Neuromuscular adaptation

Neuromuscular adaptation is a training response in the nervous system that improves force production through greater motor unit recruitment, faster firing and better synchronization.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 14.} Training can also reduce co-contraction, where an opposing muscle works against the prime mover, allowing more force to contribute to strength.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 90.}

Early strength gains are mainly neural: measurable muscle growth takes several weeks, and meaningful protein gain takes a couple of months.^{1Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 14.} Much of this early progress is getting better at the lift, particularly with free weights that demand balance.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 90.} Beyond about 10 weeks, hypertrophy contributes more to strength than neural factors do.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 109.}

In practice

Explain to new clients that fast early gains will slow as progress shifts toward slower mechanisms such as muscle growth.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 46.} Neural factors matter most with loads above 85% of 1RM and with power training.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 109.}

When muscle growth plateaus, variation or progressive overload can bring further neural adaptations.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 109.} Training one limb also raises strength in the untrained limb, by about 8% on average and up to 22%, pointing to a central nervous system effect.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 109.}