Interested in learning about the scientific aspects of eccentric training? In this blog, one of our users who is a PhD in Sport Science, introduces the basics of flywheel training science and the benefits of flywheel training devices compared to traditional weight devices. Read all about it below:
Types Of Muscle Contraction or Muscle Action
a) During a concentric contraction, the muscle shortens (reduces its length) and produces a force that is greater than the external resistance. Therefore, the mechanical work is positive (Work =Force x Distance).
b) During an isometric muscle action, the joint angle and the length of the active muscle do not change. In this situation, the mechanical work is zero because there is no displacement.
c) Finally, during an eccentric contraction, the muscle is lengthening due to external resistance. In this situation, the external resistance is greater than the force the muscle can produce and because the direction of the force is opposite to the direction of movement the mechanical work is negative. Practically in the gym when a participant lifts the barbell the agonist muscles act concentrically whereas when the participant lowers the barbell the muscles act eccentrically.
BENEFITS OF ECCENTRIC MUSCLE CONTRACTION or MUSCLE ACTION
Eccentric muscle actions provide a protective effect to the human body. In daily activities, e.g. when we are descending the stairs or when we lose our balance and place the other leg to avoid a fall, the muscle acts like a spring to absorb high-impact forces, to decelerate the body and support it against gravity.
In sports, such examples of absorbing high-impact forces which can cause injuries, are the landings from various jumps (vertical or even horizontal). These high-impact forces could reach 10-15 times the athlete’s body weight.
Another important benefit is that if an eccentric muscle action is performed immediately before a concentric muscle action, then elastic energy is stored, and the concentric action is potentiated. For example, a vertical jump from a squat position, which uses only the concentric muscle action is 10-20% lower than a countermovement jump which uses the combination of eccentric and concentric muscle action (the athlete first bends the knees and then immediately extends them).
This is called the “stretch–shortening cycle”. During the eccentric muscle action of a stretch–shortening cycle exercise, elastic recoil energy is stored. This elastic energy is returned to potentiate the subsequent concentric muscle action. Thus, the jump is greater than the concentric-only squat jump.
Eccentric strength has also been associated with maximum running speed, agility times, vertical jump height, and running economy. This means that the greater the eccentric strength the faster the sprint or the change of direction, the greater the jump, and the more economical the endurance runner.
ECCENTRIC FORCE PRODUCTION – LIMITATIONS TO ENHANCE ECCENTRIC STRENGTH DURING THE TRADITIONAL RESISTANCE TRAINING
The main characteristic of the eccentric muscle action is that 20-60% higher maximum force is generated compared to a concentric muscle action.
This means that the eccentric muscle action is under-loaded during traditional resistance training and is activated to a lesser degree because of the differentiation of maximum force between the two different types of muscle action.
For example, let’s assume that an athlete could lift 100kg for 1 repetition. This is his maximum concentric strength. If this athlete would like to train with a load of 75% of maximum, during the first repetitions his activation level will be 75% of maximum. Thus, he will activate 75% of his agonist muscles.
Let’s assume again that his maximum eccentric strength is 150 kg, and that the load that he uses is 75 kg. This means that for the maximum eccentric strength he trains at 50% of max. Thereafter he would activate the eccentric phase of the movement by 50% which is 25% lower than the concentric portion of the lift. That is why the eccentric muscle action is under-loaded during the traditional resistance exercise.
Eccentric training using a flywheel
Resistance training using a flywheel is known from the 18th Century (read more about flywheel training history). This method has also been used by NASA (US National Aeronautics and Space Administration) in the 1990s to prevent muscle atrophy in astronauts during space flights.
When performing an exercise with a flywheel device, the resistance is due to the flywheel moment of inertia as a result of its rotation and not due to gravity (there is zero gravity in space). Thus, the flywheel device is gravity-independent. During the concentric muscle action, when the participant gets up from a squat position by extending the knees, the rotation of the flywheel stores kinetic energy in the system.
Then, during the eccentric muscle action, when the participant is flexing the knees again, tries to absorb and neutralize the pre-produced kinetic energy. In this phase, the participant uses eccentric muscle action as a brake to decelerate the downward movement.
ADVANTAGES OF Flywheel TRAINING
Resistance training using the flywheel device has many advantages compared to traditional resistance training. The flywheel device is portable. The participant could carry the flywheel device anywhere he/she prefers (courts, fields, parks, etc.) to perform complete resistance training making this method time effective.
It also provides safety to the practitioner. People with special needs such as older persons, people under neuromuscular rehabilitation, or beginners in resistance exercise, could improve their strength using a controlled and easily adjustable load.
Furthermore, during traditional resistance training, execution technique is important because of the long moment arms, especially at smaller joint angles (e.g. knee angle at deep squats). This limitation is not observed when training with the flywheel device as it uses special equipment such as the harness which decreases the moment arms during squats.
Also, people could achieve all the goals of strength training using only one device. The participants may improve maximum strength, power, and muscular endurance and also achieve muscle hypertrophy. Research has shown at least equal, and in many cases better results compared to traditional resistance training.
Another advantage of the flywheel device is that the participants can perform general exercises (squats, deadlifts, etc.) as well as specific exercises for different sports in multiple planes and axes. The flywheel device provides accommodated resistance throughout the full range of motion according to the muscle length–force relationship.
It is known that the muscles produce different forces depending on the joint angle (i.e. at different muscle lengths). This means that force production is optimized for all joint angles throughout the range of motion of the exercise.
A “sticking point” or “sticking region” is not observed in the flywheel device. The “sticking region” is a portion in the beginning of the range of motion during the traditional resistance training which is the weakest region for the participant to lift the load because of the result of mechanical disadvantage (long moment arms).
When moving in the “sticking region”, movement velocity and force decrease and may be lower than the load of the barbell. Thus, the participant may fail to lift the load. In contrast, during resistance training with a flywheel device, movement velocity increases (accommodated resistance) until the end, and the lift is not limited by a sticking region.
When using a flywheel device, exercise intensity can always be maximum in every repetition. Furthermore, the magnitude of resistance may be adjusted to the level of fatigue, which is not possible with traditional resistance training.
For example, let’s assume that a participant performs repetitions with a barbell loaded with 50 kg. Failure is reached when he cannot apply a force at least equal to 50 kg, in which case they may be in danger and need assistance.
In contrast when training with a flywheel device the participant will continue performing repetitions until complete fatigue is reached. This is because the system is energy-based and not gravity-based.
If the exercise is the squat, the practitioner will apply lower and lower force to the flywheel, continuing to perform repetitions, since he will store in the flywheel less and less kinetic energy in each repetition due to fatigue, until he reaches the point of applying the necessary force just enough to lift his weight.
Finally, the flywheel device can generate an eccentric overload. This means that the force and power production of the eccentric muscle action is greater compared to the concentric muscle action and as a result activates the eccentric muscle action to a greater degree than the traditional resistance exercise.
PhD in Sport Science