NSCA CPT Chapter 5 – Resistance Training Adaptations

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Chapter Objectives

• Know the acute and chronic adaptations the body has to resistance exercise.
• Find the factors affecting the magnitude or rate of adaptations to resistance training.
• Make resistance training programs that maximize specific adaptations of interest.
• Make resistance training programs that avoid overtraining.
• Know the effects of detraining and how we can reduce them.

Basic Adaptations to Resistance Training

Acute responses are mostly referred to as responses to exercise. These occur in the body shortly after a bout of exercise.

Chronic adaptations are the changes that happen in the body after repeated bouts of training and stay around long after a training session is over.

Acute Adaptations

Neuromuscular Changes

Like all training, resistance training requires the activation of skeletal muscles.

Motor unit recruitment and rate factor coding are two factors that control muscle force.

Motor unit recruitment refers to the process of tasks requiring more force will recruit more motor units.

Rate coding is the control of motor unit firing rates.

The faster the firing rate, the more force will be produced.

Motor unite recruitment is based on the size principle. The size principle essentially says that the first motor units to be recruited are the smaller type I units, and then so on. 

Typically, motor units innervating slow-twitch motor units will have fewer fibers than those innervating fast-twitch fibers.

Muscular changes

Muscles experience fatigue throughout a set of resistance exercises. 

The factors of muscular change are tied to the two metabolic pathways that are mainly stressed during resistance exercise. And these are the phosphagen system and glycolysis.

We are unlikely to deplete all of our glycogen during resistance exercise, but we will likely use all of our creatine phosphates as its users first. 80% of ATP production happens from glycolysis during bodybuilding training.

Adequate carbs following training are needed to restore the lost glycogen.

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Endocrine Changes

Hormones are blood-borne molecules produced within the endocrine glands. 

The main hormone types are protein, peptide, and steroid hormones. 

Steroid hormones are derived from cholesterol, including testosterone and estrogen hormones.

Protein and peptide hormones are things like insulin and growth hormone.

Hormonal changes occur with acute bouts of exercise.

Large muscle mass exercise has a much greater stimulus than the smaller muscle groups. Higher volumes and shorter rest periods also produce greater endocrine responses from these hormones.

Chronic Adaptation

Neurological changes

Strength increases rapidly occur in the very early stages of beginning a resistance program. These changes are larger than can be accounted for by the changes in muscle size. We call these initial changes “neural factors”.

These improvements occur due to the improvements being made in skill in the performance of resistance exercises, especially with people who use free weights and need balance and efficiency of movements so they can be done well.

Many starters can’t activate all of their motor units, but with consistent training, they can start to activate them more, thus becoming stronger in that sense.

Cocontraction is the simultaneous activation of an agonist and antagonist during motor tasks.

Less cocontraction would mean fewer torque resisting movements. Following isometric resistance, we see decreases in this contraction.

Muscle Tissue Changes

Adaptation occurs in the muscles, ligaments, and tendons of the body. Hypertrophy is one of the more obvious chronic changes. Hypertrophy is defined as an increase in muscle size. This muscle size increase involves changes in volume and cross-sectional area.

Type II fibers have greater hypertrophy than type I muscle fibers.

Hyperplasia is the decrease in the number of muscle fibers. This hasn’t been shown to happen in humans, but it does in animal models.

Force and power production both increase when hypertrophy occurs.

We can also shift our fibers from one type to another. Mostly this occurs from the IIa and IIx fibers.

Skeletal Changes

Bone serves as a depot for important minerals for the body and it serves as the connection point for the muscles in the body. 

Osteoporosis is the consequence of a long term net demineralization of the bone. Resistance training has positive long term effects on bone mineral density due to the stress and the body needing to overcome it. Women are typically at a higher risk for osteoporosis, so it is of more benefit for them to partake in some form of resistance training for that prevention.

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The greater the bone mass is before going through menopause, the less severe the consequences will be of bone loss later in life. 

Tendon and Ligament Changes

Ike bone and muscle, the tendons, and ligaments change due to added stress from training over time. They increase in strength in many similar ways. 

Both of these connective tissues are made up of fibrous collagen bundles. These don’t require much blood, oxygen, or nutrients, which makes them take longer to heal.

Like with bone, we strengthen these by adding load and consistently training them.

Things that change are things like tenon stiffness but not the actual thickness of the tendons.

Metabolic Changes

Hypertrophy dilutes enzyme and substrate levels, meaning that absolute level changes result in no relative changes. Relative decreases in concentration may mean you have hypertrophy occurring.

Some studies show ATP and Creatine Phosphate increases, but others are more inconclusive.

Resistance training involves the most changes to the anaerobic metabolism due to those systems being trained the most.

Endocrine Changes

Long term hormonal changes are less clear than the other changes.

Chronic resistance training sees more increases in the acute rises in growth hormone from training. This likely has something to do with long term muscle hypertrophy.

Chronic resistance training may affect the magnitude of the other endocrine responses and even the sensitivity of the tissues to certain hormones.

Cardiorespiratory Changes

Increasing Cardiorespiratory endurance capabilities need aerobic endurance specific training to achieve the best results. But, resistance training may augment cardiovascular endurance performance and efficiency in running by increasing the strength and power of muscles.

Body Composition Changes

Because of changes that occur in the muscles and hypertrophy, for example, we see more fat-free mass added to the body, and therefore body composition changes with that addition. We also see reductions in fat mass in the body. So with that two changes, you can see the changes occurring in BMI, for example, would bode well for showing positive body comp changes. 

The Fat-Free Mass increase also leads to a higher resting metabolic rate and total daily expenditure.

Factors That Influence Adaptations to Resistance Training

Specificity

Training is highly specific. So, the body adapts to exercise to perform optimally in the type of exercise stressors being put on it. So, running a mile would not help someone’s bench press. 

This matters the most when we are looking at sports training. If you are training for a sport, you should train with movements and skills that apply to how you move in them.

Sex

Both genders respond to resistance training similarly, but males and females show big quantitative differences in strength, muscle mass, and hormone levels.

When looking at strength, the large difference between males and females comes mostly from the difference in body size and body composition. Men tend to be larger and their added muscle mass increases strength further. Women usually have a higher body fat percentage than men, so less muscle per pound of weight affects performance. Adult males have 10 times more testosterone in their bodies than women of the same age. Other sex-related differences come from proportions. Men are larger in their upper bodies, and women are more so in their lower bodies.

When seeing the difference in strength per pound based on fat-free mass, the differences shrink. So it is indistinguishable if you are strictly looking at muscle cells.

Age

Aging produces many changes in the body. Sarcopenia begins in the 30s and this is the time when muscle mass decreases progressively over time. The quality of muscle also decreases along with this quantity decrease.

The ability to produce force goes down, and so does the ability to produce force rapidly. This is partially from the affected unit recruitment.

Aging muscular effects can be moderated or even reversed somewhat with continuous and high-intensity exercise.

Genetics

Human beings are unable to pick the activities they will be successful in. It is more or less determined by the genetics that you are born with. Everyone has what is known as genetic potential. We have set percentages of Type I and Type II fibers, and it is impossible to change them too significantly. The average untrained client, however, will always see more improvements in his or her genetic potential than some athletes who is well trained over time. 

Overtraining

Physical adaptation may be best brought on through training volume and intensity increases, but at some point, more is not always better. When we have inappropriate levels of volume or intensity, this will lead to something known as overtraining. 

This condition essentially occurs when someone is training too much. It can result in general fatigue and injuries.

We see a big decrease occurring in performance. 

The symptoms we see from overtraining are:

• Plateau followed by decreases in strength gains
• Sleep disturbances
• Decreases occurring in lean body mass
• Lessened appetite
• Colds that won’t go away
• Persistent flu symptoms
• Loss of interest in training
• Changes in someone’s mood
• Muscle soreness that seems excessive.

Detraining 

These physiological and performance adaptations happen when someone stops or at least significantly reduces their exercise.

These changes are the opposite of what happens in a training program. 

You essentially regress to the person you were before starting. But this process typically takes twice as long to lose your gains as it did to get them. 

Short term detraining, which is about 14 days, has been shown to have little effect on muscle strength and explosive power for more experienced athletes.

Extended detraining of 32 weeks will result in significant decreases in our muscle strength but still, remain higher than before starting.

You can delay and significantly reduce the effects of detraining by training only once or twice weekly.

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