Adaptations to Anaerobic Training

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Anaerobic training, by definition, consists of any exercise training that is done at a high-intensity such that oxygen is not needed. However, many anaerobic training programs use some degree of aerobic metabolism (with oxygen); therefore they are often concurrently trained. These bouts of anaerobic exercise happen intermittently, with varying rest periods in between. They include weight training, plyometrics, speed and agility drills, as well as interval training. Depending on the metabolic demands of each type of training, different adaptations will occur in the body such as muscular strength, power, hypertrophy (muscle growth), and muscular endurance. However, anaerobic training as a whole will result in critical physiological adaptations to the nervous, muscular, connective tissue, endocrine, and cardiovascular systems which we will further discuss.

Nervous System
The nervous system is the network of nerve cells and fibers that transmit nerve impulses between different parts of the body. 

When training, neural adaptations typically occur before structural changes in skeletal muscle occur. 

Knowing this, it is important for strength and conditioning specialists to stress that any structural improvements (i.e. hypertrophy) will only happen after neural adaptations have already taken place.

Anaerobic training is often done to help facilitate maximal recruitment of motor units, especially fast-twitch units (type 2 fibers). A motor unit consists of a motor neuron and all the muscle fibers it innervates. In untrained individuals, this recruitment of motor units is limited.  Even in trained athletes, motor units are recruited from smallest to largest, known as the size principle. Once recruited, the firing rate of the muscle is then taken in to account. Motor units that fire quickly are used primarily for high force, speed or power production. A combination of a large recruitment of motor units that also fire quickly results in maximal power output. There is evidence to support the notion that anaerobic training can enhance firing rates of recruited motor units.

Muscular System
The main adaptations to anaerobic training on the muscular system are increased muscle size (hypertrophy), fiber type transitions, and changes in chemical components. These changes can result in enhanced muscular strength, power, and endurance. 

Hypertrophy changes due to anaerobic training depend on the training status of the individual. It may take at least a few weeks before muscle hypertrophy becomes evident. However, similar to power and strength improvements, the initial hypertrophy gains that are observed are the greatest. Additionally, individuals who genetically possess a large proportion of fast-twitch muscle fibers may have greater potential to increase muscle mass than those with predominantly slow-twitch fibers. Muscle fibers generally don’t change from a type I to a type II (or vice-versa), however changes within a subcategory (changing from type IIa to IIx) have been observed.

Connective Tissue
Bones, ligaments, tendons, fascia, and cartilage are all examples of connective tissue in the human body. Any increase in muscle strength of hypertrophy will subsequently increase the force exerted on the connective tissue. As such, connective tissue (especially bones) must increase in mass and strength to provide sufficient support.

In order for bone growth or formation to occur, the force of anaerobic training must exceed the minimal essential strain (MES). Anything below this threshold, and bone formation will not occur. Exercises that do exceed the MES and that are most effective for bone formation is those that are weight bearing, although the specific load is dependent for each muscle group.

 This will also result in an increase in bone mineral density (BMD), which is the quantity of mineral deposited in a given area of bone. 

Conversely, inactivity will result in a rapid loss of BMD. Thus, it is important for strength and conditioning specialists to use exercises that stimulate muscle hypertrophy and strength, which will in turn stimulate bone growth as well as an increase in BMD.

Endocrine System
Hormones play an important regulatory role in adaptations to anaerobic training. Anabolic hormones are those that involve a building up process, whereas catabolic refers to the breaking down process. The main anabolic hormones that are involved in the development of muscle, bone, and connective tissues are testosterone, insulin, insulin-like growth factors (IGF), and growth hormone.

Anaerobic exercise (especially resistance exercise) has been shown to result in elevated testosterone, growth hormone and cortisol levels for up to 30 minutes post-exercise.  The magnitude of elevation for these hormones depends on the type of exercise as well as muscle groups that are worked. Exercises that use large muscle groups and that are moderate to high intensity with short rest intervals results in the highest elevations. These elevations due to an anaerobic workout may improve as training experience grows, as the individual is gradually able to exert more effort in training sessions. Therefore, it is important for strength and conditioning specialists to understand and implement the principle of progressive overload to account for an individual’s adaptations to resistance training. 

Cardiovascular System

Anaerobic resistance training can benefit the cardiovascular system in a different manner than which conventional aerobic training does. In acute bouts of anaerobic exercise, there is an increase in cardiac output, stroke volume, heart rate, oxygen uptake, systolic blood pressure, and blood flow to the active muscles. Stroke volume and cardiac output are increased mostly during the eccentric phase of each repetition, whereas heart rate and oxygen uptake are increased the most immediately following the exercise, especially when the Valsalva Maneuver is used. As an individual continues to train in anaerobic resistance training, the cardiovascular responses become less for each subsequent exercise session. Knowing this, it is important for strength and conditioning specialists to adhere to the principle of progressive overload, and continually tax the cardiovascular system in order to see further improvements. 

Kalan is a Human Performance Expert & PhD. Candidate who aims to optimize YOUR performance for both sport and every day life. He is recognized as a Certified Strength & Conditioning Specialist (CSCS) with the National Strength & Conditioning Association (NSCA), and has obtained his MSc. Kinesiology degree at the University of Victoria. Through his masters thesis research, Kalan has established and implemented the KFit Test Battery for Combat Sport Athletes which is used by both Karate BC & Karate Canada as their standard fitness test for  athletes across the country. Additionally, Kalan is an exercise physiology lab instructor at the University of Victoria, and trains individuals (including athletes) every day to help meet their fitness needs and goals. He has many years of experience both as an elite athlete and high performance coach and is knowledgeable in the many fields surrounding fitness and training for sports performance.