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Physiology of Strength Training

This is an excerpt from Periodization of Strength Training for Sports-4th Edition by Tudor O. Bompa & Carlo Buzzichelli.

Until a few years ago, we believed that strength was determined mainly by the muscles’ cross-sectional area (CSA). For this reason, weight training was used to increase “engine size”—in other words, to produce muscular hypertrophy. Now, we see it differently. CSA remains the single best predicting factor of an individual’s strength, but the main factors responsible for strength increase (especially in advanced athletes) are in fact the neural adaptations to strength training, such as improvements in inter- and intramuscular coordination and the disinhibition of inhibitory mechanisms (refer back to chapter 2 for further explanation on the neural adaptations to strength training).

Briefly, an athlete’s ability to generate high forces depends to a great extent on the following factors.

• Intermuscular coordination: the ability to synchronize all muscles of a kinetic chain involved in an action
• Intramuscular coordination: the capacity to voluntarily recruit as many motor units as possible and send nerve impulses at high frequencies
• Hypertrophy: the diameter or cross-sectional area of the muscle involved

Improving intermuscular coordination—coordination between muscle groups—depends strictly on learning (technique), which requires many reps of the same exercise using a moderate load (40%-80% percent of 1RM) and performed dynamically with perfect technique (MxS-I). Intramuscular coordination—the capacity to recruit fast-twitch muscle fibers—depends on training content, in which high loads (80%-90% of 1RM) are moved explosively (MxS-II). Both types of strength training, MxS-I and MxS-II, activate the powerful fast-twitch motor units.

Overall muscle mass depends on the duration of the hypertrophy phase, but an athlete does not necessarily have to develop large muscles and high body weight to become significantly stronger. Throughout maximum strength and power training, athletes learn to better coordinate the relevant muscle groups and use loads that result in higher recruitment of fast-twitch muscle fiber (loads greater than 80% of 1RM). By using the methods outlined in this chapter for the maximum strength phase, athletes can improve their maximum strength with some gains in functional muscle mass.

Of the three types of muscle contraction, eccentric contractions create the highest tension (up to 140% of concentric 1RM strength). The second-highest tension is created by isometric contractions (up to 120% of concentric 1RM strength). Still, concentric strength must be developed at the highest levels because most sport actions are concentric. Indeed, the direct application of other forms of contraction—isometric and especially eccentric—directly benefits athletic performance by supporting further improvements in concentric force.

Exercises used to develop maximum strength should never be performed under conditions of exhaustion, as they are in bodybuilding, except when the goal is to achieve absolute strength gains (strength plus hypertrophy). Because MxS training engages maximum activation of the central nervous system—including factors such as concentration and motivation—it improves intermuscular and intramuscular coordination. High CNS adaptation (e.g., improvement of neuromuscular coordination) also results in adequate inhibition of the antagonist muscles. This means that when maximum force is applied, these muscles are coordinated in such a way that the antagonists do not contract to oppose the movement.

The CNS normally prevents the activation of all the motor units available for contraction. Eliminating this inhibition is one of the main objectives of MxS-II training—that is, intramuscular coordination training with loads above 80% of 1RM. This reduction in CNS inhibition is accompanied by an increase in strength that results in the greatest improvement in specific performance potential.

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