Neural adaptations to resistive exercise: mechanisms and recommendations for training practices

Neural adaptations to resistive exercise: mechanisms and recommendations for training practices.

Gabriel DA1, Kamen G, Frost G.

Sports Med. 2006;36(2):133-49.

Abstract

It is generally accepted that neural factors play an important role in muscle strength gains. This article reviews the neural adaptations in strength, with the goal of laying the foundations for practical applications in sports medicine and rehabilitation. An increase in muscular strength without noticeable hypertrophy is the first line of evidence for neural involvement in acquisition of muscular strength. The use of surface electromyographic (SEMG) techniques reveal that strength gains in the early phase of a training regimen are associated with an increase in the amplitude of SEMG activity. This has been interpreted as an increase in neural drive, which denotes the magnitude of efferent neural output from the CNS to active muscle fibres. However, SEMG activity is a global measure of muscle activity. Underlying alterations in SEMG activity are changes in motor unit firing patterns as measured by indwelling (wire or needle) electrodes. Some studies have reported a transient increase in motor unit firing rate. Training-related increases in the rate of tension development have also been linked with an increased probability of doublet firing in individual motor units. A doublet is a very short interspike interval in a motor unit train, and usually occurs at the onset of a muscular contraction. Motor unit synchronisation is another possible mechanism for increases in muscle strength, but has yet to be definitely demonstrated. There are several lines of evidence for central control of training-related adaptation to resistive exercise. Mental practice using imagined contractions has been shown to increase the excitability of the cortical areas involved in movement and motion planning. However, training using imagined contractions is unlikely to be as effective as physical training, and it may be more applicable to rehabilitation. Retention of strength gains after dissipation of physiological effects demonstrates a strong practice effect. Bilateral contractions are associated with lower SEMG and strength compared with unilateral contractions of the same muscle group. SEMG magnitude is lower for eccentric contractions than for concentric contractions. 

However, resistive training can reverse these trends. The last line of evidence presented involves the notion that unilateral resistive exercise of a specific limb will also result in training effects in the unexercised contralateral limb (cross-transfer or cross-education). Peripheral involvement in training-related strength increases is much more uncertain. Changes in the sensory receptors (i.e. Golgi tendon organs) may lead to disinhibition and an increased expression of muscular force. Agonist muscle activity results in limb movement in the desired direction, while antagonist activity opposes that motion. Both decreases and increases in co-activation of the antagonist have been demonstrated. A reduction in antagonist co-activation would allow increased expression of agonist muscle force, while an increase in antagonist co-activation is important for maintaining the integrity of the joint. Thus far, it is not clear what the CNS will optimise: force production or joint integrity. The following recommendations are made by the authors based on the existing literature. Motor learning theory and imagined contractions should be incorporated into strength-training practice. Static contractions at greater muscle lengths will transfer across more joint angles. Submaximal eccentric contractions should be used when there are issues of muscle pain, detraining or limb immobilisation. The reversal of antagonists (antagonist-to-agonist) proprioceptive neuromuscular facilitation contraction pattern would be useful to increase the rate of tension development in older adults, thus serving as an important prophylactic in preventing falls. When evaluating the neural changes induced by strength training using EMG recording, antagonist EMG activity should always be measured and evaluated.

PMID: 16464122 [PubMed - indexed for MEDLINE]

NEMEX-TJR neuromuscular training program

Neuromuscular training seems to gain ground in the therapeutic interventions for almost all the musculoskeletal disorders. It gradually becomes clear to everyone that the neuromuscular adaptations are much more profound and important for our body and its effort to heal itself. Recently, one more study showed the immediate efficacy of neuromuscular exercise in patients with severe osteoarthritis of the hip or knee - See more at Physiospot.

A very nice guideline for the NEMEX-TJR training program presented in this study can be found here.

Spinal cord neurodynamics

A very interesting subject in neurodynamics is the points of convergence of neural tissue. In simple words, these points are the places in the body where two sides of the the neural tissue cord (either in the spinal cord or in the peripheral nerves) come closer to each other. This is happening when the therapist is extending of flexing the limbs or the spine. And this technique is believed that can play a major role in cases of pain due to nerves' compression somewhere along their course.

The following part is a very short part of Chapter 2 summary of “Clinical Neurodynamics” by Michael Shacklock. You can find a short summary of the whole chapter here, or you can buy the book here.

The spinal cord tends to move towards various specific segments. These areas are termed zones of convergence, and these areas include C5-6 and L4-5.  For example, tissues above C5-6 will slide toward this zone, as will tissues below this segment. The midpoint at which tissues diverge is at T6. At this point, tissues below T6 will converge towards L4-5, and tissues above T-6 will converge to C5-6.

Healthy notions of self through neuroscience knowledge

So... what is NOI?

Neuro Orthopaedic Institute (NOI) Australasia has been in operation for 20 years, with highly qualified instructors working on all continents with multidisciplinary audiences. Organising over 100 seminars a year throughout the world, NOI’s faculty members are active in many conferences, university programmes and other postgraduate education sessions. The company reinvests in education and clinically based research and Noigroup Publications has grown from the demand for resources to support this emerging research.

The essence of NOI

Our vision is to seed ‘healthy notions of self through neuroscience knowledge’ worldwide. There are currently five critical conceptual change issues which underpin this: 

Injury or disease does not mean that you feel pain.

The nervous system moves and stretches as we move.

Pain, stress and performance are outputs of the brain.

Knowledge and movement are the greatest pain and stress liberators.

Nervous system plasticity gives new hope and technique.

The biopsychosocial approach, or the merging of the biology of human pain, stress and performance with the psychological and social environment, is the basis of the NOI educational philosophy. It is essentially ‘scientific holism’. Derived mostly from British science, the approach is best typified by Wall and Melzack’s (2005) ‘Textbook of Pain’. 

NOI also espouses strong clinical reasoning strategies, again arising from British critical thinking and later, Australian manual therapy.

Assessment and management of the physical aspects of the nervous system and brain sciences with a focus on neuroplasticity - particularly how the brain represents our body - is an important focus.

Overall, the nervous system is a remarkable, mobile, complex, plastic and changeable organ, and this impacts on both acute and chronic injuries and disease. The NOI education system covers acute and chronic musculoskeletal, central and peripheral, and neuropathic pain states. 

Neural tissue management

We all learn during our education the Upper and Lower Limps Tension Tests. These tests can be used also as mobilization and treatment techniques.

I recently read a few articles on the usefulness and the effect of these and some similar techniques on nerve related pain in the neck and the limps.

Here you can find a great Randomized Control Trial by the School of Health and Rehabilitation Sciences at the University of Queensland, Australia.

Here ypu have fine a novel protocol to develop a prediction model that identifies patients with nerve-related neck and arm pain who benefit from the early introduction of neural tissue management.

Here you can find a very interesting blog entry on neural tissue management.

Finally, here you can find a treatment approach for carpal tunnel syndrome suggested by http://www.handsonemg.com.