How much does muscle mass growth actually differ between people?

Studies show a wide range of hypertrophy. For example, one study found that the bottom quartile of responders saw no increase in quad fiber cross-sectional area, while the top quartile saw over a twofold increase compared to the average.

Is it normal to see very little strength gain despite training consistently?

Yes, it's normal. Research indicates substantial variability; within two standard deviations of the mean, strength gains can range from significant increases to even slight decreases, even for dedicated trainees.

Are genetics the main reason for differences in training response?

Genetics play a significant role, contributing to inherent differences in how well individuals respond to training stimuli. However, other factors like lifestyle, nutrition, and recovery also have a considerable impact.

How much can aerobic fitness gains vary between individuals?

The Heritage Study showed significant variability in VO2 max gains. While the average gain was around 400 mL, the best responders increased their VO2 max by over a liter per minute, about two and a half times the average.

Can measurement error explain differences in training progress?

While measurement error and day-to-day fluctuations can affect results, they cannot account for the large magnitude of differences observed between individuals' training responses. True biological variation is the primary driver.

What are strength standards and are they useful?

Strength standards are tables estimating strength levels based on training duration. They are considered nearly worthless outside of competitive powerlifting contexts, as they often ignore the significant individual variability in strength gains.

Key Moments

How much do muscle growth and strength gains differ between people?

Stronger By Science

Sports3 min read35 min video

Oct 5, 2022|6,878 views|260|51

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Key Moments

TL;DR

Individual responses to training vary greatly due to genetics, lifestyle, and biology.

Key Insights

There is significant variation in muscle growth and strength gains among individuals, even with identical training programs.

Genetics plays a role, but lifestyle factors like nutrition, sleep, and stress also influence training response.

Studies show ranges from no gains to over 50% increases in muscle size and significant strength differences.

Aerobic fitness also demonstrates similar variability in response to training programs.

Strength standards tables can be misleading as they don't account for individual response variability.

Measurement error and day-to-day fluctuations exist but do not explain the full extent of response differences.

THE EXTENT OF INDIVIDUAL VARIATION

This discussion focuses on the substantial differences in how individuals respond to training, encompassing muscle growth, strength gains, and general fitness improvements. Many people underestimate this variability, leading to self-doubt when their progress doesn't match social media examples or averages. The aim is to provide a clearer understanding of expected responses, offer peace of mind to those who might be 'slower' responders, and help individuals better interpret their own training outcomes and those of others.

STUDIES ON MUSCLE GROWTH VARIABILITY

Research highlights significant differences in muscle hypertrophy. A study by Bamman et al. (2007) involving 66 participants over 16 weeks showed that the bottom quartile of responders experienced no average increase in quad muscle fiber cross-sectional area. In contrast, the middle 50% saw an average increase of about 1,000 square micrometers, and the top quartile (75th-100th percentile) saw over 2,000 square micrometers. This indicates a twofold difference between average and higher responders, with outliers experiencing even greater gains.

STRENGTH GAINS AND AEROBIC RESPONSE VARIABILITY

Similar large variations are observed in strength gains. A study by Huble et al. (2005) with 585 participants found that while the average increase in biceps cross-sectional area was 15-20%, some individuals experienced decreases, and others saw gains exceeding 55%. Strength gains followed a similar pattern, with most experiencing around 20% improvement, but some seeing increases of 70-90% and one outlier up to 145%. Aerobic fitness, as studied in the Heritage study, also shows considerable variability, with gains in VO2 max ranging from decreases to over a liter per minute, approximately 2.5 times the average gain.

THE ROLE OF GENETICS AND LIFESTYLE

A primary contributor to this variability is genetics, although precise heritability estimates are complex to determine. Studies on related individuals (twins, siblings) show more similar training responses compared to unrelated individuals, strongly suggesting a genetic component. Beyond genetics, numerous lifestyle factors significantly influence training outcomes. These include adequate nutrition, sufficient sleep, effective stress management, and having enough time dedicated to training and recovery. These elements collectively shape an individual's physiological response.

BIOLOGICAL MARKERS AND MEASUREMENT CHALLENGES

Specific biological factors within the body also predict hypertrophy responses. These include satellite cell and myonuclei responses, specific microRNA expressions, ribosome biogenesis (essential for protein synthesis), and Androgen receptor density. While these point to underlying physiological differences, it's crucial to acknowledge the impact of measurement error and day-to-day biological fluctuations. A bad testing day can mask real gains, but the magnitude of observed differences far exceeds what can be attributed solely to such errors.

IMPLICATIONS FOR STRENGTH STANDARDS

The significant individual variability challenges the utility of generic strength standards tables for most individuals outside of competitive settings. These tables often assume strength is solely a function of training duration, neglecting individual response differences. An individual who trains diligently for years but responds poorly genetically or biologically may appear to be a novice on such a chart, leading to discouragement. Understanding that progress varies naturally is key to setting realistic expectations and maintaining motivation.

Mentioned in This Episode

●Companies

●Studies Cited

●Concepts

Variability in Muscle Cross-Sectional Area Gains (Different Studies)

Data extracted from this episode

Response Group	Bauman et al. (2007) - Quad Fiber CSA Change (sq micrometers)	Huble et al. (2005) - Biceps Fiber CSA Change (%)
Bottom Quartile (Worst Responders)	~0	Small Decrease
Mid-Range (Modest Responders, 25th-75th percentile)	~1000	~15-20%
Top Quartile (Best Responders, 75th-100th percentile)	>2000	>55%
Individual Best Response (Bauman et al.)	3200-3300	N/A

Variability in Strength and Aerobic Fitness Gains

Data extracted from this episode

Measure	Study	Average Change	Worst Response	Best Response	Ratio of Best to Average
Elbow Flexion Strength (MVC)	Huble et al. (2005)	~20%	Small Decrease	70-90% (one subject 145%)	~3.5-4.5x
Absolute VO2 Max	Heritage Study (Bouchard et al., 1999)	~400 mL	Small Decrease	>1000 mL	~2.5x

Variability in Strength Gains Based on Cohen's DZ

Data extracted from this episode

Metric	Value	Interpretation
Weighted Average Cohen's DZ	1.6	Indicates substantial variability in strength gains across studies.
Within 1 Standard Deviation (DZ=1.6, Avg Gain=20kg)	7.5 kg (low end) to 32.5 kg (top end)	More than a four-fold difference in gains.
Within 2 Standard Deviations (2.5th - 97.5th percentile)	-5 kg (decrease) to 45 kg (increase)	Represents the range for most 'normal' responses.

Squat 1RM Variability After 6-12 Months of Training (Stronger By Science Audience Survey)

Data extracted from this episode

Group	Average 1RM Squat (kg / lbs)	Standard Deviation (kg / lbs)	Range (within +/- 2 SDs)
Men	~150 kg / 330 lbs	~35 kg / 77 lbs	80 kg (176 lbs) to 220 kg (485 lbs)
Women	~90 kg / 200 lbs	N/A	30 kg (66 lbs) to 150 kg (330 lbs)

Common Questions

Response to training varies significantly between individuals due to a combination of factors, primarily genetics, but also influenced by nutrition, sleep, stress, lifestyle, and underlying biological responses like satellite cell and ribosome activity.

Topics

Training Variability Trainability Measurement Error

Mentioned in this video

Studies & Research

Huble et al. (2005)

A large study examining variability in muscle size and strength gains following unilateral resistance training over three months, showing a wide range of biceps cross-sectional area increases and elbow flexion strength changes.

Bouchard et al. (1999)

A paper resulting from the Heritage Study, focusing on familial aggregation of VO2 max response to exercise training in previously sedentary subjects.

Barbalia investigation

An investigation that analyzed data from 83 studies to quantify the typical variability seen in strength gains after resistance training programs, using Cohen's DZ values.

Bauman et al. (2007)

A study on cluster analysis and myogenic gene expression related to myofiber hypertrophy, highlighting variability in quad fiber cross-sectional area gains after 16 weeks of training.

Concepts

Androgen receptor density

Mentioned as a factor that seems to be predictive of hypertrophy gains, whereas Androgen levels themselves might not be as predictive.

myokine

Myokine responses are mentioned as potentially predictive of gains in hypertrophy.

ribosome biogenesis

Discussed as being predictive of hypertrophy responses, as ribosomes are cellular machines responsible for building proteins.