The walk test can be used to assess aerobic capacity in CMT1A patients

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According to one study, people with Charcot-Marie-Tooth disease type 1A (CMT1A) perform worse on cardiopulmonary stress tests using a stationary bike.

The cardiopulmonary stress test (CPET) is a non-invasive assessment of the cardiopulmonary system at rest and during exercise.

In particular, this poorer performance seemed to be unrelated to cardiopulmonary limitations; rather, it was due to peripheral factors such as muscle atrophy (atrophy).

The results also showed that the 6-minute walk test was a significant predictor of aerobic capacity, one of the parameters of CPET and a measure of an individual’s level of cardiovascular health.

The results of the study suggest that this simple walking test could be used as an indirect measure of aerobic capacity, and therefore cardiopulmonary form, in this patient population, the researchers noted.

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The study, “Cardiopulmonary exercise performance and factors associated with aerobic capacity in neuromuscular diseases, ”Was published in the journal Muscle & Nerve.

The muscle deficits that characterize neuromuscular diseases, such as CMT, often impair movement and contribute to lower levels of physical activity, putting these patients at a higher risk for obesity, cardiovascular and metabolic disorders.

Reduced physical activity can reduce an individual’s aerobic capacity, or VO2peak, which could then “impact the independence of people with neuromuscular diseases,” the researchers wrote. Aerobic capacity is the maximum amount of oxygen absorbed by a person’s lungs during a stress test.

Now, researchers in London, UK have evaluated the performance of 22 adults with CMT1A and 17 adults with inclusion myositis (IBM) during CPET using a stationary exercise bike and sitting down.

CMT1A is the most common type of CMT and IBM is a rare neuromuscular disease characterized by progressive muscle weakness and atrophy associated with inflammation.

The team also assessed whether measures of physical impairment or functional performance could be potential predictors of aerobic capacity in patients with these neuromuscular diseases. Functional predictors can be used to indirectly measure aerobic capacity when the CPET test is not available or indicated in a given patient.

All patients participated in one trial (ISRCTN99826269) who tested the safety and benefits of a three-month sit-on-bike aerobic exercise program.

CPET data was analyzed to determine aerobic capacity, anaerobic threshold, maximum heart rate, ventilatory training (which reflects increased ventilation in response to CO2 production), and the respiratory exchange ratio, an indicator of physical intensity and effort.

The anaerobic threshold is the physiological point during increasing intensity exercise when anaerobic processes, or those that produce energy in the absence of oxygen, become more dominant.

Patient data were compared to those predicted for healthy people of the same age, sex and weight (used as controls) based on published data.

The results showed that CMT1A patients had significantly lower CPET performance for all parameters compared to their respective controls. However, these patients performed better than the IBM group, with significantly higher aerobic capacity, maximum heart rate, and anaerobic threshold.

Further analysis showed that the CMT1A patients had better motor function, walked much faster, and took many more steps per day than the IBM group.

Still, the CMT1A group was younger and had less leg / arm muscle wasting, “which could have influenced the cycling task used for testing,” the researchers wrote.

Notably, while CMT1A and IBM showed high stress levels during CPET, they ended the test with heart rate (about 76% of maximum) and ventilation (about 50% of maximum) reserve, indicating that cardiopulmonary function did not limit exercise.

The results suggest that “peripheral factors, such as muscle atrophy, may have limited performance” in the cycling task, the team wrote.

Additionally, body fat percentage and performance on the 6-minute walk test, which measures distance walked over six minutes, were significant predictors of aerobic capacity in both groups of patients.

The severity of disease in IBM patients, but not in CMT1A patients, was also a good predictor.

Data suggests 6-minute walk test “could be a potential proxy [indirect] measurement of cardiopulmonary form ”in the clinic, the researchers concluded.


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