Neuromuscular Strength in Pulmonary Conditions

           There is no mystical aura that engulfs the gym that gives individuals the gift of brute strength, or gives individual’s cardiovascular capacity like Secretariat, the triple crown record-breaking stallion at Belmont Stakes. There are numerous variables that play an important role in building strength and endurance capacities, but today we are going to focus on the neuromuscular system and how incorporating strength training into one’s routine with pulmonary conditions is very important.

            The human body is always in communication with itself and one communication network is the neuromuscular system. The neuromuscular system is a neural circuit comprised of motor neurons, sensory neurons, and the skeletal fibers at which they are housed and innervated. This system is essential when improving musculoskeletal strength and cardiorespiratory endurance. It also an area that should be considered improving when the goal is to decrease the rate of lung function decline in pulmonary conditions.

            The neuromuscular system provides ongoing communication signals about where the body is in space, what external forces or external loads (weights) are being applied to the muscles and joints, and help to produce the outcome that is desired, whether that is deadlifting, squating, running, walking etc. The amount of communication needed is interdependent on other factors such as intensity, duration, volume, and frequency of training, but there is a benefit in understanding how strength training can improve neuromuscular properties that play an important role in strength, endurance, and cardiorespiratory capacity in pulmonary conditions.    

            In cystic fibrosis (CF), the CFTR gene is an ion channel that regulates chloride. Chloride is a cofactor in the excitability of the nervous system and even though unclear, has been observed to play a role in neuromuscular weakness in CF. The Cystic Fibrosis Transmembrane Regulator (CFTR) expression has been reported in peripheral and central nervous system and facilitates neuronal excitability. In cystic fibrosis (CF), the CFTR expression is altered and this can bring nervous system abnormalities with it. In individuals with COPD, muscle weakness has shown to be associated with corticospinal tract (white matter motor pathway) inhibitions and as such, have been theorized to contribute to muscle weakness.

            Rinke, Artmann, & Stein (2010) observed an important relationship in the CIC-2 channel and neuron excitability within the neuron; a channel that provides membrane regulation in healthy individuals but has been found to not be the case for individuals with cystic fibrosis. Due to the incomplete or non-existent mutation of the CFTR gene in CF individuals, this voltage gate regulator is inefficient causing a change in neuron excitability. The effects of the CFTR gene on the nervous system is still unclear, but there could be a decrease in excitatory potential due to the lack of membrane regulation causing instability in threshold potential. This indirect correlation from a physiological perspective leads one to believe that the nervous system is directly affected by CF.

            The neuromuscular system is a highly adaptable system that when stressed (e.g., use of heavy loads) can increase neural drive properties to the area that is being targeted during training. This impact is so powerful that contralateral (opposite side) and surrounding musculoskeletal regions will benefit from heavy resistance training. For example, doing bicep curls on one arm will transfer over added benefits to the other arm. This has been shown during rehabilitation programs where a person has an arm in the sling and only can work the opposite arm, but when testing the arm that was in the sling it had also improved strength. In addition, this can be seen when a person learns a new lift and in the first month of training he/she can see a dramatic increase in weight until they hit a plateau. This is due to the neuromuscular system updating and improving the communication and processing system in the muscles that the person is training.

            So, what does this all mean for you? That the neuromuscular system plays an important role in increasing muscular strength by improving the motor unit recruitment. Furthermore, muscular neural adaptations have shown to play a greater role in muscular strength than muscle hypertrophy (increased muscle fiber size). This is something important to understand when training individuals with pulmonary conditions due to the longitudinal decline of muscle weakness and exercise tolerance. It is important to implement exercises in a manner that encourages neuromuscular growth.

Neuromuscular Strength Training Tips

            Start integrating 2-3 days a week of strength training of loads (weight) greater than ≥70% of your 1-rep max. The National Strength and Conditioning Associations has a Training Load Chart that can help guide you when trying to decide on how much weight you should be lifting at loads 70% and greater. What is cool about this chart is it gives you guidelines on what weight to use and for how many reps depending on the percentage you want to train at. For example, if you bench press 220lbs for 1 rep, you would take 220 and times it by .7 (70%) and you would get 154lbs. On the chart, if you scroll down to the 1-rep max until you reach 220lbs, then shift your gaze to the right until you reach the 70% column and 154lbs appears as your starting weight for 70%. Above the 70% there will be the total amount of reps that is recommended at that weight. Now, this training load chart is a general template and these numbers will not be exact for everyone. There will be some differences either above or below the number suggested, but this chart allows you to get an idea on where to start.

            We can’t paint neuromuscular training improvements in pulmonary conditions with a broad brush, but strength training ≥70% does improve neuromuscular strength and can directly help improve cardiorespiratory endurance when supplementing it with an aerobic or anaerobic based conditioning program. Improving absolute and submaximal strength is an important factor in the contribution to fighting pulmonary conditions. Improving neural excitability in skeletal muscle can aid in reducing muscle weakness and improve exercise capacity tolerance. However, to see a continuous linear gain in muscle strength, the loads being lifted must also increase and at some point, increase past 60% of an individual’s 1-rep max. Last but not least, and just as important, keep the quality of movement high. As the weight is increased, so will the demand for movement quality. It is better to do perform less reps with a higher quality of movement then to perform more reps with poor quality. Always think quality over quantity when it comes to strength training.

References

Alexandre, F., Héraud, N., Tremey, E. et al. (2020). Specific motor cortex hypoexcitability and hypoactivation in COPD patients with peripheral muscle weakness. BMC Pulmonary    Medicine, 20(1),

National Strength and Conditioning Association. (2012). Training Load Chart.             https://www.nsca.com/contentassets/61d813865e264c6e852cadfe247eae52/nsca_training _load_chart.pdf

Rinke, I., Artmann, J., & Stein, V. (2010). ClC-2 voltage-gated channels constitute part of the background conductance and assist chloride extrusion. The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, 30(13), 4776–4786.

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