Pectoralis major and triceps brachii cross-sectional area measured on different planes: the effect on the muscle size-strength relationship.

BACKGROUND: Magnetic resonance imaging (MRI) is a well-used technique to assess muscle size and can be acquired on different planes. Pectoralis major (PM) and triceps brachii (TB) muscles are often acquired and analyzed on the axial plane, however it is unknown if anatomical cross-sectional area (CSA) calculated from different planes will affect the muscle size-strength relationship. Thus, the first aim of the present study was to identify if the CSA of the PM and TB measured on different planes presents a similar muscle size-strength relationship. A secondary aim was to investigate if the quantification of CSA of the PM and TB muscles are similar between sagittal and axial plane. METHODS: Fifteen males underwent an MRI examination, and after that, one-repetition maximum (1RM) test was performed. RESULTS: There was a significant relationship between 1RM and PM CSA measured on the axial and sagittal plane (r≤0.81), while the relationship with TB CSA was only good on the axial plane (r=0.65) and not significant on the sagittal plane (r=0.27). ICC between planes was excellent for PM CSA (0.96) with Bland-Altman procedure showing agreement between planes (d=0.376; P=0.612). Contrarily, TB CSA ICC was week (0.07), with Bland-Altman procedure showing no agreement between planes (d=-24.49; P=0.022). CONCLUSIONS: CSA measured at axial plane from PM and TB muscles showed a significant relationship with 1RM, while only PM CSA on the sagittal plane showed a significant relationship with 1RM. Finally, it was demonstrated that PM images showed a great reliability between planes, which was not true for TB muscle.

Muscle volume vs. anatomical cross-sectional area: Different muscle assessment does not affect the muscle size-strength relationship.

Muscle volume (MV) and anatomical cross-sectional area (CSA) are used as measures of muscle-size, but determining these from magnetic resonance imaging (MRI) is a very time-consuming process. Additionally, it is unclear if the use of different muscle size assessments (all vs. reduced number of slices images) would impact the muscle size-strength relationship. Thus, this study aimed to investigate if muscle size calculation by using a reduced or all slices images from pectoralis major (PM) would maintain a similar muscle size-strength relationship with bilateral maximal dynamic and isometric contractions on a bench press exercise. Twenty-four healthy males underwent an MRI examination to measure PM muscle size, and maximal isometric and dynamic contractions (by one repetition maximum, 1RM) were performed. Correlations between maximal isometric voluntary force (MVF) and dynamic strength (1RM) with muscle size variables [three images from the largest part of PM (CSA3MAX), three images accounting for the shape -first image, middle image, final image- of the PM (CSA3), and MV] were performed. The correlation between 1RM with MV, CSA3, and CSA3MAX were 0.84, 0.832, and 0.727 (p < 0.001), respectively. The correlation between MVF with MV, CSA3, and CSA3MAX were 0.738, 0.733, and 0.604 (p < 0.001), respectively. Overall, PM MV and CSA3 exhibit a stronger and similar muscle size-strength relationship during maximal dynamic and isometric tests than CSA3MAX. Therefore, a reduced number of slices (CSA3) could be used as an alternative to considerably reduce the time of analysis without compromise muscle size-strength relationship.

Ecto-nucleotidase activities of promastigotes from Leishmania (Viannia) braziliensis relates to parasite infectivity and disease clinical outcome.

BACKGROUND: Leishmania (Viannia) braziliensis has been associated with a broad range of clinical manifestations ranging from a simple cutaneous ulcer to destructive mucosal lesions. Factors leading to this diversity of clinical presentations are not clear, but parasite factors have lately been recognized as important in determining disease progression. Given the fact that the activity of ecto-nucleotidases correlates with parasitism and the development of infection, we evaluated the activity of these enzymes in promastigotes from 23 L. braziliensis isolates as a possible parasite-related factor that could influence the clinical outcome of the disease. METHODOLOGY/PRINCIPAL FINDINGS: Our results show that the isolates differ in their ability to hydrolyze adenine nucleotides. Furthermore, we observed a positive correlation between the time for peak of lesion development in C57BL/6J mice and enzymatic activity and clinical manifestation of the isolate. In addition, we found that L. (V.) braziliensis isolates obtained from mucosal lesions hydrolyze higher amounts of adenine nucleotides than isolates obtained from skin lesions. One isolate with high (PPS6m) and another with low (SSF) ecto-nucleotidase activity were chosen for further studies. Mice inoculated with PPS6m show delayed lesion development and present larger parasite loads than animals inoculated with the SSF isolate. In addition, PPS6m modulates the host immune response by inhibiting dendritic cell activation and NO production by activated J774 macrophages. Finally, we observed that the amastigote forms from PPS6m and SSF isolates present low enzymatic activity that does not interfere with NO production and parasite survival in macrophages. CONCLUSIONS/SIGNIFICANCE: Our data suggest that ecto-nucleotidases present on the promastigote forms of the parasite may interfere with the establishment of the immune response with consequent impaired ability to control parasite dissemination and this may be an important factor in determining the clinical outcome of leishmaniasis.