Variability in Muscle and Strength Gains After Strength Training in Men and Women
A large-scale study uncovers the complexities of muscle adaptation, revealing notable differences between individual responses to unilateral training.
This study titled "Variability in Muscle Size and Strength Gain After Unilateral Resistance Training" published in Medicine & Science in Sports & Exercise (PMID: 15947721) investigated the differences in muscle size and strength responses to resistance training among a large cohort of men and women.
Study Overview
Objective: To assess variability in muscle size and strength changes following a unilateral resistance training program, focusing on sex differences in these changes.
Participants: The study involved 585 subjects (342 women and 243 men) aged 18 to 40 years, who were tested across eight study centres.
Methodology: Participants underwent 12 weeks of progressive dynamic resistance training targeting the elbow flexors of their nondominant arm. Measurements included:
Isometric strength (maximum voluntary contraction, MVC)
Dynamic strength (one-repetition maximum, 1RM)
Cross-sectional area (CSA) of the biceps brachii using magnetic resonance imaging (MRI).
Key Findings
Variability in Gains:
Muscle size changes varied significantly, ranging from −2% to +59%, with the average increase being around 13.6 cm².
Strength gains also showed wide variability; 1RM strength improvements ranged from 0% to +250%, while MVC changes ranged from −32% to +149%.
Sex Differences:
Men exhibited greater absolute gains in muscle size compared to women (2.5% greater CSA increase).
However, when adjusted for body weight and initial strength levels, women demonstrated relatively higher increases in strength than men.
Statistical Analysis:
Coefficients of variation for changes in CSA were similar between genders, indicating comparable variability.
Significant differences were found in relative strength gains, with women showing greater improvements relative to their baseline strength compared to men.
Conclusions
The study highlights a wide range of individual responses to resistance training, indicating that while some individuals may significantly improve muscle size and strength, others may experience minimal or no gains.
It emphasises that both gender and individual biological factors play crucial roles in determining the extent of muscle adaptation to resistance training.
The findings suggest that while men generally achieve greater absolute muscle size gains, women may benefit more relatively regarding strength improvements.
