Most Important Factors Affecting Muscle Growth

Testosterone and Muscle Growth

When you’re natural, your body’s production of testosterone is limited and decreases with age, setting a ceiling for potential muscle growth. Lower testosterone levels explain why the average woman is generally smaller and weaker than the average man. However, when women use performance-enhancing drugs, their physiques can surpass those of natural males, showcasing the power of hormones.

For example, female pros often achieve shredded 15-inch arms, a size many true natural bodybuilders can never reach. Fat, bulky arms don’t count—only lean, defined measurements matter. No amount of training or eating can override the hormonal constraints your body imposes. Lifting weights might boost testosterone slightly, but not enough to achieve dramatic growth. It’s akin to trying to get rich by selling newspapers—there’s a limit to what’s possible without the proper mechanisms in place.

Changing routines—volume, intensity, or reps—won’t alter this reality. Hormones remain the key determinant, a fact often ignored by fitness marketers and influencers who focus on sellable concepts like protein intake and training techniques.

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Frame

Your skeletal frame is a major determinant of how much muscle you can build naturally. A person with a narrow structure and thin bones simply cannot carry as much muscle as someone with broad shoulders and robust joints. Unfortunately, your frame is immutable. Even steroids can’t completely mask the limitations of a smaller skeleton, which is why some top bodybuilders are criticized for lacking width. By default, people with thicker frames appear larger, even without training.

Height and muscle thickness are not synonymous. While taller individuals might carry more lean mass overall, they require significantly more muscle to “fill out” their frames compared to shorter people. Frame size, defined by shoulder width and bone thickness, is what truly impacts appearance—not height.

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Muscle Insertions

The length of your muscles and tendons affects how much they can grow. Long tendons and short muscle bellies limit growth potential, often making these areas appear weaker. Conversely, individuals with longer muscle bellies naturally look fuller and have more potential for growth.

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Wider Availability and Innovation

By the 1940s, steroids became cheaper as diosgenin-based synthesis streamlined production. Companies like Syntex SA, founded by Marker, played a crucial role in distributing hormonal drugs in the U.S. Between 1948 and 1955, Searle Pharmaceuticals synthesized over 1,000 steroid variants in an effort to reduce androgenic side effects.

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Training Response

Training response refers to how your body adapts to resistance training. Given identical routines, some individuals will develop larger, fuller muscles than others. Factors like frame and muscle insertions also influence training outcomes by affecting biomechanics and exercise technique. For example, some lifters focus more on their torsos, while others emphasize limb movement.

Certain people, like “strong skinny boys,” develop significant strength with minimal visible hypertrophy. For instance, a lifter might deadlift double their initial weight without a noticeable change in appearance. The body adapts to training for survival rather than aesthetic goals, prioritizing functional efficiency over size.

Age

Age is a critical factor in muscle growth. Peak physical capacity occurs during youth, after which a gradual decline begins. Despite claims that “40 is the new 20,” this applies more to general appearance than physical performance. Testosterone levels naturally decrease with age, making it harder to gain muscle over time. Claims of dramatic natural transformations in older individuals are often the result of steroid use rather than training alone.

Stress

Excess stress, particularly from cortisol, can inhibit muscle growth. Individuals in low-stress environments, with ample resources and support, have an anabolic advantage over those facing high levels of mental or physical pressure. Common sources of stress include poor health, financial struggles, loneliness, and dissatisfaction with one’s career.

Muscle Fiber Types

Muscle fibers are categorized as fast or slow twitch. Fast-twitch fibers, used for explosive movements, have greater growth potential, while slow-twitch fibers, designed for endurance, are less prone to hypertrophy. Some training methods target slow-twitch hypertrophy, but their effectiveness is limited.

Training, Nutrition, and Recovery

Training is essential for muscle growth, but genetics largely dictate how much muscle you can gain. Proper nutrition, especially adequate protein intake, supports muscle repair and growth. However, natural lifters don’t need excessive protein—120 grams per day is typically sufficient. Overloading on protein doesn’t translate to additional muscle gain if the body lacks the capacity to utilize it effectively.

Sleep and recovery also play a role, but over-sleeping won’t lead to dramatic growth. Maintaining general health is vital, as illness can hinder progress by disrupting training, eating, and recovery.

Types of Frames

Here’s a concise breakdown of the four main frame types based on wrist size:

1. Small Frame:
   • Wrist size: 5.5 to 6.5 inches (13.97 cm to 16.51 cm)
   • Characteristics: Lighter build with a slender skeletal structure.
2. Medium Frame:
   • Wrist size: 6.5 to 7.5 inches (16.51 cm to 19.05 cm)
   • Characteristics: Average skeletal structure, balanced proportions.
3. Big Frame:
   • Wrist size: Between 7.5 and 8.5 inches (19.05 cm to 21.59 cm)
   • Characteristics: Heavier skeletal structure, broader build.
4. Ultra-Big Frame:
   • Wrist size: 8.5 inches or more (21.59 cm or larger)
   • Characteristics: Extremely rare, large and robust skeletal structure.

This classification provides a useful guide to understanding body structure and its implications on weight and proportions.

Example

For someone who is 6’2” (188 cm) tall with good genetics, the 70s bodybuilding standard would be Arnold Schwarzenegger, often regarded as having the best overall genetics in bodybuilding history. Arnold maintained a weight of 235 lbs (106.8 kg) at 6’2” during most of his career. Subtracting 40–50 lbs from this gives a natural lifter with good genetics a potential lean weight of 185–195 lbs (84–88.6 kg). Exceeding this weight while maintaining low body fat is unnatural in nearly all cases, except for extraordinarily rare genetic anomalies.

Not everyone has ideal bodybuilding genetics. Factors like frame size and bone structure significantly affect weight. For example, two men of the same height and body fat percentage can weigh differently due to variations in skeletal size.

Small Frame

If you have a small frame, your weight will likely be on the lower side. The author, at 6’1” (185 cm) with wrists measuring 6.25 inches (15.87 cm), notes being lighter compared to others of similar height. Individuals with thinner frames should adjust their target weight downward. For example, Arnold’s frame (7.5-inch wrists) suggests a target weight of 195 lbs (88.6 kg), but those with smaller frames might reduce this by 5–10%, depending on wrist size.

• A 10% reduction gives a target of 175.5 lbs (79.72 kg).
• Subtract further for additional genetic factors:
  1. Long tendons and short muscle bellies: If this applies to multiple areas (e.g., arms, hamstrings, calves), subtract 5 lbs (2.2 kg).
     Result: 170 lbs (77 kg).
  2. Low testosterone: Only consider this for significantly low levels. Subtract another 5 lbs.
     Result: 165 lbs (75 kg).
  3. Poor training response: If gains are minimal despite consistent training, subtract another 5 lbs.
     Final result: 160 lbs (72.7 kg).

Thus, a 6’2” man with a small frame and unfavorable genetic traits might weigh around 160 lbs in lean condition.

Medium Frame

Arnold’s medium frame and 7.5-inch wrists align with a target weight of 195 lbs (88.6 kg). For a medium-framed individual:

• Start at 195 lbs.
• Subtract 5 lbs for each disadvantage:
  1. Long tendons and short muscle bellies: 190 lbs (86 kg).
  2. Low testosterone: 185 lbs (84 kg).
  3. Poor training response: 180 lbs (81.8 kg).
     Thus, a medium-framed individual might achieve 180 lbs (81.8 kg) under similar conditions.

Extra-Large Frame

For a man with a large frame (e.g., 9-inch wrists, exceptionally rare), add 5% to Arnold’s starting weight:

• Start at 205 lbs (93 kg).
• Subtract 5 lbs for each disadvantage:
  1. Long tendons and short muscle bellies: 200 lbs (91 kg).
  2. Low testosterone: 195 lbs (88.6 kg).
  3. Poor training response: 190 lbs (86 kg).

Thus, a man with a large frame but poor genetic factors might reach 190 lbs (86 kg) in lean condition. However, most people fall into the small or medium frame categories.

If we determine the typical weight range for a 6’2” (188 cm) tall man, factoring in good or bad genetics (160–205 lbs / 72.7–93 kg), we can extrapolate these values to other heights using a simple adjustment. Generally, an inch (2.54 cm) of height correlates to a weight difference of about 6 lbs (2.72 kg) for men. By adding or subtracting 6 lbs (2.72 kg) from the reference weights of 205 lbs (93 kg) and 160 lbs (72.7 kg), we can calculate equivalent weight ranges for other heights.

Here is the adjusted table:

Height	Weight Range
6’2” (188 cm)	160–205 lbs / 72.7–93 kg
6’1” (185 cm)	154–199 lbs / 70–90.5 kg
6’0” (183 cm)	148–193 lbs / 67–87.7 kg
5’11” (180 cm)	142–187 lbs / 64.5–85 kg
5’10” (178 cm)	136–181 lbs / 61.8–82 kg
5’9” (175 cm)	130–175 lbs / 59–79.5 kg
5’8” (173 cm)	124–169 lbs / 56–77 kg
5’7” (170 cm)	118–163 lbs / 53.6–74 kg
5’6” (168 cm)	112–157 lbs / 51–71 kg
5’5” (165 cm)	106–151 lbs / 48–68.6 kg

To calculate for heights not listed, simply add or subtract 6 lbs (2.72 kg) for every inch (2.54 cm) from the weight range of the nearest listed height.

While these ranges might stir some debate or emotional reactions, they represent a general guideline and move us closer to understanding natural weight benchmarks.

How Much Mass Can You Add as a Natural?

Until you commit fully to lifting, you remain an untrained version of yourself, serving as your starting point. The untrained state generally falls into three categories: skinny, average, and power-fatso. The “skinny” group includes malnourished individuals, “average” refers to those who are neither notably thin nor overweight, and “power-fatso” describes obese individuals with red, bloated faces.

Extremely skinny beginners tend to see larger potential gains, while power-fatsos achieve less lean body mass due to their higher starting levels. As a baseline, we’ll use the “average” untrained state. Once this average state is reached through dieting, most people seldom gain more than 30lbs (13.5kg) of lean mass. While you can keep adding fat indefinitely, that’s not the goal here.

Why is 30lbs (13.5kg) the limit?

The typical lean, untrained male of average height weighs around 130-160lbs (59-72kg). Adding over 30lbs of muscle to this base would push you into bodybuilding proportions. Achieving even this amount requires highly favorable conditions for growth, which is why it’s unrealistic to believe that most men can exceed 200lbs (91kg) naturally while remaining lean—unless they’re exceptionally tall (over 6’3″/190cm) or obese.

The Steve Reeves Debate

Steve Reeves, a 6’1″ (185cm) bodybuilder weighing 215lbs (97.7kg), achieved his fame in an era predating widespread steroid use. However, anabolic steroids had already emerged by the 1930s. Human trials involving testosterone propionate began in 1937, with its mention in a weightlifting magazine as early as 1938. Reeves won Mr. America in 1947—ten years after steroids became a reality. While there’s no definitive proof that Reeves used them, it’s plausible based on available information and other accounts.

How Long Will It Take to Reach Natural Gains?

Muscle growth isn’t infinite or linear. Your most significant gains occur during the first 18 months of serious, structured training. This means lifting with purpose, tracking progress, and following a clear plan. Each workout should push you closer to measurable improvements, whether by increasing weight or repetitions. Simply going through the motions won’t yield results.

Nutrition and Caloric Needs

Proper nutrition is crucial. While individual requirements vary, most people won’t need more than 2500-2700 calories daily unless they aim to gain excess fat. A simple caloric formula by Lyle McDonald is useful:

• Weight Loss: 10-12 calories per pound of body weight.
• Maintenance: 14-16 calories per pound of body weight.
• Weight Gain: Add 200-500 calories to maintenance levels.

For example:

• A 190lb (86kg) man aiming to lose weight needs 1900-2280 calories.
• A 150lb (68kg) man maintaining weight needs 2100-2400 calories.
• To gain weight, that same 150lb man would need 2300-2600 calories.

Lower values suit slower metabolisms, while higher needs apply to more active individuals. However, given our largely sedentary modern lifestyle, most people fall on the lower end. Overeating can lead to rapid fat gain, as I learned during my own experience consuming 3000-4000 calories daily. I gained 1-2lbs (0.5-1kg) per week—mostly as fat.

Conclusion

Most growth factors—such as genetics, frame, and hormonal profile—are beyond control. While training and nutrition are important, they cannot override these genetic limitations. Hard work in the gym rarely trumps natural talent. Much like beauty, muscle growth is largely predetermined by genetics. Those who are naturally gifted will always have an edge, even with minimal effort.