Aerobic capacities and exercise tolerance in neuromuscular diseases: A descriptive study




Abstract


Introduction


Up until now, there has been little description of the test exercises carried out in patients with neuromuscular diseases. However, prescription of physical therapy by exercise requires rigorous individualized assessment of the patient’s physical endurance parameters.


Objective


To describe exercise tolerance and external limitation factors in a sample group of adult patients suffering from neuromuscular diseases.


Materials and methods


A descriptive retrospective study of exercise tests realized at the Reims university hospital for patients divided into three groups according to their pathologies: CMT hereditary neuropathies, muscular dystrophies, metabolic myopathies.


Results


Forty-four (44) tests were analyzed. Cessation was occasioned on 63.6% of the cases by muscular symptomatology, with no possibility of maintaining the cycling frequency in 29.5% of the overall population. Insufficient lung volume recruitment was involved in 61.4% of the patients, final oxygen pulse (VO 2 /heart rate) was 80% lower than the theoretical pulse in 50% of the patients, and there existed an early first ventilatory threshold in 54.5% of the cases. Peripheral deconditioning was highly severe in 18% of the population and significantly greater in the subjects suffering from dystrophies (VT1 at 31% of the maximum theoretical O 2 , P < 0.001).


Discussion


The main limitation factor in exercise tests is peripheral. Ventilatory and cardiovascular limitations can nonetheless be added on; while they are absent when the patient is at rest, they are unmasked in effort situations. Exercise tests could be of great interest in screening and managing the relevant pathologies. Multicenter studies on homogeneous populations could facilitate definition of the procedures specific to exercise tests for patients suffuring from neuromuscular diseases.


Résumé


Introduction


Les procédures et résultats des épreuves d’effort réalisées chez des personnes atteintes de maladies neuromusculaires sont peu décrits. Pourtant, la prescription des thérapies physiques par l’exercice nécessite une évaluation rigoureuse et individualisée des paramètres de tolérance aux efforts.


Objectif


Décrire la tolérance et les facteurs limitants aux efforts dans un échantillon de patients adultes atteints de maladie neuromusculaire.


Patients et méthodes


Étude rétrospective descriptive d’épreuves d’exercice musculaire prescrites au CHU de Reims chez des patients classés en trois groupes selon leur pathologie : neuropathies génétiques-CMT, dystrophies musculaires, myopathies métaboliques.


Résultats


Quarante-quatre épreuves sont analysées. L’arrêt est motivé par une symptomatologie musculaire dans 63,6 % des cas, avec une impossibilité de maintien de fréquence de pédalage dans 29,5 % de l’échantillon total. Un défaut de recrutement des volumes pulmonaires intéresse 61,4 % des patients, le pouls d’O 2 final (VO 2 /FC), est inférieur à 80 % de la théorique pour 50 % des patients et il existe un premier seuil ventilatoire précoce dans 54,5 % des cas. Le déconditionnement périphérique était très sévère pour 18 % de l’échantillon et significativement plus important chez les sujets atteints de dystrophies (SV1 à 31 % de la VO 2 maximale théorique, p < 0,001).


Discussion


Le facteur limitant principal d’une épreuve d’exercice est périphérique. Néanmoins, des limitations ventilatoires et cardiovasculaire peuvent s’y associer particulièrement dans les cas de dystrophie musculaire ; absentes au repos, elles sont démasquées à l’effort. L’épreuve d’exercice musculaire pourrait avoir un rôle dans le dépistage et la prise en charge de ces atteintes. La réalisation d’études multicentriques sur des échantillons homogènes permettrait de définir des procédures spécifiques d’épreuves d’exercice.


1


English version


1.1


Introduction


Physical activities have long since been forbidden to patients suffering from neuromuscular diseases. Their prescription has been justified by the perspective of an increased muscle fatigue and the fear of a possible muscle fiber lysis induced by physical activity . This dogma has nonetheless been widely called into question, and several studies have shown the innocuousness, under certain conditions, of suitable techniques aimed at reconditioning to effort .


Exercise tests allow exercise tolerance assessment and help determining not only the relevant limitation factors, but also the parameters helping to individualize retraining and to maximize the benefit/risk ratio of medication by exercise. Even though the means of exercise testing are relatively well-known with regard to cardiovascular and pulmonary diseases or in cases of obesity , they have yet to be described and standardized in the field of neuromuscular pathologies, except for metabolic muscular pathologies .


The main objective of this paper is to describe the capacities of adaptation to effort and to determine the limitation factors in a sample of adult patients suffering from neuromuscular diseases.


1.2


Patients and methods


This is a descriptive retrospective study derived from the exercise tests prescribed by the referral center for neuromuscular diseases at the Reims university hospital. Fifty-three (53) exercise tests were carried out in this population from May 2008 until July 2011.


1.2.1


The population studied


1.2.1.1


Inclusion criteria


The inclusion criteria are as follows:



  • •

    all of the consecutive muscle exercises were carried out in the Reims university hospital from May 2008 until July 2011 with cycle-to-cycle measurement of expired gases in patients suffering from neuromuscular disease. The exercise tests were prescribed by physicians specialized in physical medicine and rehabilitation in order to obtain an evaluation of each patient’s capacity for effort and to subsequently propose a suitable effort retraining program. The patients were ambulatory and considered capable of undergoing muscle exercise testing on a cyclo-ergometer;


  • •

    the patients had to belong to one of the three following pathology-based groups:



    • ∘

      muscular dystrophies: dystrophinopathy, facio-scapulo-humeral (FSH), limb-girdle disease, Steinert myotonic dystrophy, collagenopathy, oculo-pharyngeal dystrophy,


    • ∘

      metabolic myopathies: mitochrondiopathy, glycogenosis, carnitine deficit,


    • ∘

      hereditary peripheral neuropathies: Charcot-Marie-Tooth (CMT) disease.




These criteria have been chosen so as to determine three sub-groups for motor unit diseases dystrophy, myopathy and neuropathy.


1.2.1.2


Non-inclusion criteria


Patients under 18 years of age were not included in this study.


The presence or absence of previous cardiovascular disease did not constitute a criterion of non-inclusion.


1.2.2


Methodology of the exercise tests


1.2.2.1


The test-taking process


All of the exercise tests were carried out by the same experienced physician using an ergocycle (Ergocard, Medisoft) beginning with a no resistance pedalling warm up lasting 1 to 3 minutes and followed with an incrementing resistance adapted to the patient’s functional capacities according to the examiner’s free judgment and ranging from 5 to 20 Watts/minute on ramps or by successive stages. Measurements of respiratory volumes and an ECG at rest were systematically requested prior to the outset of each muscle exercise test.


During the test, electrocardiographic monitoring (12-lead ECG) was carried out. Measurements of heartbeat and blood pressure were noted down once a minute, along with assessment of symptoms (dyspnea, muscle pain, muscle fatigue) according to the Borg scale . The respiratory parameters measured from one cycle to the next with an Ergocard ergospirometer (equipped with a pitot-tube pneumotachograph) were:



  • •

    respiration rate;


  • •

    tidal volume;


  • •

    ventilatory reserve;


  • •

    respiratory equivalents;


  • •

    VO 2 (oxygen flow accepted by the ventilation system, delivered by the blood and used by the organism) and;


  • •

    VCO 2 (carbon dioxide flow rejected by the ventilation system).



1.2.2.2


Maximal exercise criteria


Each muscle exercise test was extracted from the ergospirometer software and subjected to analysis. Different maximal oxygen uptake criteria have been proposed in the literature . We have selected the following criteria:



  • •

    occurrence of a delta VO 2max plateau;


  • •

    respiratory gas exchange ratio (RER) greater than 1.1;


  • •

    chronotropic reserve 15% lower than theoretical maximum heart rate (TMHR) according to the Lange-Andersen formula (210−0.65 × age);


  • •

    exhaustion shown by impossibility of maintaining a pedalling cadence greater than 50 times a minute, even when encouraged, and symptomatology on the Borg scale greater than or equal to 7 out of 10 with regard to myalgia, muscle fatigability and dyspnea.



Three of these criteria must be present in order to consider the test maximal.


1.2.2.3


Determination of the ventilatory thresholds


The first ventilatory threshold was determined according to development of the ventilatory equivalents (more rapid heightening of VE than of VO 2 ) and the Beaver method . The second ventilatory threshold was set following more rapid heightening of VE than of VCO 2 .


1.2.2.4


Exercise tolerance


Exercise tolerance was determined according to the VO 2 level reached , and also according to the maximum theoretical value, with:



  • •

    moderate exercise intolerance when VO 2max represents 60 to 85% of the theoretical value;


  • •

    severe intolerance at rates ranging from 40 to 60%;


  • •

    highly severe intolerance at rates lower than 40%.



This classification is used with regard to pulmonary pathologies, but since it has not been validated with regard to neuromuscular patients, it is given in this study on an indicative basis.


1.2.2.5


The limitation factors considered


In order to determine the nature of the limitation factors, we selected the following criteria :



  • •

    the cardiovascular limitation criteria selected:



    • ∘

      exhaustion of the chronotropic reserve (maximum heart rate greater than 85% of the TMHR according to the Lange-Andersen formula (210−0.65 × age) ),


    • ∘

      HBP > 220/120 mmHg, lowered BP ≥ 10 mmHg,


    • ∘

      final O 2 pulse (VO 2 /HR, reflection of cardiac output according to the Fick equation) lower than 80% of the maximum theoretical O 2 pulse;



  • •

    the respiratory limitation criteria selected:



    • ∘

      exhaustion of the ventilatory reserve (final ventilatory reserve lower than 30%),


    • ∘

      drop in oxygen saturation of more than 4%,


    • ∘

      insufficient tidal volume (TV) elevation (less than 50% of forced vital capacity (FVC),


    • ∘

      Borg score for dyspnea higher than or equal to 7/10;



  • •

    the peripheral limitation criteria:



    • ∘

      early VT1 less than 40% of theoretical VO 2max ,


    • ∘

      myalgia muscle fatigue Borg score higher than or equal to 7/10.




1.2.3


Analysis


The data were analyzed on SPSS software through calculation of number of patients and heart rates with regard to the qualitative variables and through calculation of means with regard to the quantitative variables. Given the low number of patients and in order to limit the constraints inherent to the conditions required for these different statistical tests, the parameters under consideration were compared according to the three aforementioned patient groups through Fisher’s exact test (qualitative variables) and the Kruskal-Wallis tests (quantitative variables). The Least Significant Difference test was considered significant if P < 0.05. We also used Spearman’s rank-order correlation in order to elucidate linkage between the relevant variables.


1.3


Results


1.3.1


General


Forty-four (44) patients suffering from neuromuscular diseases carried out exercise test with a mean duration of 10.8 minutes (extreme values: 5–18 minutes). Nine exercise tests were not included on account of the following pathologies:



  • •

    four unspecified neuromuscular diseases;


  • •

    two type three spinal amyotrophies;


  • •

    one inclusion body myositis;


  • •

    one myofibrillar myopathy and;


  • •

    one periodic familial paralysis.



Patient age differed among the three groups ( P < 0.02). The patients suffering from muscular dystrophies were the youngest.


Only 44 out of the 53 tests had been selected in accordance with the criteria of inclusion and non-inclusion applied with regard to this study. Among the 44 tests, 63.6% were maximal. A first ventilatory threshold had been identified for each one of these tests, and a second threshold for 22 of them.


Maximum aerobic power reached the theoretical value (TMHR), and was measured at an average of 84% for the dystrophic patients and 67% in the cases of metabolic myopathy ( P = 0.06).


The comparative quantitative and qualitative data with regard to the exercise test parameters and to each of the three groups of neuromuscular diseases are given respectively in Tables 1 and 2 .



Table 1

Comparison of the exercise test parameters of the three groups of neuromuscular diseases: qualitative data.








































































































































































































Metabolic % Dystrophies % CMT % Statistics
Sex
M 6 66.7 12 70.6 6 33.3 P = 0.07
F 3 33.3 5 29.4 12 66.7
Maximal
Yes 4 44.4 11 64.7 12 66.7 P = 0.43
No 5 55.6 6 35.3 5 27.8
HRMax
≥ 85% CFMT 1 11.1 3 17.6 5 27.8 P = 0.7
< 85% CFMT 8 88.9 14 82.4 13 72.2
O 2 pulse
≤ 80%th 6 66.7 13 76.5 3 16.7 P < 0.001*
> 80%th 3 33.3 4 23.5 15 83.3
Final Vt
≤ 50%CVF 6 66.7 12 70.6 9 50.0 P = 0.45
> 50%CVF 3 33.3 5 29.4 9 50.0
Ventilatory reserve
≤ 30% 2 22.2 2 11.8 5 27.8 P = 0.5
> 30% 7 77.8 15 88.2 13 72.2
Borg Dyspnea
≥ 7/10 3 33.3 4 23.5 1 5.6 P = 0.14
< 7/10 6 66.7 13 76.5 17 94.4
VO 2 at VT1
< 40% VO 2 MT 5 55.6 15 88.2 4 22.2 P < 0.001*
> 40% VO 2 MT 4 44.4 2 11.8 14 77.8
Borg muscle (fatigability/myalgias)
≥ 7/10 5 55.6 11 64.7 9 50.0 P = 0.68
< 7/10 4 44.4 6 35.3 9 50.0

CMT: Charcot-Marie-Tooth; M: male; F: female; HRMax: maximum heart rate; Final Tv: final tidal volume; VT1: first ventilatory threshold; Borg: designates ratings (out of 10) on the Borg scale. * P ≤ 0.05.


Table 2

Comparison of the exercise test parameters of the three groups of neuromuscular diseases: quantitative data.
























































































CMT Métabolic Dystrophies Statistics
Age (average in years) [minimum; maximum] 49 [33; 69] 49 [28; 66] 35 [21; 65] P < 0.02*
BMI (mean) [minimum; maximum] 25.5 [20.5; 37.4] 27.4 [19.3; 34.5] 24.8 [19.4; 37] P = 0.37
Mean HR at VT1 (beats/minute) 105.6 110.9 109.5 P = 0.49
Mean max HR (beats/minute) 133.61 134.22 137.35 P = 0.93
Mean VT1 power (watts) 50 40 35 P = 0.09
Mean max power (watts) 105 [51; 200] 67 [28; 160] 84 [19; 200] P = 0.06
Mean VO 2 at VT1 (% of VO 2 MT) 50 42 31 P = 0.01*
Mean VO 2max or peak (mL/minute) 1.47 1.22 1.34 P = 0.33
Mean VO 2max or peak (% of VO 2 MT) 74.14 52.78 49.5 P = 0.26
Mean VO 2 /HR (mL/beat) 10.91 13.7 9.54 P = 0.63
Mean VE (L/minute) 60.28 53.1 49.5 P = 0.47
Mean RF (C/minute) 29.3 30.4 33.9 P = 0.65
Mean FVC (L) 4 3.4 3.7 P = 0.17

BMI: body mass index; HR: heart rate, VT1: first ventilatory threshold, HRMAX: maximum heart rate; Max power: maximum power; VO 2max : maximum VO 2 ; VO 2 peak: maximum VO 2 when the test does not meet criteria for maximal uptake; VE: ventilation; RF: respiratory frequency; FVC: functional vital capacity; CMT: Charcot-Marie-Tooth.


1.3.2


Muscular dystrophies


1.3.2.1


Description of the population


Seventeen (17) patients, five women and 12 men, underwent muscle exercise testing. Their average age was 35 years, and their average BMI was 24.8. Among these patients, six had FSH dystrophy, five had Becker’s muscular dystrophy, three had Steinert myotonic dystrophy, one had Bethlem dystrophy, one had limb-girdle dystrophy and one had oculo-pharyngeal dystrophy.


ECG at rest and ventricular ejection function (VEF) at rest were normal; functional respiratory exploration (FRE) showed a restrictive syndrome for two patients and an obstructive syndrome for three patients.


1.3.2.2


Maximum exercise test parameters


Eleven of the 17 tests met the maximal exercise criteria that had been selected.


The most frequent reasons for cessation were impossibility to maintain the pedaling cadence (53%) and muscle pain (myalgias) (41%).


Mean VO 2max was 49.5% of the maximum theoretical value (extreme values: 6–77.4) and maximum mean power was 84 Watts (extreme values: 19–200). Not a single patient reached 85% of the theoretical VO 2max (VO 2 TM), five patients reached more than 60% (moderate exercise intolerance), seven patients more than 40% (severe intolerance) and 5% less than 40% (highly severe intolerance).


1.3.2.3


Cardiovascular parameters


For the tests taken as a whole, the mean maximum heart rate came to 73% of the TMHR. Three patients exhausted their chronotropic reserve, and six reached more than 80% of the TMHR.


O 2 pulse kinetics steadily rose throughout the test, thereby attesting to increased cardiac output accompanying the increments in power. Final O 2 pulse was nonetheless lower than 80% of the theoretical value in 13 cases out of 17. The insufficient rise of the O 2 pulse was not correlated with the non-maximal character of the test ( Table 3 ).



Table 3

Spearman correlations.


































































































































































CRE P VRE P IPO 2 P ITVR P Max P
Total
Maximal 0.234 0.13 0.257 0.097 −0.296 0.054 −0.057 0.717 – –
Obstructive syndrome −0.141 0.366 0.083 0.597 −0.159 0.31 0.29 0.059 0.058 0.71
Restrictive syndrome −0.16 0.458 0.17 0.276 0.244 0.116 0.081 0.606 −0.039 0.804
CMT
Maximal 0.219 0.382 0.219 0.382 −0.055 0.827 −0.124 0.624
Obstructive syndrome −0.189 0.453 −0.189 0.453 −0.239 0.339 0.535 a 0.022 a 0.033 0.896
Metabolic
Maximal – – 0.598 0.089 −0.316 0.407 0.158 0.685 – –
Obstructive syndrome – – −0.189 0.626 −0.5 0.17 0.25 0.516 0.395 0.292
Restrictive syndrome – – 0.357 0.345 0.378 0.316 0.378 0.316 0.06 0.879
Dystrophies
Maximal 0.27 0.295 −0.112 0.668 −0.288 0.263 0.112 0.668 – –
Obstructive syndrome −0.133 0.61 −0.133 0.61 0.27 0.295 0.133 0.61 −0.112 0.668
Restrictive syndrome −0.169 0.517 0.31 0.226 0.019 0.942 −0.3 0.226 0.019 0.942

CRE: cardiac reserve exhaustion; VRE: ventilatory reserve exhaustion; IPO 2 : insufficient oxygen pulse rise; ITVR: insufficient tidal volume recruitment; Max: maximal; CMT: Charcot-Marie-Tooth.

a Significant correlation.



No lowering of systolic blood pressure (SBP) or elevation higher than 220 mmHg was observed.


1.3.2.4


Ventilation parameters


Two patients exhausted their ventilatory reserve.


Tidal volume recruitment was lower than 50% of vital capacity in 12 cases out of 17.


Respiratory frequency at the end of the exercise averaged 34 per minute.


Thirteen out of the 17 patients described dyspnea, and in four cases, it was higher than or equal to 7 out of 10 on the Borg scale.


There was no correlation between insufficient tidal volume recruitment and either maximal testing or the presence or absence at rest of an obstructive or restrictive syndrome.


1.3.2.5


Peripheral parameters


Peripheral symptomatology was represented mainly by:



  • •

    lower limb muscle fatigability in 15 out of the 17 cases and greater than or equal to 7 on the Borg scale in nine cases;


  • •

    myalgias in 13 patients out of 17 with a Borg score higher than or equal to 7 on the Borg scale in five cases.



The first ventilatory threshold occurred at an early stage in 88.2 of the cases.


1.3.3


Metabolic myopathies


1.3.3.1


Description of the population


Six men and three women with metabolic myopathy underwent muscle exercise testing. Their average age was 49 years, and their average BMI was 27.4. Among these patients, four had glycogenosis, four had mitochrondiopathy and one suffered from a carnitine deficit.


ECF at rest and VEF at rest were both normal, and two of the patients had previously registered high blood pressure. FRE showed a restrictive syndrome for two patients and an obstructive syndrome for one patient.


1.3.3.2


Maximum exercise test parameters


Four of the nine tests reached at least three of the maximal exercise criteria that had been selected.


Maximum mean power was 67 Watts and mean VO 2max represented 53% of the theoretical value (extreme values: 28.6–72.8); five tests exceeded 60% (moderate exercise intolerance), one test showed results between 40 and 60% (severe intolerance), and three tests revealed VO 2max lower than 40% (severe intolerance).


Myalgies occasioned cessation in seven out of the nine cases.


1.3.3.3


Cardiovascular parameters


The mean maximum heart rate was 74.8% of the maximum theoretical value (extreme values: 57.6–87.6). In this series, the chronotropic reserve of one patient was exhausted.


Once again, O 2 pulse kinetics steadily rose throughout the test, but with insufficient elevation in six cases out of nine. There existed no correlation with the maximal or non-maximal character of the muscle exercise test, nor was there any anomaly with regard to pressure kinetics.


1.3.3.4


Ventilation parameters


In seven patients, the ventilatory reserve was respected, and insufficient tidal volume recruitment was discovered in six out of the nine cases. There was no correlation between the tidal volume recruitment insufficiency and the presence or absence at rest of an obstructive or restrictive syndrome.


Six patients described dyspnea, and in three cases it was higher than 7 out of 10 on the Borg scale.


Respiratory frequency at the end of the exercise averaged 30 per minute.


1.3.3.5


Peripheral parameters


Eight out of the nine patients complained of myalgias, and five of them described myalgias at the end of the exercise greater than or equal to 7 out of 10 on the Borg scale.


Five of them presented muscle fatigability, which in three cases was greater than or equal to 7 out of 10.


The first ventilatory threshold was reached at an early stage in five of these tests.


1.3.4


Peripheral neuropathies


1.3.4.1


Description of the population


Eighteen patients suffering from CMT disease, six men and 12 women, underwent a muscle exercise test.


Their average age was 49 years, and their average BMI was 25.5.


In all cases, ECG at rest was normal. While no patient had a restrictive syndrome, four patients had an obstructive syndrome.


1.3.4.2


Maximum exercise test parameters


Thirteen out of the 18 tests were maximal.


The main criteria for cessation were impossibility to maintain pedaling cadence (53%) and myalgias (41% of the cases).


Maximum mean power was 105 Watts and VO 2max was 74% of the maximal theoretical value (extreme values: 45–102). In four tests, VO 2max was more than 85% of the theoretical maximum (good exercise tolerance), in 10 cases, it was between 60 and 85% (moderate exercise intolerance) and in four cases between 40 and 60% (severe intolerance).


1.3.4.3


Cardiovascular parameters


The mean maximum heart rate reached 74.6% of the TMHR (extreme values: 56–102). Five out of the 18 patients exhausted their chronotropic reserve.


O 2 pulse kinetics rose constantly throughout the tests, with a terminal value lower than 80% of the theoretical value in three cases out of 18. There existed no correlation with the maximal character of the test, and there was no anomaly involving pressure kinetics.


1.3.4.4


Ventilation parameters


In 13 patients, the ventilatory reserve was respected, and in nine patients the tidal volumes were correctly recruited. Insufficient tidal volume recruitment was correlated with the presence of en obstructive syndrome (0.535, P = 0.022).


Maximal respiratory frequency averaged 29 per minute.


Seventeen patients described dyspnea, which was in one case higher than 7 out of 10.


1.3.4.5


Peripheral parameters


Myalgies occurred on 13 out of the 18 cases, with four patients describing intensity greater than or equal to 7 on the Borg scale.


Seventeen patients complained of muscular fatigability, with eight patients describing intensity greater than or equal to 7.


The first ventilatory threshold was reached at an early stage in four of these tests.


1.4


Discussion


1.4.1


The parameters limiting exercise tolerance


Prescription of muscle exercise testing in patients suffering from neuromuscular disease is possible, accepted and doable. The triangular effort tests carried out averaged 10 minutes of duration, a length of time that is compatible with the clinical state of ambulatory patients. Adaptation to incremented exertion was brought about on a case-by-case basis according to the severity of a patient’s muscle disability and could subsequently be explored and studied over a sufficiently substantial length of time.


More than half of the tests (63.6%) were maximal in terms of the usual criteria. The main reasons for cessation, whatever the pathologies, were myalgies and muscle fatigability. The skeletal muscles may thus be considered as limiting, especially given the fact that in 54.5 of the population studied, occurrence of the first ventilatory threshold (< 40% of VO 2max ) was early.


On this point, there nonetheless exists a statistically significant disparity according to the population under consideration, with an early threshold in 88.2% of the dystrophic patients, 55.6 of the metabolic patients and only 22.2% of the patients suffering from CMT-type neuropathy ( P < 0.001), a finding leading one to suppose that peripheral limitation is more pronounced in muscular dystrophy patients.


And yet, the preponderantly limiting peripheral muscle factor is not the only one helping to explain exercise intolerance in patients with neuromuscular diseases.


Indeed, even though exhaustion of the ventilatory reserve occurred in only 20.5% of the cases included in the study (11.8% of the dystrophies, 27.8% of the CMT and 22.2% of the metabolic pathologies), heightened ventilation takes place mainly at the expense of respiratory frequency, with insufficient tidal volume recruitment in 61.4% of the cases and without either a significant difference between the groups or correlation with the presence at rest of an obstructive or restrictive syndrome. This limitation leads us to think that while it is absent in patients at rest, impairment of the respiratory muscles could be revealed by more intense stimulation during physical exercise. This kind of ventilatory limitation is found in the literature with regard to dystrophic patients or persons suffering from metabolic myopathies . Screening of them is possible through measurement of maximal inspiratory and expiratory pressures and by means of a muscle exercise test objectifying increased maximal ventilation.


Finally, cardiac adaptation cannot be considered altogether normal in the framework of our study. Indeed, even though the heart rate, blood pressure and the O 2 pulse register constant kinetic energy heightening, the final O 2 pulse, which reflects cardiac output, is insufficiently elevated in 16.7% of the CMT cases, 66.7% of the metabolic pathologies and 76.5% of the patients suffering from muscular dystrophies (significant intergroup difference, P < 0.001), that is to say 43.2% of the cases; moreover, it is not correlated with the maximal exercise or oxygen uptake criteria applied in the test. It should be noted that not a single patient in this population had any cardiac pathology diagnosed at rest, and that nor was any ECG at rest or during exercise pathological. Analysis of the O 2 pulse includes its kinetics, which are necessarily on the upswing and also its value, which is a much more questionable criterion . And so, to summarize, while on the one hand the population shows no cardiac pathology at rest and manifests constantly rising kinetics energy, on the other hand, the low peak or maximum value registered in the study generates a question pertaining to the cardio-circulatory limitations on effort revealed by a muscle exercise test: are we dealing here with subclinical cardiac pathology, with central deconditioning?


In this work, the patients with muscular dystrophy are the most limited in their efforts, and associated limitations constitute aggravating factors. For example, the ventilatory limitation (70.6% insufficiency in tidal volume recruitment) found throughout the population participating in the study is associated more frequently than in the two other subgroups with cardiac (76.5% showing insufficiently high O 2 pulse) and peripheral (88.2% with an early threshold) difficulties. However, this interesting finding should be modulated on account of the disparate nature of the pathologies existing in the muscular dystrophy group and, more particularly, the heterogeneity of the types of associated cardiac pathology (rhythm disorder, hypertrophic or dilated cardiomyopathy).


It should also be noted that in the metabolic myopathy group, maximum power figures diverge the most from theoretical values. However, the mean age of the dystrophy patients is significantly lower and may bias the above observation.


1.4.2


Practical applications


Studies on exercise retraining and muscle reinforcement in neuromuscular pathologies have shown only slight alleviation of existing deficiencies and except with regard to their highly positive effects on metabolic diseases (mithochrondiopathies) , they have been disappointing in terms of lessened disability . These mixed or negative results are due to the use of minimally specific scales of functional assessment or quality of life and to inclusion of a small number of participants; as a result and given the state of today’s research, it is difficult if not impossible to draw conclusions. It is nonetheless increasingly apparent that physical activities have beneficial effects with regard to exercise tolerance and to improvement in functional capacities in these types of patients. Supplementary studies are clearly necessary.


Not only in healthy subjects, but also in pathological subjects (coronary, heart failure , arthritic , pulmonary disease ), physical activity allows for improved effort tolerance and functional capacities. The objectivizing of a limitation associated with oxygen transportation in neuromuscular patients renders an exercise retraining indication altogether relevant to their cases. One of the remaining questions pertains to the specific characteristics of suitable physical therapy programs in terms of frequency, intensity, exercise typology, program duration and the overload principle in strength training.


1.4.3


Limitations of the study and perspectives


This work is retrospective. It is meant to encourage further research in its field using a methodology adapted to rare pathologies and by means of a prospective study, if at all possible on a cohort of patients followed in the framework of a multicenter study. This work suffers from obvious selection bias since the exercise tests were carried out at the request of physicians specialized in neuromuscular diseases in the perspective of personalizing their effort retraining prescriptions.


As regards ambulatory patients, the difficulties in adaptation to effort observed in this study will surely be present at a more advanced stage of the disease; given the loss of autonomy entailed, it would nonetheless be wrong to consider the limitations of our study in terms of lessened usefulness.


Moreover, a study specifically devoted to muscular dystrophies with a more homogeneous grouping of pathologies would surely yield more reliable information.


Recommendations for a protocol pertaining to a model muscle exercise test in these patients are particularly complex; after all, the tests in this study were conducted according to subjective personalization criteria. Indeed, they were adapted to the degree of severity of a given patient’s muscle damage, with a less and less rapidly incremented ramp for the severest cases (5 Watts/minute). And in any event, the duration of most of the tests was compatible with the usual recommendations. It is useful to measure the occurrence of muscle fatigue and myalgies during these tests by means of a perception scale such as the Borg scale. At times, it has been observed that the difficulties in access to the technical platform encountered by these patients may exert a negative influence on measurement of exercise tolerance. Research specifically focused on the objective criteria likely to serve as guidelines for individualized exercise tests would be of interest with regard to these patients. And exercise test with other ergometers such as arm ergometers would merit study, as would exercise tests with treadmills or walking tests with portable VO 2 measurement devices.


1.5


Conclusion


Limited exercise tolerance in neuromuscular patients, especially those suffering from muscular dystrophy, is multi-factorial; while a peripheral component is constantly present, cardiac and ventilatory components also need to be taken into account. Performance of an exercise test with these patients facilitates individualization of typologies, intensity and fractionation of the exercises.


The results of this preliminary retrospective study encourage us to further pursue our research in this field so as not only to provide confirmation, but also to propose a protocol for muscle exercise tests adapted to neuromuscular damage and to define the benefits, in terms of adaptation to effort, of the physical activity most suitable for these patients.

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Apr 23, 2017 | Posted by in PHYSICAL MEDICINE & REHABILITATION | Comments Off on Aerobic capacities and exercise tolerance in neuromuscular diseases: A descriptive study

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