Integration of neural activation and fiber hypertrophy

Integration of neural activation and fiber hypertrophy

Research on resistance training adaptations indicates that early increases in voluntary strength, or maximal force production, are associated primarily with neural adaptations resulting in increased voluntary activation of muscle. This was clearly demonstrated in a study of both men and women who participated in an eight-week, high-intensity resistance training program, training twice per week. Muscle biopsies were obtained at the beginning of the study and every two weeks during the training period. Strength, measured according to the 1RM, increased substantially over the eight weeks of training, with the greatest gains coming after the second week. Muscle biopsies, however, revealed only small, statistically insignificant increases in muscle fiber cross-sectional area by the end of the eight weeks of training. Thus, the strength gains were largely the result of increased neural activation.

Long-term increases in strength generally are associated with hypertrophy of trained muscle. It takes time to build protein through a decrease in protein degradation, an increase in protein synthesis, or both. Notable exceptions to this generalization have been found. A six-month study of strength-trained athletes showed that neural activation explained most of the strength gains during the most intensive training months and that hypertrophy was not a major factor. It appears that neural factors make their greatest contribution during the first 8 to 10 weeks of training. Hypertrophy contributes little during the initial weeks of training but progressively increases its contribution, becoming the major contributor after 10 weeks of training.