What is the predominant factor causing increases in strength during the initial weeks of training?

Changes in whole muscle cross-sectional area reflect hypertrophy, which is a longer-term structural adaptation that becomes the dominant mechanism for strength gains after the initial neural adaptation phase.

Increases in overall limb circumference are an indirect measurement outcome associated with hypertrophy and are not a mechanistic cause of strength improvement.

In the initial weeks of resistance training (approximately the first 4-8 weeks), strength increases are predominantly attributed to neuromuscular adaptations, including improved motor unit recruitment, increased firing rate, and enhanced motor unit synchronization. Structural changes to muscle tissue such as hypertrophy require a longer training stimulus and do not account for early-phase strength gains. This neural adaptation phase explains why strength can increase substantially before any visible change in muscle size.

Increases in muscle-fiber cross-sectional area represent hypertrophy at the cellular level, which is a later-occurring structural adaptation and not the predominant factor in the initial weeks of training.