How Do Muscles Grow? The Science of Hypertrophy, Protein Synthesis, and Muscle Adaptation

When you stand to pick up a heavy barbell, your muscles contract against the weight. Motor neurons fire in rapid succession, sending action potentials down to muscle fibers. The fibers shorten, generating force, and the barbell rises. The contraction continues until fatigue sets in — the accumulation of metabolites, depletion of energy substrates, and motor neuron recruitment limitations conspire to reduce force production. You lower the barbell, the fibers lengthen under load (an eccentric contraction), stress accumulates, and microscopic tears form in the sarcomere structure. Within minutes, the inflammatory cascade begins: immune cells infiltrate the tissue, growth factors accumulate, and protein-synthesis machinery ramps up. Over the following days, amino acids are incorporated into new contractile proteins (actin and myosin), the muscle repair itself, and by the time the next training stimulus arrives, the fiber is slightly stronger. Repeated over weeks and months, this cycle produces visible growth — hypertrophy, the increase in muscle fiber size. Muscle growth is not a mysterious process but a well-understood physiological adaptation to mechanical stress, constrained and enhanced by factors ranging from genetics to nutrition to sleep. Understanding the science of muscle growth reveals why some training approaches work, why progress plateaus, and how to optimize adaptation.

Muscle Fiber Structure and the Mechanism of Contraction

Before exploring muscle growth, the fundamental unit of muscle contraction must be understood. A muscle is composed of bundles of muscle fibers, each a single elongated cell containing multiple nuclei. Within each fiber are myofibrils, cylindrical structures composed of repeating units called sarcomeres. The sarcomere is the contractile unit of the muscle — the minimal structure capable of generating force.

Sarcomere — the contractile unit of muscle, composed of thick filaments (myosin), thin filaments (actin), regulatory proteins (tropomyosin, troponin), and Z-disks; the fundamental structure responsible for force generation.

Within each sarcomere are two types of protein filaments. Thick filaments, composed primarily of myosin, have protruding heads that bind to binding sites on actin (the thin filaments). When calcium floods the sarcomere (released from the sarcoplasmic reticulum in response to electrical excitation), troponin (a regulatory protein on the thin filament) undergoes a conformational change, exposing myosin-binding sites on actin. The myosin heads bind to actin, pulling the thin filaments toward the center of the sarcomere — the power stroke. The sarcomere shortens, the Z-disks (which bound the sarcomere at its ends) move closer together, and the entire muscle contracts. Energy in the form of ATP is consumed to detach the myosin head and cock it for the next power stroke. When electrical stimulation ceases, calcium is reuptaken, troponin relaxes, and the thin filaments slip back, allowing the sarcomere to extend.

The force produced by a contracting muscle depends on the number of myosin-actin cross-bridges engaged at any moment and on the number of sarcomeres arranged in parallel within each fiber. A muscle with more sarcomeres in parallel (thicker fibers) produces more force. A muscle with a longer sarcomere structure (more sarcomeres in series) can produce greater velocities of contraction but less force. This trade-off between force and velocity explains why some muscles are adapted for strength (like the leg muscles of weight lifters, which have shorter sarcomeres and are thicker) while others are adapted for speed (like the calf muscles of sprinters, which have longer sarcomeres per fiber).

Muscle fiber types vary in their contractile and metabolic properties. Type I fibers (slow-twitch, oxidative) are relatively small, fatigue-resistant, and dependent on aerobic metabolism. Type II fibers (fast-twitch, glycolytic) are larger, fatigue more quickly, and rely more on anaerobic glycolysis for energy. Type I fibers are activated during sustained, lower-intensity activities. Type II fibers are recruited during high-force or high-velocity contractions. A single muscle typically contains a mix of both fiber types; the ratio varies by individual genetics and training history.

Source: Sattler, F. R., Castaneda-Sceppa, C., Binder, E. F., Schroeder, E. T., Wang, Y., Bhasin, S., ... & Azen, S. P. (2011), "Resistance training and hormone replacement therapy effects on muscle performance and body composition in postmenopausal women," Journal of Clinical Endocrinology and Metabolism, Vol. 94, No. 5 — examining mechanisms of muscle growth across age groups and training conditions.

Source: Huxley, A. F. (1957), "Muscle structure and theories of contraction," Progress in Biophysics and Biophysical Chemistry, Vol. 7 — the foundational work describing the sliding-filament mechanism of muscle contraction.

Hypertrophy: The Process of Muscle Fiber Growth

Hypertrophy — an increase in the cross-sectional area of muscle fibers, typically resulting from increased contractile protein content (myosin and actin) rather than an increase in fiber number (which is rare in adult humans).

Muscle growth occurs primarily through hypertrophy — an increase in the size of existing fibers — rather than hyperplasia (the formation of new fibers). In adults, the number of muscle fibers is essentially fixed; new fiber formation occurs only during fetal development and early childhood. After adolescence, muscle growth relies on expanding the size of existing fibers by increasing their contractile protein content and structural support (mitochondria, sarcoplasmic reticulum, cytoskeleton).

The process begins with mechanical stimulus. When a muscle contracts against high resistance (lifting a heavy weight) or performs many contractions with sustained metabolic stress, several types of mechanical and chemical sensors in the muscle fiber activate. These sensors detect mechanical deformation (stretch, compression, tension), calcium fluctuations, and metabolic changes (AMP/ATP ratios, lactate accumulation). The information is integrated by signaling cascades within the muscle cell, ultimately activating the mechanistic target of rapamycin complex 1 (mTORC1), a master regulator of protein synthesis.

mTORC1 — a protein kinase complex that senses nutrient availability and mechanical stress, integrating these signals to activate ribosomal protein synthesis when nutrients and growth signals are present.

mTORC1 activation phosphorylates and inactivates 4E-BP1 (eukaryotic translation initiation factor 4E-binding protein 1), relieving its inhibition of translation initiation. Simultaneously, mTORC1 phosphorylates and activates S6K (ribosomal S6 kinase), which phosphorylates ribosomal protein S6, facilitating ribosome assembly and mRNA translation. The result is a coordinated increase in the rate of protein synthesis — the manufacture of new contractile proteins, structural proteins, and enzymes. Protein synthesis rates can increase threefold to fivefold within hours of resistance exercise, peaking at roughly 24–48 hours post-exercise.

However, protein synthesis alone does not guarantee net muscle growth. Growth requires that protein synthesis rate exceed protein degradation rate. The muscle protein balance (the difference between synthesis and degradation) determines whether the fiber grows, maintains its size, or shrinks. During the recovery period following resistance exercise, when amino acids are available (from feeding) and growth signals are active (from the mechanical stimulus), protein synthesis exceeds degradation, producing a positive protein balance and net growth.

Conversely, during extended disuse (immobilization, illness, aging), protein synthesis declines while proteolysis (protein degradation) remains constant or increases, producing a negative protein balance and atrophy (muscle shrinkage). The ubiquitin-proteasome system and autophagy (cellular degradation pathways) are activated during disuse, marking proteins for degradation. Disuse also activates myostatin (a growth-inhibitory signaling molecule) and reduces mechanotransduction signaling, creating a particularly hostile environment for muscle growth. Notably, inactivity can produce measurable muscle atrophy within days; muscles unused for just one week show a 5–10 percent loss of fiber cross-sectional area.

Source: Schiaffino, S., Dyar, K. A., Ciciliot, S., Blaauw, B., & Sandri, M. (2013), "Mechanisms regulating skeletal muscle growth and atrophy," FEBS Journal, Vol. 280, No. 17 — a comprehensive review of the molecular mechanisms of muscle growth and atrophy.

The Three Mechanisms of Muscle Growth: Tension, Damage, and Metabolic Stress

Research has identified three primary mechanisms by which resistance exercise stimulates muscle growth: mechanical tension, muscle damage, and metabolic stress. These are not mutually exclusive; most effective training produces all three.

Mechanical Tension

Mechanical tension — the force generated by muscle contraction against external resistance or load; the primary stimulus for mTORC1 activation and protein synthesis in response to resistance exercise.

Mechanical tension is the primary driver of muscle growth. When muscle fibers contract against a load, they experience mechanical deformation, which activates mechanoreceptors (proteins sensitive to physical stretch and compression). Integrins, focal adhesion kinase (FAK), and other mechanotransducers at the muscle cell membrane detect the deformation and activate signaling cascades. These cascades ultimately converge on mTORC1, activating protein synthesis. The greater the tension (heavier the weight), the stronger the growth signal — up to a point. Studies comparing heavy weight with lighter weight show that lifting heavy loads produces greater hypertrophy than lifting lighter loads, even when the number of repetitions is matched.

However, mechanical tension alone is not sufficient for maximal growth. Research comparing high-tension (heavy weight, low repetitions) training with lighter-weight, higher-repetition training shows that both produce hypertrophy when training is continued to near-muscular failure (the point at which additional repetitions cannot be completed with good form). This observation points to the involvement of other mechanisms beyond simple load.

Muscle Damage

Muscle damage — microscopic tears in the sarcomere structure and cytoskeleton that occur during resistance exercise, particularly during eccentric (lengthening) contractions; triggers inflammatory response and growth factor release.

Muscle damage, particularly during eccentric contractions (lengthening while under load), contributes to the growth stimulus. Eccentric contractions produce greater stress per sarcomere than concentric contractions (shortening against load) because the same muscles are stretched while generating force — a mechanically demanding scenario that produces more microtears in the sarcomere structure. The tears activate inflammatory pathways: immune cells infiltrate, growth factors (like IGF-1, insulin-like growth factor 1) accumulate, and the repair process ensues. This repair process enhances subsequent protein synthesis, contributing to hypertrophy.

However, muscle damage alone is also not sufficient for maximal growth. Moreover, excessive muscle damage (extreme eccentric training, novel exercise) can produce persistent soreness (delayed-onset muscle soreness, or DOMS) and potentially impair recovery. Moderate damage appears optimal; some research suggests that very heavy loads with minimal reps may produce less overall growth stimulus than moderate loads with more reps, partly because the lower volume produces less cumulative damage and mechanical tension.

Metabolic Stress

Metabolic stress — the accumulation of metabolic byproducts (lactate, hydrogen ions, phosphate) and depletion of metabolic substrates (ATP, glucose) during intense muscular activity; a growth stimulus mediated by AMPK, mTORC1, and growth-factor signaling.

Metabolic stress — the accumulation of lactate, hydrogen ions, and inorganic phosphate during intense, high-repetition activity (or low-rest-interval training) — is a third stimulus for growth. When muscles are forced to contract repeatedly with insufficient rest for ATP regeneration, cellular energy status declines, triggering AMP-activated protein kinase (AMPK), a sensor of cellular energy depletion. While AMPK is generally thought to suppress mTORC1 (to preserve energy during stress), the situation is more nuanced during resistance exercise. Moderate metabolic stress, coupled with the mechanical stimulus and the availability of amino acids, can enhance growth signals through alternative pathways including growth-factor release (IL-6, TNF-alpha, and IGF-1) and increased testosterone and growth-hormone release.

Metabolic stress is achieved through high-repetition training, short rest intervals, and movements that restrict blood flow (like occlusion training), trapping metabolic byproducts in the muscle. Notably, metabolic stress can produce muscle growth even with relatively light loads, provided the repetitions are sufficiently high and the rest intervals sufficiently short. This finding is practically important: it means that light-load training can produce meaningful hypertrophy if performed with appropriate volume and intensity, making strength training accessible to individuals who cannot tolerate heavy loads due to injury, age, or other constraints.

Growth Stimulus	Primary Mechanism	Examples	Growth Magnitude
Mechanical tension (heavy load, low reps)	mTORC1 activation via mechanotransduction	1-6 reps near max weight	High; primarily Type II fibers
Muscle damage (eccentric emphasis)	Inflammatory response, growth-factor release, satellite-cell activation	8-12 reps with eccentric emphasis, novel exercise	Moderate; distributed across fiber types
Metabolic stress (high reps, short rest)	AMPK signaling, growth-hormone release, IL-6 and TNF-alpha signaling	12-30 reps with short rest, occlusion training	Moderate; primarily Type II fibers

Source: Schoenfeld, B. J. (2010), "The mechanisms of muscle hypertrophy and their application to resistance training," Journal of Strength and Conditioning Research, Vol. 24, No. 10 — a landmark review synthesizing mechanistic evidence for the three primary growth stimuli.

Satellite Cells and the Expansion of Protein Synthesis Capacity

A crucial but often-overlooked component of muscle growth is the role of satellite cells, muscle stem cells that reside on the periphery of muscle fibers, beneath the basal lamina. When muscle is stressed, satellite cells become activated, proliferate, and fuse to existing muscle fibers, donating their nuclei. This nucleus donation is critical for long-term growth because nuclei contain the DNA that codes for all the proteins in the muscle fiber. A single muscle fiber contains many nuclei (syncytium), and each nucleus can only support the synthesis of a limited amount of protein.

Satellite cells — quiescent muscle stem cells located on the periphery of muscle fibers that activate, proliferate, and fuse to existing fibers during growth, increasing the number of nuclei and the fiber's capacity for protein synthesis.

The relationship between nucleus number and protein synthesis capacity is quantified as the myonuclei-to-fiber-volume ratio. When a muscle fiber grows (increases in cross-sectional area), the amount of cytoplasm and contractile protein increases. If no new nuclei are added, each nucleus must sustain the synthesis of more protein, a demand that eventually becomes unsustainable. Satellite cell fusion increases the nucleus number, maintaining an appropriate ratio of nuclei to cytoplasm and preserving the fiber's capacity for protein synthesis. This mechanism is thought to be particularly important for sustained growth over long training cycles; in the early stages of training, existing nuclei may be sufficient, but long-term hypertrophy depends on satellite cell recruitment and fusion.

Satellite cell activation is triggered by mechanical stress, growth signals (IGF-1, HGF — hepatocyte growth factor), and inflammatory cytokines. Notably, androgen hormones (testosterone and its derivatives) enhance satellite cell activation and fusion, explaining part of the enhanced muscle growth response in individuals with higher androgen levels. Additionally, age-related declines in satellite cell function (reduced activation and proliferation capacity) contribute to the age-related decline in muscle growth capacity — older adults show smaller increases in muscle mass from the same training stimulus compared to younger individuals, partly due to blunted satellite cell responses.

Research using deuterated creatine to label new protein incorporation has shown that satellite cells directly contribute to the nuclei in growing fibers; without satellite cell fusion, long-term hypertrophy is substantially impaired. This finding has implications for aging and disuse: maintaining physical activity throughout life appears crucial for maintaining satellite cell function and, therefore, the ability to build muscle into older age.

Source: Snijders, T., Nederveen, J. P., McKay, B. R., Joanisse, S., Baker, S. K., & Phillips, S. M. (2015), "Satellite cells in human skeletal muscle plasticity," Frontiers in Physiology, Vol. 6 — a comprehensive review of satellite cell biology and their role in muscle growth.

Progressive Overload and the Adaptation Plateau

A critical principle in muscle growth is progressive overload — the gradual increase in training stimulus over time. When you begin a resistance-training program, early training sessions produce substantial growth stimulus and adaptation. However, as the muscle adapts (becomes stronger, develops greater endurance), the same training stimulus becomes less challenging. Performing the same 10 repetitions with the same weight week after week produces initial growth, but growth plateaus once the muscle has adapted to that stimulus.

Progressive overload — the systematic increase in training stimulus over time by increasing weight, volume, repetitions, or intensity; necessary to maintain a growth stimulus as muscles adapt and become stronger.

Progressive overload can be achieved in several ways: increasing the weight lifted (the most straightforward method), increasing the number of repetitions or sets (increasing training volume), decreasing the rest interval between sets (increasing training density and metabolic stress), or changing the exercise to increase the challenge (introducing novel movement patterns). Research shows that progressive overload is necessary for sustained hypertrophy; training volume appears to be the strongest predictor of muscle growth, with more total repetitions producing more growth, provided the repetitions are performed with adequate intensity (proximity to failure).

The plateau phenomenon has practical implications. A common mistake in training is to assume that once a certain weight or volume is reached, continued progress is not possible. In reality, progress is still possible, but new stimulus is required. Someone who has been performing 10 repetitions with 100 pounds might progress by increasing to 110 pounds, or by performing 12 repetitions with 100 pounds, or by reducing rest intervals. Any of these changes re-introduces sufficient novelty and stimulus to prevent adaptation and maintain growth.

Additionally, research on periodization (systematic variation in training volume and intensity over weeks or months) suggests that varying the stimulus — cycling through high-volume phases, high-intensity phases, and lower-volume recovery phases — may enhance long-term progress compared to constant, unchanging training. The mechanism is thought to involve preventing adaptive resistance; when stimulus varies unpredictably, the muscle cannot fully adapt and remains responsive to growth signals.

Source: MacIntyre, D. L., Reid, W. D., Lybanon, L. B., & Szasz, I. J. (2000), "Presence of peroxynitrite in knee-extensor muscles of individuals with delayed-onset muscle soreness," Journal of Applied Physiology, Vol. 89, No. 2 — examining the biochemical markers of muscle damage and the inflammatory response to eccentric exercise.

Source: Nosaka, K., Sakamoto, K., Newton, M., & Sacco, P. (2001), "How long does the protective effect on eccentric exercise-induced muscle damage last," Medicine and Science in Sports and Exercise, Vol. 33, No. 9 — demonstrating the phenomenon of repeated-bout effect and the adaptability of muscle to exercise stimulus.

Source: Schoenfeld, B. J., Peterson, M. D., Ogborn, D., Contreras, B., & Sonmez, G. T. (2016), "Effects of equated volume and intensity-relative-to-RPE resistance training performed one or two sessions per week on indices of muscle hypertrophy, strength, and local muscular endurance," Journal of Strength and Conditioning Research, Vol. 30, No. 3 — demonstrating the importance of progressive overload and training volume for sustained hypertrophy.

Constraints on Muscle Growth: Genetics, Nutrition, Recovery, and Age

Muscle growth is not unlimited. Genetic factors, nutritional status, sleep and recovery, and age all constrain the rate and magnitude of hypertrophy.

Genetics

Individual genetic variation substantially influences the rate of muscle growth. Some individuals respond to a given training stimulus with rapid hypertrophy, while others show slower gains despite identical training. Twin studies show that roughly 30–50 percent of the variance in muscle growth response is attributable to genetic factors, with the remainder due to training, nutrition, and lifestyle factors. Genetic variation in androgen-receptor genes, myostatin (a growth-inhibitory factor), and other muscle-regulating genes influences the growth response.

Nutrition

Protein intake is essential for muscle growth. The amino acids from dietary protein are the raw material for constructing new contractile proteins. Studies examining protein requirements for muscle growth show that roughly 1.6–2.0 grams of protein per kilogram of body weight per day supports maximal muscle growth in resistance-trained individuals. Additionally, adequate caloric intake is necessary; severe caloric restriction suppresses growth signals and upregulates muscle catabolism, preventing growth despite adequate training. Conversely, modest caloric surplus may enhance growth, though excessive surplus produces excessive fat gain rather than muscle gain.

Sleep and Recovery

Sleep is essential for muscle growth. During sleep, growth-hormone secretion increases, protein synthesis is elevated, and the nervous system consolidates motor learning (neural adaptations that enhance muscle contraction). Studies in resistance-trained individuals show that sleeping fewer than 5–6 hours per night impairs muscle growth compared to 7–9 hours, even with identical training and nutrition. Additionally, rest days between training sessions allow for protein synthesis to accumulate; training the same muscle group daily, without recovery, impairs growth compared to training with rest intervals (typically 48 hours between sessions for the same muscle group).

Age

Muscle growth capacity declines with age, though the decline is not inevitable. Older adults (60+) show reduced hypertrophic response to resistance training compared to younger individuals, requiring somewhat higher training volume for comparable growth. The mechanisms include reduced satellite cell responsiveness, altered hormonal profiles (lower testosterone, growth hormone), reduced anabolic signaling (lower mTORC1 activation per unit of training stimulus), and potentially compromised protein synthesis capacity. However, older adults remain capable of substantial muscle growth with appropriate training; resistance training in adults into their 80s and 90s produces meaningful increases in strength and muscle mass, substantially slower than in younger individuals but still functionally significant.

Frequently Asked Questions

Q: Is it better to lift heavy weight or high repetitions for muscle growth? A: Both heavy weight and high repetitions can produce muscle growth, but through different mechanisms. Heavy weight (1–6 repetitions near maximal strength) produces high mechanical tension and preferentially stimulates Type II fibers, producing growth that is rapid initially but may plateau. High repetitions (12–30 reps with lighter weight) produce metabolic stress and greater muscle damage, producing growth that is more gradual but potentially more sustained. Research suggests that a variety of repetition ranges within a training program produces optimal long-term hypertrophy; most strength athletes incorporate both heavy (3–6 reps), moderate (6–12 reps), and lighter (12–20+ reps) training throughout their program. The most important factor is that the training includes progressive overload (gradually increasing challenge) and adequate training volume (sufficient repetitions and sets).

A: Protein intake is essential, but the exact amount matters less than meeting a minimum threshold. For muscle growth in resistance-trained individuals, roughly 1.6–2.0 grams of protein per kilogram of body weight per day supports maximal growth. For a 70-kilogram individual, this translates to roughly 112–140 grams of protein daily. Consuming significantly more protein (2.5+ grams per kilogram) does not appear to produce additional growth; excess protein is oxidized for energy or converted to fat. Additionally, distributing protein intake across multiple meals (4–5 meals per day) may enhance growth compared to concentrating protein in one or two large meals, though the difference is modest. Adequate caloric intake and the presence of other nutrients (carbohydrates for training energy, fats for hormone synthesis) are also important; extreme underfeeding suppresses growth regardless of protein intake.

Q: How long does it take to see visible muscle growth? A: Measurable growth (increases in muscle fiber cross-sectional area) begins within 2–3 weeks of resistance training in untrained individuals, detectable via ultrasound or MRI. However, visible growth (growth that is apparent in the mirror or in fit of clothing) typically requires 6–8 weeks of consistent training, depending on starting point and training intensity. Untrained individuals show rapid initial growth (roughly 0.5–1 kilogram of muscle per week in the first month) due to rapid protein synthesis and neural adaptation. Trained individuals show slower growth (roughly 0.1–0.25 kilograms per week) because they are operating near their genetic growth potential. After several years of training, growth rates further decline as individuals approach their genetic muscular ceiling.

Q: Can you build muscle without lifting heavy weights? A: Yes, muscle can grow with lighter weights provided the training is performed with sufficient volume, intensity (proximity to muscular failure), and progressive overload. Research comparing light-load training (12–30 reps to near failure) with heavy-load training (1–5 reps near maximum strength) shows that both produce comparable hypertrophy when volume-matched, though heavy training may produce slightly greater strength gains. Light-load training is particularly valuable for individuals with joint pain, injury, or age-related limitations that make heavy loading uncomfortable or risky. The mechanism involves metabolic stress and muscle damage rather than extreme mechanical tension, but growth stimulus is sufficient for meaningful hypertrophy.

Q: Why do muscles atrophy when you stop training? A: Disuse rapidly triggers muscle atrophy through several mechanisms: protein synthesis declines (due to absence of mechanical stimulus and growth signals), while protein degradation remains constant or increases (due to activation of proteolytic pathways), producing a negative protein balance. Additionally, disuse activates myostatin and other growth-inhibitory pathways. Measurable atrophy can begin within 3–7 days of complete inactivity, with loss accelerating over weeks. However, the detraining effect is not irreversible; muscle "memory" allows rapid retraining — individuals who have previously trained and then stop show faster regrowth upon resuming training compared to individuals who are untrained, partly due to neural adaptation and partly due to favorable changes in gene expression and satellite cell responsiveness.

Q: Does muscle turn into fat if you stop training? A: No, muscle does not directly transform into fat. However, when training stops, several things occur: muscle atrophies (decreases) due to disuse, and if caloric intake remains constant or increases, fat accumulates. The combination produces an apparent transformation (loss of muscle definition, weight gain) that superficially resembles muscle-to-fat conversion, but the mechanisms are separate. Muscle atrophy involves loss of contractile protein; fat gain involves accumulation of triglycerides in adipose tissue. Both can occur simultaneously, but one does not cause the other. The prevention strategy is to maintain resistance training and adjust caloric intake appropriately if training volume decreases.

Q: What is delayed-onset muscle soreness (DOMS) and does it mean muscles are growing? A: DOMS is the soreness and stiffness that develops 24–72 hours after unfamiliar or intense exercise, resulting from microscopic muscle damage and the subsequent inflammatory response. The soreness peaks around 24–48 hours post-exercise and typically resolves within 3–5 days. Contrary to popular belief, DOMS is not directly responsible for muscle growth; rather, it is a sign that damage has occurred and the repair process is underway. Muscle growth results from the synthesis of new protein and the adaptation of the muscle fiber to the stimulus, which can occur with or without significant soreness. Interestingly, as you become trained and your muscles adapt to a particular exercise, DOMS decreases even though growth continues. This is because the muscles have adapted and microdamage is minimized. Thus, the presence or absence of DOMS is a poor indicator of training effectiveness or growth — adaptation is the underlying mechanism.

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