There are a few reasons why an athlete may experience asymmetrical lean mass. The first and most obvious reason is laterality. Laterality is another way of saying handedness or footedness, which is the preference that most people have to perform physical tasks with one side of their body. For the average right-handed person, the right side of their body tends to be both stronger and larger, and the opposite for left-handed people.

It’s also not uncommon for people to have limbs of different lengths. For example, someone could have one femur (the large bone of the upper leg) that was longer than the other. Also, if one foot were larger than the other, it may turn out and flatten more, and could effectively make that same leg shorter. Like laterality, differently sized limbs can create preferences and imbalances that lead to a muscle being larger than its counterpart on the other side of your body.

In the study, researchers measured the muscle masses in various parts of the leg and pelvis of 167 Division I athletes. They then came up with a percentage of asymmetry to compare to the force and power profiles of the same athletes when they jumped. The researchers used what’s called a force plate, which measures the energy an athlete puts into the floor during a jump. Finally, they also measured the jumping height of each athlete.

The researchers learned that asymmetry of muscle development correlated to asymmetry in force and power. Asymmetries of the thigh and shank (the part of your leg between knee and ankle) could explain about twenty percent of force asymmetries. Similarly, imbalance in the pelvis, thigh, and shank together explained 25% of power asymmetry. As a result of muscle assymetry, jump height was reduced by a power asymmetry of ten percent or greater – an average of about 3.5 inches.

You might think these results don’t apply to you, but they certainly may. About five percent of the studied athletes fell into a range of power asymmetry that affected performance, so it wasn’t uncommon. Muscular asymmetry might also be masked by athletic ability. One of the best jumpers in the study had a power asymmetry of fifteen percent. Although he was one of the best, the imbalance may prevent that athlete from becoming even better.

Ensuring that power levels are similar on each side of your body is important for maximum performance in athletics. Maintaining strength on both sides goes a long way in staying healthy and strong.

References:

1. David Bell, et. al., “Lean Mass Asymmetry Influences Force and Power Asymmetry During Jumping in Collegiate Athletes,” Journal of Strength and Conditioning Research, 28(4), 2014

Photo courtesy of the Journal of Strength and Conditioning Research.

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The mixed results are a product of the huge number of potential variables at play with this protocol. A research team tried to nail down some of these variables in a recent Journal of Strength and Conditioning Research study.

Whenever you perform an exercise, both the agonists (the muscles moving the weight) and the antagonists (the muscles that oppose the agonists) are activated. The stretch reflex, responsible for the knee jerk reaction at the doctor’s office, is likely a primary reason for the activation of the antagonists. This reaction supports stability of the joints by preventing hyperextension or hyperflexion. Without it, you would constantly be injuring yourself.

However, despite its protective benefits, the stretch reflex yields smaller net forces during exercise. This is the basis of the antagonist paired sets method. If an antagonist muscle group is fatigued prior to performing an exercise, they will be less able to create a strong stretch reflex. This method should be used only as an advanced technique in experienced lifters, since you are actively reducing joint stability when you use it.

In the Journal study, the researchers chose to focus on rest intervals as the key variable. The participants were tested for their ten-rep maxes in both knee extension and knee flexion. Each person tried knee extension all by itself and also after a bout of knee flexion. They used four rest intervals between the knee flexion and extension:

• Thirty seconds
• One minute
• Three minutes
• Five minutes

Not only did the researchers measure performance, but this was also the first study of its kind to record EMG activity, which measures the degree of activation of the muscles. It’s possible that even if performance dropped, the muscles might be activated to a greater extent.

The researchers found that antagonist pairing improved performance when the antagonist exercise was performed immediately before, thirty seconds before, and one minute before the agonist set, but not longer. They also noted some increased EMG activity with up to thirty seconds as well. To give you an idea of the significance of this, when the knee flexion was done immediately prior to the knee extension, the ten-rep max could be performed for thirteen reps, which was a thirty percent improvement in repetitions.

So antagonist pairing does work, at least on single-set efforts. Since the much-written-about post-activation potentiation (PAP) has also been shown effective, but after a longer rest period, I’d love to see a study that pairs PAP and antagonist pairing to see if further benefits result. Imagine if every set could be fifty percent better. Science is a wonderful thing.

References:

1. Marianna de Freitas Maia, et. al., “Effects of Different Rest Intervals Between Antagonist Paired Sets on Repetition Perfomance and Muscle Activation,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000451

Photo courtesy of Shutterstock.

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