining the two types of training. Endurance training will see greater increases in maximal oxygen consumption (VO2 max), strength training will see greater increases in strength, and power. When strength and endurance are combined, most research shows that you will see similar results with increases in VO2 max, but the strength components will be inhibited by the endurance training (2, 4). There is an assumption that endurance training and upper body strength training can be done together and result in minimal interference effect, but there is not much research to support this idea.

Something to account for when prescribing exercises is fatigue of the athlete. Fatigue is expected to be greater with concurrent training, and it is part of the reason why most people think strength gains are inhibited during this type of training. The acute hypothesis states it is due to fatigue that concurrent training results in decreased strength gains when compared to strength training alone. An article over concurrent training states, “The acute hypothesis contends that residual fatigue from the endurance component of concurrent training compromises the ability to develop tension during the strength element of concurrent training. The degree of tension developed by the muscle during training is a critical factor in producing optimal strength development. If sufficient tension cannot be generated during the strength component of concurrent training, optimal strength development and adaptation may not occur (2).” Most of the research on concurrent training has the endurance training preceding the strength training, so what if we changed the order? The same concurrent training article finds that even with the reversed order, aerobic fitness is likely to be impaired (2). This finding seems to infer that any preceding bouts of strength or endurance training results in residual fatigue that inhibits the adaptation of the subsequent training activity.

Approach to Interference Phenomenon

TrainingScheduleHow do we minimize or maximize this interference effect? Most models of training for athletes will have an inverse relationship between intensity and volume, so let’s take a look at different training schedules and their adaptations. One article proposes different models to minimize and maximize the interference effect. The first example is a training schedule with high intensity interval training to improve aerobic power and an 8 to 12RM multiple set resistance training protocol to increase strength is a way to maximize the interference effect. The article goes on to say, “this effect occurs because the strength training will attempt to enhance the protein synthesis in the muscle, and stress the anaerobic energy system with corresponding increases in muscle lactate. At the same time the aerobic interval training will create hypoxia in the muscle, requiring the muscle to increase its oxidative capability (1).” These are a conflict of adaptations which will more than likely bring about the reduction of one of the systems. Another possible training schedule would be combining aerobic interval training with high intensity (3 to 6RM) resistance training. This type of training would bring about less interference because the training stimulus for increases in strength would stress the neural system and not place metabolic demands on the muscle. With this type of training we would assume that the muscle could increase its oxidative capability without affecting neural adaptation such as increased firing frequency, more efficient synchronization of motor units, decreased inhibition and co-contraction of antagonist muscles (1). The last proposed training schedule would be a continuous aerobic training with a high or medium load strength training protocol that would result in minimal interference. The same article states, “physiological adaptations associated with continuous training would be centrally mediated, involving increased cardiac output, haemoglobin and greater pulmonary diffusion. This type of training should not interfere with either neural adaptation or muscle hypertrophy since the location of physiological adaptation and metabolic response would seem to be different (1).”

The best way to look at this interference effect is to check it with your desired sport. Is your sport one that requires you to combine endurance and strength or does your sport require one of the two training methods? If your sport requires a combination of the two, then there is no escaping it. You will need to train both endurance and strength to properly compete in your sport, especially at the highest level. This is where the challenge of prescribing exercises comes in. Every coach has to know the requirements of their athlete’s sport and find a balance of the two methods to help their athletes succeed.  The proper balance of training, greatest end goal, and proper progression through the athlete’s season could mean the difference between a first and second place.

References:

  1. Docherty, D., & Sporer, B. (2000). A Proposed Model for Examining the Interference Phenomenon between Concurrent Aerobic and Strength Training. Sports Medicine30(6), 385-394.
  2. Leveritt, M., Abernethy, P. J., Bary, B. K., and Logan, P. A. (1999). Concurrent strength and endurance training. Sports Med., 28: 413-427
  3. Nelson A, Arnall D, Loy S, et al. Consequences of combining strength and endurance training regimens. Phys Ther 1990; 70 (5): 287-94
  4. Dudley G, Djamil R. Incompatibility of endurance and strength training modes of exercise. J Appl Physiol 1985; 59 (4): 1446-51
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