The Magic of Muscle Adaptation

CEU Article Title: The Differences between Anaerobic and Aerobic Adaptations in Training

By: The NCCPT Education Staff

Have you ever wondered about how the body performs and adapts under varying conditions? If you are training athletes of any caliber, this is a must read!

Aerobic training consists of submaximal efforts or training over extended periods of time. Aerobic adaptations to training include increased oxygen utilization and cardiac output and may often increase anaerobic threshold, VO2 max and decrease body fat.

As one trains aerobically, respiratory adaptations occur as breathing frequency is reduced and tidal volume is increased in submaximal exercise. While with maximal exercise, both tidal volume and breathing frequency increases (Baechle & Earle,2008, p. 129). The increased myoglobin that results from aerobic training transports more oxygen, and this allows the cells to produce more ATP aerobically. Neural adaptations occur as motor patterns become more efficient as fatigue of the contractile mechanisms are delayed. The Law of Facilitation states, “When an impulse has passed once through a certain set of neurons to the exclusion of others, it will tend to take the same course on a future occasion and each time it traverses this path the resistance will be less.” The body learns how to burn fat more efficiently and can eventually remain aerobic at higher intensities. “Improved aerobic performance may result in a rotation of neural activity among synergists and among motor units within a muscle” (Baechle & Earle, 2008, p. 129).
Muscle adaptations contribute to the body’s ability to perform longer at a higher intensity as well. Type I fibers can utilize fat for fuel as long as there is enough oxygen present.

Presto Chango?

Type IIx fibers may eventually convert to Type IIa fibers. Type IIa fibers have a greater oxidative capacity than Type IIx fibers. These can take on characteristics of a Type I fiber and become more efficient at endurance exercise which in turn helps spare glycogen and extend performance (Baechle & Earle, 2008, p. 129).
The muscle fiber’s adaptation to aerobic training produces changes in hormone production, which reduces the production of lactic acid and increases the rate of lactic acid removal. The greater the utilization of oxygen, the less lactic acid is produced. At the cellular level, the size and the number of mitochondria increase, and this increases the ability for the muscle to aerobically produce ATP (Baechle & Earle, 2008, p. 129). This adaptation, along with the additional increase in myoglobin mentioned above, helps the muscle tissue to grab and utilize oxygen. These adaptations also increase enzyme activity involved in glucose metabolism and fat utilization.

Wolff’s Law

Bones can also adapt to aerobic activity as they respond to the magnitude of the load. Wolff ’s Law states that if loading on a particular bone increases, then the bone will remodel itself over time to become stronger to resist that sort of loading. Therefore, any stress or exercise, including aerobic exercise, may stimulate bone formation. With anaerobic exercise or training, neural adaptations occur as a person intends to maximize strength, speed and power. The neural increases are thought to occur via the prime movers; their firing rate and the sequence of firing in muscle recruitment along with the reduction of inhibitory mechanisms such as the Golgi tendon organ.

“The ability to increase firing rate appears to be essential to anaerobic training for maximal force and
power development”

(Baechle & Earle, 2008, p. 98).

Muscle fibers are recruited from lowest to highest as described in the size principle or recruitment. Higher
threshold motor units are recruited after all the motor units below it are recruited sequentially (Baechle &
Earle, 2008, p. 97). Preferential recruitment occurs as a result of anaerobic training; such as rapid changes of direction in force production and ballistic contractions seen in plyometric, speed, power and agility training, because there isn’t enough time to recruit all of the motor units in order.

Muscles adapt by increasing in size, also known as hypertrophy, and by changing their architectural components. In resistance training, pennate muscles increase the angle of pennation (Baechle & Earle, 2008,
p. 97). Hypertrophy occurs in all muscle fiber types, both slow and fast-twitch. Although mitochondrial density is less when training with heavy resistance, anaerobic training increases the mechanical stress on bone, tendons, ligaments, cartilage and fascia. In response, the bone, tendons, ligaments, cartilage and fascia must all increase their functional capabilities to provide extra support for the stronger, hypertrophied muscles. Anaerobic exercise, especially resistance exercise, may lead to elevated testosterone, growth hormone and cortisol for up to 15-30 minutes post-exercise in men (Baechle & Earle, 2008, p. 108).

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