Muscle Fiber Diameter and Density Alterations after Stroke Examined by Single-Fiber EMG

This study presents single-fiber electromyography (EMG) analysis for assessment of paretic muscle changes after stroke. Single-fiber action potentials (SFAPs) were recorded from the first dorsal interosseous (FDI) muscle bilaterally in 12 individuals with hemiparetic stroke. The SFAP parameters, including the negative peak duration and the peak-peak amplitude, were measured and further used to estimate muscle fiber diameter through a model based on the quadratic function. The SFAP parameters, fiber density, and muscle fiber diameter derived from the model were compared between the paretic and contralateral muscles. The results show that SFAPs recorded from the paretic muscle had significantly smaller negative peak duration than that from the contralateral muscle. As a result, the derived muscle fiber diameter of the paretic muscle was significantly smaller than that of the contralateral muscle. The fiber density of the paretic muscle was significantly higher than that of the contralateral muscle. These results provide further evidence of remodeled motor units after stroke and suggest that paretic muscle weakness can be due to both complex central and peripheral neuromuscular alterations.

Use of Immunofluorescence Technique to Perform a Quantitative Analysis of Masseter Muscle Fibers in Unilateral Posterior Crossbite: A Pilot Study

Unilateral posterior crossbite is a type of malocclusion that involves morpho-functional characteristics of masticatory muscle, such as the masseter: electrophysiological data have shown that the affected side works less than the contralateral muscle, which shows a normal or increased activity, probably in order to compensate for the affected side. The aim of present work was to measure the diameter and the cross-sectional area of ipsilateral and contralateral muscle fibers to verify if hypertrophy and/or hypotrophy take place in this malocclusion. We used immunofluorescence pictures to measure, using ImageJ software, the diameter and the cross-sectional area of fibers from control and crossbite groups; after that, the data were processed to perform statistical analyses. Results show that the fiber diameters of contralateral muscle are larger than the diameters of ipsilateral and control fibers, and that this difference is statistically significant. No statistically significant difference was found between the fiber diameters of the ipsilateral and control muscles. All these data suggest that, during unilateral posterior crossbite, morphological changes take place in the contralateral masseter muscle, which undergoes hypertrophy, probably to compensate for the low activity of the affected muscle.

Extracellular Matrix Behaviour in Masseter Muscle of Patients Affected by Unilateral Posterior Crossbite: An Immunofluorescence Study

Unilateral posterior crossbite is a malocclusion disease that involves morpho-functional characteristics of masseter muscle; a normal or increased activity of contralateral muscle and a reduced activity of the ipsilateral muscle during unilateral crossbite have been shown. Since the extracellular matrix plays a key role in in mechano-transduction of transmitting forces during muscle contraction, the aim of the present study was to analyse the behaviour of extracellular matrix in this type of malocclusion through immunofluorescence reactions against laminin, collagen IV, MMP-2 and MMP-9. Our results show an increased expression of Laminin, Collagen IV, and MMP-9 in the contralateral side if compared to the ipsilateral side. No differences have been found in MMP-2 expression between contralateral and ipsilateral muscles. Since the increased expression of Laminin, Collagen IV and MMP-9 is associated with muscle hypertrophy and MMP-2 is associated with muscle atrophy, our results support the existence of a hypertrophic response of contralateral muscle during unilateral posterior crossbite that probably aims to compensate the altered function of the ipsilateral one.

Immunofluorescence Evaluation of Myf5 and MyoD in Masseter Muscle of Unilateral Posterior Crossbite Patients

A unilateral posterior crossbite is a malocclusion where the low activity of the affected masseter muscle is compensated by the contralateral muscle hypertrophy. It is still unknown if, in the same condition, myogenesis with new fibre formation takes place. Aim: the aim of the present study was to evaluate the expression of myogenesis markers, such as Myf5 and MyoD, in masseter muscles of unilateral posterior crossbite patients. Materials and methods: biopsies from fifteen surgical patients with unilateral posterior crossbites have been analysed by immunofluorescence reactions. The results show the expression of Myf5 and MyoD in the contralateral muscle but not in the ipsilateral one. Moreover, statistical analysis shows the higher number of satellite cells in the contralateral side if compared to the ipsilateral one. Conclusions: these results suggest that in contralateral muscle, hyperplastic events take place, as well as hypertrophy.

Contralateral Muscle Imbalances and Physiological Profile of Recreational Aerial Athletes

Background: Aerial fitness is quickly gaining popularity; however, little is known regarding the physiological demands of aerial athletes. The purpose of the study was to examine contralateral muscle imbalances, compare dominant versus non-dominant hamstrings-to-quadriceps (H:Q) ratios, and to establish a physiological profile of recreational aerial athletes. Methods: Thirteen aerialist women visited a local aerial studio to participate in a data collection session to examine isometric levels of upper and lower body strength, muscle endurance, flexibility, balance, and cardiovascular fitness. Results: No significant differences were found between dominant and non-dominant hand grip strength (p = 0.077), dominant and non-dominant isometric knee flexion (p = 0.483), dominant and non-dominant isometric knee extension (p = 0.152), or dominant and non-dominant isometric H:Q ratios (p = 0.102). In addition, no significant difference was found between isometric dominant H:Q ratio and the widely-used value of 0.60 (p = 0.139). However, isometric non-dominant H:Q ratio was significantly lower than the 0.60 criterion (p = 0.004). Aerial athletes demonstrated to have excellent flexibility, balance, cardiorespiratory fitness, and average strength. Conclusions: Aerial fitness may be another recreational activity that could be used to maintain higher levels of flexibility, balance, cardiorespiratory fitness, and strength. Aerialists may want to consider focusing on strengthening the lower body and balancing the hamstrings and quadriceps muscle strength.