Neural Adaptation

The concept of neural adaptation is fundamentally important knowledge that helps us understand the process by which the Weightlifter develops skill, power, strength, speed and coordination. For example, the concept helps the Weightlifting coach to understand why:

  • An increase in strength is initially achieved without any measurable increase in muscle hypertrophy
  • Beginners display inhibition and awkwardness of movement in the initial stages of learning Weightlifting skill
  • The training of Weightlifters must be predominantly high in intensity i.e. over 80%.
  • Athletes with extensive experience in weight-training often have significant difficulties in learning Weightlifting movements
  • Resistance training to develop greater strength within a muscle group will simultaneously develop strength within muscles that oppose the contraction of the trained muscle group.
  • Ex-athletes retain the ability to lift far more than untrained or novice individuals long after they have ceased training.

The Motor Unit

Motor Unit
Figure 2: A Motor Unit: A motor unit is made up of a motor neuron and the skeletal muscle fibres innervated by that motor neuron.

When an individual begins Weightlifting, strength is gained rapidly without any measurable hypertrophy of muscle tissue. This is evidence that the development of muscular strength is a function not only of adaptation within muscle tissue itself but also the nervous system that innervates muscles to contract (Gabriel, Kamen & Frost, 2006). This adaptation of the nervous system is referred to as neural adaptation and includes several possible mechanisms that contribute to strength development. In order to understand these mechanisms, it is beneficial to have a basic knowledge of the structure known as the ‘motor unit’ (See Figure 2). A motor unit consists of a motor nerve cell (motor neuron) situated in the spinal column, the motor nerve fibre, the motor end-plate or junction between the nerve fibre and the muscle, and the colony of muscle fibres innervated by the motor neuron (Reilly, Secher, Snell, & Williams, 1990). A motor unit is thought to have a specific threshold for stimulation. If the electrical signal from the motor neuron via the nerve fibre is sufficiently strong (greater than the threshold) all muscle fibres which are part of the motor unit will contract. If a pulse is received that is less than the threshold, then the motor unit will not be ‘fired’, i.e. there will be no contraction by any muscle fibre in the motor unit. This is often referred to as the all or none principle (all muscle fibres in the motor unit will fire or none will).

 The strength of a muscle contraction will in part be determined by a combination of any or all of the following:

  • The total number of motor units which can be activated (fired) at any one time
  • The frequency of electrical stimulation pulses received by the motor unit
  • The synchronisation of motor unit firing
  • Greater efficiency at the neuromuscular junction (motor end plate)
  • Neuroplasticity or enhancement of the motor cortex area of the brain
  • Possible reduced inhibition of agonist muscle contraction (unconfirmed by research)

For a more in depth understanding of these factors read Neural Adaptation by Gabriel, Kamen and Frost (2006).

For the Weightlifting coach a detailed knowledge of these mechanisms is not necessary. Instead, it is more important to consider the overall importance of neural adaptation to the improvement of athletic performance. The development of strength is much more complex than mere hypertrophy and it is useful to discuss how an understanding of the concept of neural adaptation helps the coach to optimise the training of the Weightlifter.

Neuroplasticity

Traditionally in Weightlifting, much of our thinking about training focusses on the observable physical changes that take place within the musculature when in reality the most profound changes take place within the nervous system. In particular, in recent decades science and medicine have made great advances in understanding ‘Neuroplasticity’ and how the brain adapts to stimuli within the environment. Learning the movement patterns of Weightlifting presents very strong stimuli that cause adaptation in the brain and nervous system. The problem for the brain, particularly when learning a new movement that is complex and involves high intensity muscular contraction, is to activate (or not activate) motor units within muscle groups to cause and control very precise movement of the body.  In performing the complex skills of Weightlifting, flexion and extension within multiple joints must be coordinated, and the resultant movement must fall with a tolerance range that allows the achievement of the lift. In Weightlifting, the contractile force developed by muscle tissue is well beyond the norm for everyday life and therefore part of the brain’s adaptation is not only to precisely coordinate movement within multiple joints but also to stimulate muscle tissue to contract more forcibly than previously experienced.

Training Intensity

The training of the Weightlifter must take account of the need for neural adaptation that enables the athlete to acquire the ability to produce rapid and forceful contraction of muscle tissue in a highly sophisticated and coordinated way. Since now, we have some understanding that strength is not purely a matter of muscle size but relies heavily on neural adaptation and the excitation of motor units, it is important to ask questions about the specific type of training needed for Weightlifting.

Since the 1970’s, the authors of Weightlifting texts have put forward the notion that strength training is best engendered by training 5-6 reps per set to promote hypertrophy.

The advanced lifter and in particular those striving to increase muscle mass, lift the bar 5-6 times in a set. A great number of repetitions of an exercise during one set is used for providing the excessive load for one and the same group of muscles to evoke stress reaction and obtain the strength increase (Falameev, n.d.).

On the basis of a training analysis of top USSR lifters, we conclude that lifters whose bodyweight is at the top (or even above) of their weight class should, as a rule, use sets of 2-3 reps. But since strength training is more effective if growth of structural protein occurs, we advocate episodic use of 4-6 rep sets as being most favourable for muscle trophicity (Vorobiev, 1978).

Both Falameev and Vorobiev were distinguished Russian athletes who went on to become coaches during the years when the USSR was dominant in world Weightlifting.

The relationship between strength and cross-sectional area of muscle is well understood (Fukunaga et al, 2001) thus training for hypertrophy is an important objective. However, at best an athlete can achieve 80-85% of 1RM by performing sets of 5-6 reps and although the effort of the individual is intense, it is arguable that a different form of neural adaptation is required for performance improvement in Weightlifting.

A different approach to performance improvement in Weightlifting was taken by Ivan Abadjiev, head coach of the Bulgarian Weightlifting team, that astonished the world of Weightlifting in the 1970’s.  The approach relied on single rep sets up to planned or expected maximum efforts on a daily basis not only the classical movements of the snatch and the clean & jerk but also squats (Garhammer & Takano, p511). In more recent times, Sivokhin and colleagues (2012) stated no more than 1-2 repetitions per set were used in the training of the Kazahkstan Weighlifting Team in pursuit of the goal of selective hypertrophy of fast twitch muscle fibres. Support for this approach is based on the need for a sufficiently high training load to maximally recruit muscle fibres and produce the required neural adaptation (Hakkinen, 1985; Gonzalez-Badillo, Izquierdo & Gorostiaga, 2006). Furthermore, in Australia, Jones and Keelan (2005) recommend that strength training is advanced by training 1-2 reps per set at very high intensity (90-100+%) and at such a level of intensity, it is not possible to achieve 5-6 reps per set.

In the Weightlifting world there is much uncertainty about the best methodology to develop strength. It is still commonplace to see athletes pursuing strength development with high volume training utilising 5-6 reps per set particularly during the ‘preparatory phase’ of a periodised training program. Certainly athletes do gain in hypertrophy and advance their 5RM result of such training but a reliance on 5-6 reps per set for strength training in the lead up to an important competition is not congruent with neural adaptation theory. The lifting of maximal or near-maximal weights (high intensity training) is fundamentally necessary to stimulate the required neural adaptation. Maximising strength, power and hypertrophy may only be accomplished when the maximal numbers of motor units are recruited. Thus heavy loading in experienced individuals is needed to recruit high-threshold motor units that may not be activated during light to moderate lifting (Kraemer & Ratmess, 2004).

However, there is strong support for the notion that high-intensity (90%+) training with low rep sets (1-2) cannot be performed all year round. Among the negative influences of an over focus on 1 or 2 heavy or maximal efforts per set is a risk of encountering a training plateau (Kraemer & Ratmess, 2004), and a worsening of technique and emotional state (Orlov, 2015).  For these reasons, a typical Weightlifting program takes a periodised approach that includes a preparatory phase and a competition phase. The preparatory phase provides some relief from continual high-intensity effort but during this phase athletes can still be challenged by pursuing personal bests for higher repetition sets for strength training.

In typical high-volume (preparatory) phases for weightlifters contain more training sessions per week (6-15), more exercises per session (3-6) and more repetitions per set (4-6).Typical high-intensity (competition) phases for Weightlifters contain fewer training sessions per week (5-12), fewer sets per exercise (3-5), and fewer repetitions per set (1-3) (Garhammer & Takano, p508).

Inhibition of Movement

Neural adaptation also helps us to understand the transformation of beginners in Weightlifting. Initially movements of the beginner appear inhibited, restricted and uncoordinated and, in general, we attribute this to lack of skill. However, this inhibition of movement can also be explained as a mechanism to prevent injury, or more especially to protect joint integrity (Gabriel, Kamen & Frost, 2006). When a motor task is unfamiliar, the central nervous system has to deal with the need not only to produce force through muscle contraction but also to limit the force produced as a measure of self-preservation. Logically, for the beginner, self-preservation is a higher order need than maximal performance and the inhibition of movement begins to dissipate only after considerable skill learning and neural adaptation.

The question of whether neural adaptation through strength training also involves a reduction in antagonist action has been investigated. As has been discussed in pages 8-9, when a muscle contracts to cause movement there is also a co-activation in the antagonist muscle. Thus, the force produced in an agonist muscle must not only overcome the weight to be lifted but also the opposing force developed in the antagonist muscles. A study by Carolan and Cafarelli (1992) found a 11.5 – 14.9% reduction in Biceps Femoris (BF) activity as a result of isometric training of knee extensor muscles. The BF activity was measured using a non-invasive technique in which electrodes are placed on the skin overlying a muscle to detect the electrical activity of the muscle (MedicineNet.com, 2015). However a study by Gabriel and Kroll (1991) contradicts the notion that the training process reduces antagonist muscle activity. In their study, Gabriel and Kroll found that however people engage in strength training there is an increase in antagonist activity. So, according to this finding, no matter how much your quadriceps develop in strength as a result of performing squats, there would be an increase in antagonist action of the hamstrings even when performing maximal attempts. To some extent this is logical, but the Gabriel and Kroll study does not rule out that there is a beneficial change in the ratio of agonist to antagonist activity.

The inhibition of movement as a result of the co-activation of antagonists may not seem knowledge that is overtly useful to the Weightlifting coach. However, such knowledge may explain some common technical issues and lead to the development of remedial strategies. As an example, athletes who move into weightlifting after extensive training of the biceps generally have difficulty in attaining and maintaining a strong lockout in the jerk. In such a circumstance, the biceps are co-activated as the triceps perform the work to extend and lockout the arm at the elbow joint. When the biceps have been well-developed, their opposing force to the extension of the elbow by the triceps is very strong. It takes time and persistence to detrain the biceps and retrain the musculature of the arm and shoulders to attain the coordination and balance of forces required to sustain a good lockout. This situation is made worse when athletes have also engaged in extensive bench press training, as this also creates strong antagonist action from the pectoral muscles. As stated on page 10 (Figure 1), co-activation of the hamstrings during the pull or the squat creates force that opposes the work performed  by the quadriceps.

Neural adaptation is therefore a topic of importance to the weightlifting coach which helps to better understand training methodology and deal with common technical issues.  An insight into neural adaptation enables a better understanding of strength, skill learning, muscle fibre recruitment, muscle fibre transformation, training intensity, technical issues, co-activation and inhibition of movement. How we perform in sport is very much about the ‘intelligence’ we can create within our nervous system rather than a genetic pre-disposition of muscle fibres as many believe.

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