Benefits of Anaerobic Exercise

Today we will discuss the adaptations which result from anaerobic training. Anaerobic training occurs at a high intensity which cannot be satisfied by the aerobic energy system. Examples of anaerobic training are the 100-meter sprint, deadlifting for 5 reps of 80-90%, and even a javelin toss. To receive the benefits we will discuss training principles and factors that may impact adaptations. 

Neural Adaptations to Resistance Training

You may be surprised to learn that the first adaptation to training is neural. This means your nervous system typically adapts before your muscles hypertrophy or grow in size. An increase in neural adaptations occurs in the first 6-10 weeks and hypertrophy takes over as the primary adaptation after that.

• • Neural Drive & Central Adaptations
    • When you think about moving, signals descend from your primary motor cortex to activate muscles. Anaerobic training can adapt your spinal cord to activate fast twitch motor units to produce force faster. This adaptation happens by increasing the firing rates of neurons, motor learning and synchronization, and agonist muscle recruitment. In the untrained population, only 71% of muscle tissue is activated during maximal contraction. By learning to fire your nervous system efficiently this makes up the bulk of early training adaptations. Lifting increases the synchronicity of unit firing. This may be a large part of motor learning adaptations or the mind-muscle connection. 

• • Inhibition of the Golgi Tendon Organs (GTOs)
    • • Inside the tendons of your muscle, there are sensors called GTOs that relax the muscle when the tension is too high. This prevents the tendon from tearing. Imagine your bicep curling 225 pounds, your GTOs would hopefully inhibit this tension before a rupture. Progressive overload offers a pathway to relax this protective feature allows us to lift more weight with properly dosed progressive overload. This is a good thing because our tendons, cartilage, and muscles adapt to hold more load as we train. 

• Frequency and Summation
  • • Your nervous system works by sending and receiving electrical signals. With anaerobic exercise, there is an increased frequency of electrical signals. This causes muscle twitches to overlap causing increased strength. Heavy strength training stimulates the firing rate and recruitment of neurons yielding improved force production. 

• Size Principle
  • Motor units are recruited in order of size from smallest to largest. Walking or sitting recruits smaller type-1 slow twitch muscles. When you run a marathon you use your type 1 soleus muscle to produce low forces for a long time. Sprinting or deadlifting will require the recruitment of larger fast-twitch type-II motor units. As you exercise you use the motor units you train which can adapt. Selective recruitment is skipping low threshold units to fire larger threshold units. This may occur when force production is required at high speed. Skipping to larger units may be selectively trained owing to the principle of specificity.
  • All muscle fibers will hypertrophy because motor units are recruited in order of size. Advanced lifters can activate motor units nonconsecutively by skipping smaller units. As muscle size increases, less neural activation is needed to lift the same load.
• Neuromuscular Junction (NMJ)
  • The neuromuscular junction is the space between the nerve and skeletal muscle fibers. It is how the nerve communicates with muscles. The NMJ can increase in total area in both high and low-intensity training. Greater end plate perimeter length and area as well as greater dispersion of acetylcholine receptors in the end plate were found after 7 weeks of training.
• Myotatic reflex
  • Contraction of a muscle in response to passive stretching also known as the knee-jerk reflex. Harness the involuntary elastic properties of muscle and CT and acts to increase force production without additional energy. Resistance training increases potentiation by 19 to 55% in bodybuilders and weightlifters.
• Electromyography (EMG)
  • Surface pads can monitor the magnitude of neural activation in muscles. Intramuscular needles can more accurately measure electrical conduction. Training reduces antagonistic muscle activation, allowing agonists to perform the desired action with less resistance. A plateau may occur because of accommodation to the training load. The principle of progressive overload will allow continual neural adaptation. Neural factors are important for strength gains in programs with higher than 85% 1rm.

• Cross-Education
  • Exercising muscle asymmetrically produces strength and neural activity in both muscles. This suggests that a central neural adaptation accounts for a significant amount of strength adaptation.

• Bilateral deficit
  • The force produced when both limbs contract together is lower than the sum of forces contracting unilaterally. However, bilateral facilitation can be trained. An increase in voluntary activation of the agonist muscle groups can occur.

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Muscular Adaptations to Resistance Training

• Hypertrophy
  • Hypertrophy is the increased cross-sectional area, CSA, with resistance training. This is the principle that bodybuilders use to maximize their size. Hypertrophy occurs when there is more production than destruction of actin and myosin in the muscle fiber. There is also an increase in the number of myofibrils within a muscle fiber, contributing to size.

• How Can We Control Muscle Hypertrophy?
  • The body is careful where it invests energy. It prefers to conserve precious resources for the brain and heart to use to keep us alive. In order to convince the body to spend resources on building muscle, a sufficient threshold must be reached. This is why moderate to high intensity is needed to stimulate change. We will need to intentionally expose our muscles to time under tension.
    • We will not speed through the repetition and will control the concentric and eccentric. 
    • We will use the full range of motion when safe to do so. This means we will not stop the exercise short and will use the available range to stretch and shorten the muscle.
    • We will progressively overload volume by no more than 10% a week. Beginners can start low with 1-2 sets of 10 repetitions and build to 3-4 sets of 8-12 reps per exercise. Listen to your body for signs of overtraining, pain, an excessive fatigue.
    • Start with body weight, light weights, or an empty bar, and ensure correct form. This is to ensure we can lock in the correct movement pattern with motor learning.
    • A relatively short rest period between 30 seconds to 60 seconds is preferred for bodybuilding. Longer rest periods of 1-5 minutes may be required for larger, heavier movements.
    • Mechanical deformation of tissues stimulates the machinery inside the cell to adapt to the stimulus. Signals increase when fibers contract, increasing muscle protein creation called myogenesis. Resistance training downregulates inhibitory growth factors like myostatin. The sum of these intracellular changes causes protein synthesis rates to remain elevated for up to 48 hours after stressed.
      • This growth is multifactorial, nutrition, stress stimulus, hydration, and hormones all contribute to growth. With heavy resistance training, fast myosin-heavy chains replace other muscle proteins within a few sessions. True hypertrophy requires a longer period of 16 workouts to see growth.

• • • Eccentric Training: the lowering or downward phase of a movement.
      • The inclusion of eccentric training allows for greater force production and adaptation. For Instance, I cannot perform many pull-ups, so implementing the downward portion for reps allows me to provide more stress with less volume.

• • • Metabolic factors:
      • Low to moderate intensity with high volumes and short rest intervals. Metabolic stress adapts the glycolytic energy system which may aid in muscle growth. This means higher volume 3-5 sets of 10 reps with 30-60 second rest will metabolically stress the tissue to stimulate adaptation.

• • • Hyperplasia:
      • The number of muscle fibers increases. Whether or not this occurs in humans has been debated, however, it has been shown to occur in animals. If it occurs at all, it is not the primary response.

• • • Fiber Size:
      • Not all motor units are composed of the same fiber type. Slow twitch type-1 fibers are smaller and are predominately for aerobic endurance like the soleus for marathon running. Fast twitch type-2 fibers hypertrophy more than slow twitch Type-1 fibers. Your genetic makeup largely determines what proportion of fibers you have. 

• • • Fiber type transition:
      • Type 2x fibers change to 2a fiber type to become more oxidative. High-intensity resistance training and aerobic endurance stimulate this change 2x→2a. Detraining causes the opposite, where type 2a fibers are replaced by type 2x.

• • • Pennation angle:
      • Refers to the feathered position muscle fibers attach to their tendon. Greater pennation causes more protein deposition and CSA which correlates with force production. Resistance training increases the angle of pennation

• • Metabolic Muscle Adaptations
    • Inside the body, there are many adaptations to improve our resilience to training. Inside the muscle, there is an increased myofibrillar volume, cytoplasmic density, SR and T-tubule density, sodium potassium ATPase activity, and calcium release which all support force production. Sprinting increases calcium release which increases speed and power by optimizing cross bridge formation. Bodybuilding produces metabolic stress with increased h+ concentrations which must be circulated and buffered.  Buffering potential can increase with HIIT training by upregulating protein enzymes.
    • Creatine phosphate and ATP concentrations are super compensated after being exhausted. A 28% increase in CP and an 18% increase in ATP occurred after 5 months of resistance training with 3 to 5 sets of 8-10 reps with 2-minute rest or less. Glycogen content can increase up to 112% with resistance training.

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Connective Tissue Adaptation

When we exercise, we exert forces on our bones, tendons, ligaments, fascia, and cartilage. Our body can sense this stress and can adapt in response to the stimulus.

• Bone
  • Wolff’s law states that when a bone is loaded it will adapt to become stronger to resist that stress. This law can be used to fight and prevent conditions like osteoporosis, and low BMD, with progressive bone-loading exercises. The rate a bone will adapt depends on the ratio of spongy trabecular bone to cortical compact bone. Trabecular adapts more quickly because of its greater area-to-mass ratio.  It is less dense and more flexible, owing to its sensitivity to adaptation.

• Minimal Essential Strain (MES)
  • MES describes the threshold needed to initiate new bone. Walking may not present enough strain on the bone to adapt. Squats or sprinting may meet the threshold to grow. As the bone becomes stronger, more stress is required to stimulate growth which is why we progressively load exercises.

• Bone Mineral Density (BMD)
  • Even if your goal is not to look like a bodybuilder this concept is important for you. As we age, if we are inactive our bone matrix dissolves as it is never stimulated to adapt. This may result in atrophy so severe that sitting in a chair too fast, sneezing, or falling can cause bones to easily fracture. Therefore, it is my belief that progressive resistance exercise should be implemented to age gracefully.

• Specificity
  • Running will increase BMD for the legs but not the arms. Tissues will only adapt when they are intentionally stimulated.

• How to grow bone
  • The time required for bone to significantly adapt is approximately 6+ months however, the process begins immediately. Bone growth-focused training needs loading, speed, direction of loading, volume, overload, and variation.
  • Multi-joint exercises with force vectors through the hip and spine are structural exercises.
  • Structural exercises are deadlifts, squats, cleans and jerks, and overhead presses because the load is transmitted through the spine and hip.
  • Use a variety of exercises so the bone faces novel stimuli to adapt. 
  • To stimulate the bone, machine-based exercises, and isolation exercises should be limited because they isolate single muscle groups without properly loading bone. Instead, use body weight and free weights such as push jerk, deadlift, and shoulder press.
  • Bone health is multifactorial, exercise and loading is only one piece of the puzzle. Your hormones, nutrition, hydration, sleep, and overall health all contribute to having quality bone density.

• Peak Bone Mass
  • We meet peak bone mass between 25 and 30 and begin slowly losing density after 40. With training, we can increase our peak and start from a higher peak when we decline. This will allow us to have comparatively more bone mass as we age.

• Tendons, Ligaments, and Fascia
  • Collagen fibers make up all connective tissue. Procollagen is made of 3 proteins twisted in a triple helix which is created by fibroblasts. Microfibrils are strands of collagen that are parallel. The proximity of the strands causes cross-linking which is how bonds form between adjacent collagen molecules. 

• • Tendons and Ligaments
    • Made of parallel collagen bundles, composed of very few metabolically active cells. Thus very little oxygen and nutrients are needed for them to survive.
    • Ligaments
      • Connect bone to bone, such as your ACL or anterior cruciate ligament connects your femur to your tibia.
      • Contain elastin and collagen to allow a stretch.
    • Tendons
      • Connects muscle to bone, such as your biceps tendon in your elbow.
      • Poor vascularity and circulation cause poor regeneration and healing if an injury happens.
    • Fascia
      • Fibrous connective tissue that surrounds and separates skeletal muscle. Bundles of collagen fibers are arranged in different planes that converge near the end of the muscle to help form a tendon.
    • Cartilage
      • Dense connective tissue provides smooth joint surfaces such as hyaline cartilage in your knee. Cartilage acts as a shock absorber as fibrous cartilage comprises some of the intervertebral discs in your spine. Cartilage lacks its own blood supply causing poor healing in the case of injury. Nutrients arrive from joint fluid from diffusion. Thus rhythmic joint motion helps cartilage to bathe itself in synovial joint fluid for healing. 
        • Immobilization of joint yields in poor diffusion of oxygen and nutrients causing death of healthy cells. The use it or lose it phenomenon is apparent here, with disuse, cartilage will thin.

• Connective Tissue Adaptations

• • • Stimulate growth with progressive loading from external resistance through the full range of motion.
      • Low intensity will not change collagen content, thus the intensity needs to be significant.
    • Adaptations occur between the tendon or ligament and their bone attachment, within the body of the tendon, and the fascia over the muscle.
    • As muscles become stronger they pull on bone with more force causing connective tissue to adapt. With training, tendons can Increase collagen fibril diameter, covalent bond cross-links, density of fibers, and number of collagen fibrils. As we stimulate muscle growth, connective tissue will adapt to withstand the increased force capacity. For example, a 15-19% increase in Achilles tendon force transmission was found after 8 weeks of resistance training.

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Endocrine

Hormones regulate many functions in the body, and anaerobic exercise provides a stimulus for many body systems to adapt.

• Acute Anabolic Hormone Response
  • After anaerobic exercise elevated testosterone, growth hormone, and cortisol have been found for up to 30 minutes in men.
  • A larger release of hormones will occur when greater muscle mass is recruited to perform compound movements with high intensity with short rest intervals.
  • Insulin-like growth factor 1 (IGF-1) 
    • Released with exercise to acts as a hormonal messenger that stimulates cells to adapt. Targets are skeletal muscle, cartilage, and bone. Hormones have a delayed response with exercise.

• Chronic Response to Acute Hormone Stimulation

• • • Long-term training can cause systemic changes in the body. For instance, resistance training can increase muscular force production. As exercise intensity is tolerated, the body adapts to become more resilient.

• Resting Hormone Adaptations
  • Resting hormones are unlikely to change chronically in testosterone, IGF-1, or cortisol levels. However, blood concentrations likely represent the current stresses imposed by nutrition, exercise intensity, and stress. If levels were chronically elevated, the receptors would downregulate with sustained exposure. This is the reason why anabolic steroid users cycle rather than maintain consistently high doses to maintain receptor sensitivity. 

• Hormone Receptor Changes
  • Receptors are essential for hormones to communicate a signal. Resistance training can upregulate receptors within 48-72 hours following training.
  • For example, 1 set versus 6 sets of 10 reps of squats.
    • Higher volume resulted in the downregulation of receptors
    • Consumption of protein-carbohydrate supplements before and after a workout attenuates the downregulation of receptors.

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Cardiovascular and Respiratory Adaptation to Anaerobic Training 

To sustain activity with increasing intensity, the heart and lungs must adapt. Heavy resistance training stimulates increased tolerance for high-pressure environments.

• Cardiovascular response to Anaerobic exercise.
  • With anaerobic training, heart rate, stroke volume, cardiac output, and blood pressure increase. For instance, an HR of 170 and blood pressure of 320/250 mmHg have been found with heavy leg pressing. Blood pressure increases nonlinearly with muscle mass recruited in the concentric phase. Stroke volume and cardiac output increase during the eccentric phase, particularly with the addition of the Valsalva.
  • After the completion of a set, the heart rate is higher than during the set itself. This is because the body must the oxygen debt from the intense work.
  • Blood flow is directed to the working muscle depending on the intensity, duration, and size of the muscle recruited. There can be 5-20 times increased cardiac output with exercise, with most blood being sent to active musculature.

• Reactive Hyperemia
  • • Muscle contractions greater than 20% of maximal voluntary contraction impede peripheral blood flow. The response is a rush of blood flow during rest. This is the theory seen in blood flow restriction training which has shown good results with hypertrophy. Lack of blood flow increases h+ ions and reduced pH which are potent stimuli for muscle growth.

• Cardiovascular Adaptations at Rest

• • Heart rate
    • Short-term resistance training reduces HR by 5-12% or none at all. Cardiovascular exercise is the best way to reduce resting heart rate.

• • Blood pressure
    • Both systolic and diastolic blood pressure decreased by 2-4% with resistance training with the largest effect seen with higher starting BP.
    • Rate-pressure product = HR X Systolic BP
      • A measure of how hard the heart is working has been shown to remain constant or decrease with resistance training.

• • Stroke Volume
    • • • Increases in proportion to lean muscle mass. This means that more blood is ejected every heartbeat.

• • Cardiac hypertrophy
    • The heart physically grows in thickness with resistance training. It may occur because of the increased pressure the left ventricle contracts against when exercising. Interventricular septum and posterior left ventricular wall thickness increase as well.

• • End Diastolic Volume
    • This is the amount of blood in the ventricular chamber before systole or ejection occurs. This increases in bodybuilders but not weightlifters and is thought to be more of an aerobic adaptation. This could be high-volume training of bodybuilders or it may be confounded by the supplementary cardio bodybuilders do to maintain desired body fat.

• Adaptations of the Cardiovascular Response to Anaerobics

• • Chronic resistance training blunts the increase in HR, BP, and rate pressure product with adaptation to workload. Bodybuilders have been found to have less blood pressure when training compared to sedentary populations. This may be due to slightly higher oxygen use with high volume and short rest periods. Alternatively, it may be due to a reduced afterload due to stronger ventricular ejections with each heartbeat.

• Ventilatory Response to Anaerobic Exercise

• • Ventilation is the air we breathe in order to get oxygen to our tissues. The ventilation rate increased while training but is elevated more during rest periods as we recover primarily aerobically. Shorter rest periods of 30-60 sec yield the most ventilation. Other adaptations include Increased tidal volume and breathing frequency. Interestingly, with submaximal effort, tidal volume remains elevated while frequency is lowered owing to true ventilatory adaptation with resistance training.
  • Ventilatory equivalent 
    • The ratio of air ventilated to oxygen consumed by tissues. This is reduced demonstrating an efficiency advantage in the trained.

• Aerobic and Anaerobic Training
  • Resistance training helps the performance of aerobic athletes. This is due to the increased strength, endurance, and power anaerobic training provides.
  • High-volume aerobics may decrease the strength and power of resistance athletes. This is only relevant for those who compete and In my experience, the benefits of cardiovascular health outweigh the decrement in power output.
  • Heavy resistance training recruits more type 2x fibers than aerobic endurance high-intensity interval.

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Anaerobic Adaptations

• Muscular Strength
  • Training may cause a 40% strength increase in the untrained. This is likely due to motor learning and secondarily hypertrophy. A 20% of strength in moderate, 16% in trained, 10% in advanced, and 2% with elite participants was noted.
  • With training, a shift from Type 2x fibers into Type 2a fibers demonstrates a greater fatigue resistance at similar force output.

• Power
  • Body weight is best for improving peak power output. Think of performing jump squats where the speed component is emphasized. Some sources state 30-60% of 1RM is optimal to produce power. Peak power in a squat is maximum at 56% of 1rm, while power cleans are closer to 80% 1rm.

• Local muscular endurance
  • Anaerobic training generates fatigue and metabolites inside the muscle cells. In response to the stimulus, there is improved buffering capacity, mitochondrial and capillary numbers, and metabolic enzyme activity. This improves the endurance of the muscle at an anaerobic intensity level.

• Body Composition 
  • Resistance training increases fat-free mass and may reduce body fat up to 9%. Anaerobic exercise builds lean mass which is metabolically expensive. Having more muscle increases daily metabolic rate, and energy expenditure during exercise.

• Aerobic capacity
  • In the untrained, there may be a slight increase in VO2 max. In the untrained, there is no significant impact.
  • Circuit training which elevates the heart rate using large volume and short rest can Improve VO2 max.

• Motor learning
  • As we move we stimulate our nervous system to move more efficiently. Resistance training has been shown to increase the efficiency or economy of things like jumping, running, and kicking.

• Programming anaerobic and aerobics
  • People have many opinions about mixing weights and cardio and there is some truth to both sides of the argument.
  • If you train 3 days resistance, 3 days aerobically, there does appear to be an interference effect with strength and power. And 3 days a week combined strength and aerobics has been shown to have less interference. The takeaway here is to rest to fully recover from the accumulated fatigue accrued during training. 
  • If you are a power athlete this antagonism is more meaningful. Power is negatively affected by aerobic endurance training. However, this only applies to individuals who are fixated on generating as much power as possible which is likely not you. In my opinion, a combination of both aerobics and anaerobic yields the best of both worlds.
    • Cardiovascular health is much more important to me than a minimal increase in power.

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Overtraining

Training frequency, volume, or intensity can all cause overtraining if dialed too high. Rest, sleep, nutrition, health status, injury, stress, and recovery all play a role in preventing overtraining.

• Overreaching or Functional Overreaching (FOR)
  • This is a short-term decrease in performance. Some may plan this intentionally before a taper with rest to allow a super-compensation in performance. With poor programming and insufficient recovery, this can lead to nonfunctional overreaching (NFOR). NFOR is when athletes cannot recover from extreme overreaching causing decreased performance for weeks or months.

• Overtraining Syndrome (OTS)
  • With prolonged overtraining, OTS may occur causing prolonged symptoms. You may notice burnout, overwork, staleness, overfatigue, and Inability to sustain high-intensity exercise when the training load is maintained. May be caused by progressively overloading too quickly. OTS may last as long as 6 months. There are two types of OTS.

• Sympathetic overtraining syndrome
  • This occurs first and results in sympathetic nervous system stimulation. This is your fight or flight response so you will have an increased hr, breathing rate, and reduced digestion.

• Parasympathetic overtraining syndrome
  • After the sympathetic syndrome, there is an increased PNS at rest and with exercise. This causes a chronic suppression of physiology. This would cause chronic fatigue and decreased performance. Sleep and emotional symptoms may occur with an increased risk of infection. Loss of appetite and increased exertion during training may be observed.
  • Hormonal signs of overtraining
    • A blunted risk in growth hormone, ACTH, LH, and FSH in response to training may occur. Decreased testosterone and IGF-1 may also occur causing worse recovery. 
  • Psychology of overtraining
    • • Mood and community involvement can be markers of overtraining. If the individual has poor confidence, experiences depression, irritability, and fatigue, their programming should be evaluated. Additionally, a referral to a healthcare professional may be warranted.

• Detraining
  • Refers to the decrease in performance when training ends. This can cause loss of muscle mass, reduction of capillary density, reduced enzymatic adaptations, and many others. This speaks to the principle of reversibility, which states that training adaptations can only be held with continual training. Strength is maintained for up to 4 weeks of inactivity, in athletes peak performance with eccentric force and sport-specific power may decline faster. The good news is that two weeks will not change 1rm significantly maybe 1-2%. In 2-3 months, the decreased strength is closer to 10% due to neural and atrophy detraining. Muscle fibers will decrease CSA by 6.4% in 2 weeks. With chronic detraining of 7 months, a 37.1% atrophy of fibers was seen in powerlifters.

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References: 

Haff G, Triplett T. 2016. Essentials of Strength Training and Conditioning. 4th ed. Champaign, Il: Human Kinetics.