Myotonic Dystrophy 1 (DM1) causes progressive myopathy of extremity muscles. DM1 may also affect muscles of the trunk. The aim of this study was to investigate fat infiltration and muscle size in trunk muscles in DM1 patients, and in an age and gender matched control group. Further, explore how fat infiltration and degree of atrophy in these muscles are associated with motor and respiratory function in DM1 patients.
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Trunk muscles in DM1 patients had significant higher levels of fat infiltration and reduced muscle size compared to age and gender matched controls. In DM1 patients, fat infiltration was associated with reduced muscle strength, mobility, balance and lung function, while muscle size was associated with reduced muscle strength and lung function. These findings are of importance for clinical management of the disease and could be useful additional outcome measures in future intervention studies.
We recently documented early and severe impairment in trunk muscles when measured with manual muscle strength tests (MMT) [7]. The trunk impairment was correlated to lower general mobility, reduced balance and use of Bilevel Positive Airway Pressure (BiPAP). The severity of the impairments and their correlation to the size of the CTG expansion suggested that DM1 could cause myopathy in trunk muscles [7]. There is a need for more knowledge about trunk muscle impairment in DM1 and how trunk muscle weakening may influence function [8]. Falls are prevalent in DM1 patients, and knowledge of whether myopathy in trunk muscles are related to mobility or balance, is of clinical importance [9]. Respiratory function may also be impaired [3, 10], and represents the main cause of mortality in the group [11]. The abdominal muscles are important for respiratory function [12] and involvement of trunk muscles may therefore indicate a need for ventilatory support [7].
Fat infiltration of muscles has been studied in healthy subjects and is related to age, gender and BMI [19, 20]. These variables are therefore to consider when interpreting MRI findings in DM1 patients. No previous MRI study of trunk muscles in DM1 has compared patients with healthy controls. The aim of this study was to investigate muscle size (diameter and area) and fat infiltration in trunk muscles in DM1 patients, and compare the results to an age and gender matched control group. In the DM1 patients we also aimed to explore whether the amount of fat and the size of the trunk muscles correlate to trunk muscle strength, respiratory function and other motor measurements.
To our knowledge, this is the first study of fat infiltration and muscle size in trunk muscles in DM1 patients comparing cases and healthy controls. It is also the first study of trunk muscle involvement measured by MRI in relation to results from clinical testing of strength and other muscle function tests as well as respiratory variables. We found a statistically significant difference in fat infiltration and muscle size between patients and age-matched healthy controls. In addition, we have shown that there are strong relations between MRI findings in the patient group and impairment of both motor performance and respiratory function.
We find a high and significant correlation between the sum score of muscle size in the trunk flexors and FVC. We think that this finding reflects the importance of the rectus abdominis in forceful expiration [12]. There was also a significant correlation between the sum score of fat infiltration in the trunk flexors and FVC, which is contrary to a previous study [16]. However, muscle size was the most correlated to FVC, and this finding is in line with muscle volume as the most predictive value of strength function [17]. Trunk muscles in DM1 may clearly be fat infiltrated and atrophied, both myopathic changes related to muscle strength and FVC, and should not be neglected in this patient group. Rather, since respiratory function has impact on life expectancy, we suggest that trunk muscle strength should be thoroughly assessed in the clinical follow up of these patients.
Fat infiltration in the trunk flexors is correlated to performance on TUG. Stabilization, flexion and rotation of the trunk are involved in TUG and therefore all abdominal muscles are involved in this task. These findings are of importance in the understanding of how balance may be influenced by trunk impairments in the DM1 group and support our previous finding of a relation between strength in trunk muscles and TUG [7]. Bachasson et al. found that the postural stability and gait in DM1 patients was disturbed and related to strength in the distal part of the lower extremities. The authors also argue that changes in pelvic tilt may play a role in gait disturbances in the DM1 group. However, this study did not investigate the trunk muscles [38] . Our findings suggest trunk muscles should be included when postural stability or balance is investigated in the DM1 group. In patients with facioscapulohumoral muscular dystrophy (FSHD) gait function has been shown to be more related to fat infiltration in the trunk muscles than to fat infiltration in the lower extremities [39]. Interestingly, RMI, the measure of general mobility, was significantly related to both fat and size in the abdominal and the back muscles in our patients. This finding is understandable as this test is composed of gross motor movements, some that are dependent on all trunk muscles working against gravity, which demands strength levels above grade 2 (muscle strength score indicating ability to move the body part against gravity). Since RMI involve all trunk muscles, it is possibly more sensitive to change and seems to be able to predict myopathy in trunk muscles. However, which strategy a subject uses, when performing the different tasks of RMI is not fixed and allows for compensation such as using the arms to get from a supine to a sitting position. An accurate observation of how the tasks in the RMI are performed by DM1 patients would be of interest, since this may indicate trunk function impairment.
The correlation between fat infiltration in the trunk flexors and trunk extension may be explained by the opposing role the trunk flexors have to trunk extensors and the need for co-contraction of antagonists in stabilizing the spine [41, 42]. A lack of correlation between trunk extension strength and fat infiltration in the trunk extensors, may be due to the higher frequency of fat infiltration present in the cranial parts, which were not included in this study, and to a greater demand of power from this part of the erector spinae in the trunk extension test performed [43]. The only significant correlation of muscle size and strength was between the trunk flexors and trunk flexion strength, measured by the curl up, a result in line with muscle volume as the most predictive value of strength function [17]. Compensation from other muscles may be the reason for the lack of relations between muscle size and trunk extension. Only the lumbar part of the erector spinae was included in this MRI study, and both the thoracic parts of the erector spinae as well as cervical extensors and other trunk extensors are known to contribute in trunk extension [44].
CTG expansion size was not significantly correlated with any MRI measure; nor fat infiltration or muscle size, in neither trunk flexors or trunk extensors. This result may be due to the mosaic expression of CTG repeats in different tissues in DM1 patients; a higher number of CTG repeats are found in skeletal muscles compared to blood [45]. A significant correlation between MRI measured fat infiltration in trunk flexors and CTG repeats measured in blood is documented by Park. However, in the same study a correlation between fat infiltration in trunk extensors was not significant [16]. This finding may be taken into account when standards of care are recommended. Health professionals should be aware that decreased respiratory function probably might develop early and independent of CTG size.
The presence of fat infiltration and atrophy in trunk muscles in patients with DM1 shows that these muscles are affected by DM1 myopathy. Fat infiltration was correlated with reduced balance, and both fat infiltration and increased atrophy was correlated with reduced respiratory function. These findings are of importance for clinical management of the disease and could be useful as an additional outcome measure in future intervention studies.
Evaluating the scientific merit of articles and advertisements about exercise and nutrition products is a key skill that all sports nutrition professionals must possess. To assist members and other advocates of the International Society of Sports Nutrition (ISSN) in keeping up to date about the latest findings in sports nutrition, the ISSN Exercise & Sports Nutrition Review: Research & Recommendations has been updated. The initial version of this paper was the first publication used to help launch the Journal of the International Society of Sports Nutrition (JISSN, originally called the Sports Nutrition Review Journal). This paper provides a definition of ergogenic aids and dietary supplements and discusses how dietary supplements are legally regulated. Other sections highlight how to evaluate the scientific merit of nutritional supplements and provide general nutritional strategies to optimize performance and enhance recovery. Finally, a brief overview of the efficacy surrounding many supplements commonly touted to promote skeletal muscle hypertrophy and improve physical performance is provided. Based upon the available scientific literature testing the efficacy and safety of the nutritional supplements discussed herein, all nutritional supplements discussed in this paper have been placed into three categories based upon the quality and quantity of scientific support available:
ATP is the primary intracellular energy source and in addition, has extensive extracellular functions including the increase in skeletal muscle calcium permeability and vasodilation. While intravenous administration of ATP is bioavailable [240], several studies have shown that oral ATP is not systematically bioavailable [241]. However, chronic supplementation with ATP increases the capacity to synthesize ATP within the erythrocytes without increasing resting concentrations in the plasma, thereby minimizing exercise-induced drops in ATP levels [242]. Oral ATP supplementation has demonstrated initial ergogenic properties, after a single dose, improving total weight lifted and total number of repetitions [243]. ATP may increase blood flow to the exercising muscle [244] and may reduce fatigue and increase peak power output during later bouts of repeated bouts exercise [242]. ATP may also support greater recovery and lean mass maintenance under high volume training [245], however, this has only been reported in one previous study. In addition, ATP supplementation in clinical populations has been shown to improve strength, reduce pain after knee surgery, and reduce the length of the hospital stay [246]. However, given the limited number of human studies of ATP on increasing exercise-induced gains in muscle mass, more chronic human training studies are warranted. 2ff7e9595c
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