Physiological adaptations to high intensity short duration training types
High intensity strength, power, speed and hypertrophy training tend to cause the greatest adaptations in the neuromuscular system because they require the greatest integration and coordination of musculature to perform specific tasks under high loads or in an explosive fashion. Some of the major adaptations are detailed in the following table.
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Physiological adaptations to high intensity short duration training types
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Fibre size
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- Muscle size increases with hypertrophy training and to a lesser degree strength training. This is due to an increase in the number and thickness of actin and myosin filaments, an increase in myofibrils and an increase in sarcoplasm (fluid within the muscle cell).
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Fast – twitch fibre behaviour
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- Strength, hypertrophy, power and speed training modalities all focus on contractions from fast twitch fibres, thus these training types improve the specific fast twitch function being trained, whether that is strength, speed, power, size or a combination.
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Nerve–muscle connections
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- Increased recruitment of additional motor units, which respond in a simultaneous fashion to improve force production.
- There is an increased activation of synergistic muscles to assist force production for strength, power, speed and hypertrophy.
- Neural pathways linking to target muscles become more efficient at transmitting the message (stimulus).
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Timing of neural stimulus
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- The timing of contractions becomes more co-ordinated, especially with power, speed and strength training, in order to meet the force generation required to move loads.
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Summation of motor units
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- The ability to summate (fire a lot of impulses in target muscles all at once) is improved with strength and power training because they require maximum activation of target muscles to create maximum force.
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Neuromuscular fatigue
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- Effective integration of multiple body segments to create explosive movements or lift heavy loads requires more neuromuscular involvement than any other training; hence strength, power, speed and hypertrophy training are the best types of training to improve the neuromuscular systems resistance to fatigue.
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Physiological adaptation to longer duration training types
The muscular system also adapts to training types that rely on the aerobic energy system as well as the anaerobic systems, such as muscular endurance and aerobic and anaerobic fitness. Some of these major adaptations from these types of training include;
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Physiological adaptation to longer duration training types
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Capillarisation
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- The number of capillaries in the muscle increase. This enables more O2 to be delivered to working muscles and more CO2 to be absorbed back into the blood thus improving endurance performance.
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Substrate storage
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- Muscles and liver increase their ability to store carbohydrate and fat so it can be used for ATP production more readily.
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Slow–twitch fibre behaviour
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- As the duration of training lengthens slow twitch (endurance) fibres become increasingly dominant. Aerobic fitness, anaerobic fitness and muscular endurance training all improve the function of slow twitch fibres.
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Mitochondria
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- Mitochondria as you may remember from the energy system section are the aerobic powerhouse of the muscle cell. The number of mitochondria increases with aerobic exercise enabling more aerobic metabolism to take place. This means the muscle can create more ATP aerobically and results in less lactate being produced during workouts below anaerobic/lactate threshold.
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Motor unit firing adaptations
With the exception of flexibility training, all the other training types improve the effectiveness and efficiency of motor unit firing. They do this through what is known as ‘motor learning’.
As motor units send the stimulus from nerve to muscle, then quite simply the more they do this the better they get at it, messages don’t get sent to the wrong muscles en route and messages also get to their target muscles with increasing speed and less delay.
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