This study compared the effects of concentric and eccentric training on neuromuscular adaptations in young subjects. Twenty-two men and women were assigned to one of two groups: concentric (CON, n = 11) and eccentric (ECC, n = 11) training. Training consisted of 6 weeks of isokinetic exercise, performed twice weekly, starting with two sets of eight repetitions, and progressing to five sets of 10 repetitions. Subjects were tested in strength variables [concentric, eccentric, and isometric peak torque (PT), and rate of force development (RFD)], muscle conduction velocity (CV), neuromuscular activity, vastus lateralis (VL) muscle thickness, and echo intensity as determined by ultrasonography. There were similar increases in the concentric and eccentric PTs in both the CON and ECC groups (P < 0.01), but only the ECC group showed an increase in isometric PT (P < 0.001). Similarly, both groups exhibited increased VL muscle thickness, CV, and RFD, and reduced VL echo intensity (P < 0.05). Significant correlations were observed among the relative changes in the neuromuscular outcomes and training variables (e.g., total work, average PT) (r = 0.68-0.75, P < 0.05). The results showed that both training types similarly improved dynamic PT, CV, RFD, and muscle thickness and quality during the early weeks of training.

The compound muscle action potential (M wave) has been commonly used to assess the peripheral properties of the neuromuscular system. More specifically, changes in the M-wave features are used to examine alterations in neuromuscular propagation that can occur during fatiguing contractions. The utility of the M wave is based on the assumption that impaired neuromuscular propagation results in a decrease in M-wave size. However, there remains controversy on whether the size of the M wave is increased or decreased during and/or after high-intensity exercise. The controversy partly arises from the fact that previous authors have considered the M wave as a whole, i.e., without analyzing separately its first and second phases. However, in a series of studies we have demonstrated that the first and second phases of the M wave behave in a different manner during and after fatiguing contractions. The present review is aimed at five main objectives: (1) to describe the mechanistic factors that determine the M-wave shape; (2) to analyze the various factors influencing M-wave properties; (3) to emphasize the need to analyze separately the first and second M-wave phases to adequately identify and interpret changes in muscle fiber membrane properties; (4) to advance the hypothesis that it is an increase (and not a decrease) of the M-wave first phase which reflects impaired sarcolemmal membrane excitability; and (5) to revisit the involvement of impaired sarcolemmal membrane excitability in the reduction of the force generating capacity.

The single-fiber action potential (SFAP) can be modeled as a convolution of a biolectrical source (the excitation) and a transfer function, representing the electrical volume conduction. In the Dimitrov-Dimitrova (D-D) convolutional model, the first temporal derivative of the intracellular action potential (IAP) is used as the source. In this model, the ratio between the amplitudes of the second and first phases of the SFAP (which we call the PPR, after peak-to-peak ratio) increases invariably with radial distance. This is not the case of real recorded fibrillation potentials (FPs). Moreover, FPs show a wider PPR range than that which the D-D model can provide. These discrepancies suggest that the D-D model should be revised. Since the volume conduction parameters seem to have no apparent effects on the PPR, we assume that the origin of this difference lies in the excitation source. This paper presents a new analytical description of the IAP based on that expressed in the D-D model. The new approximation is shown to model FPs with a range of PPRs comparable to that observed in a set of real FPs which we used as our test signals.

Computational Intelligence in Electromyography Analysis-A Perspective on Current Applications and Future Challenges 4 potential, providing insight into the relationships between the anatomical and/or physiological properties of the fibre and the shape of the potential. 2. Modeling electrical conduction in skeletal muscle Striated muscle is composed of a large number of striated muscle cells, also called muscle fibers. These elongated, cylindrical cells are arranged parallel to one another, and each one is surrounded by a plasma membrane called the sarcolemma. Muscle contraction is created via the repeated activation of several groups of muscle fibers, each of which is governed by a single motorneuron through its axon (Lieber, 2010). Figure 1(a) shows a portion of a muscle fiber that is attached, at the neuromuscular junction, to the terminal branch of its axon.