Master of Science (MSc)
Faculty of Science
Fatigue is defined as any exercise induced reduction in strength or power, and can be attributed to central and peripheral components. Many central and peripheral mechanisms have been extensively studied, but few studies have looked at the changes in the intrinsic properties of motor neurons and their contribution to fatigue. Persistent inward current (PIC) is an important intrinsic property of motor neurons responsible for setting a large increase in the gain of motor output and may contribute to fatigue. Inhibitory inputs such as reciprocal inhibition (RI) have been shown to turn off PICs and reducing the gain of output. PIC measurements are typically done in animals but have recently been estimated in humans using the paired motor unit technique. Estimates of PIC were taken from paired motor unit recordings in the soleus. Estimates of PIC are calculated by using the difference (∆F) between the instantaneous firing frequency of a control unit at the recruitment and derecruitment of a test unit during an isometric triangular ramp contraction. Inhibitory input via electrical stimulation of the common peroneal nerve was used to reduce PIC in the soleus. These isometric triangular ramp contractions used to calculated ∆F were performed with and without electrical stimulation after sets of 20 fatiguing contractions in order to assess ∆F estimates of PIC before and after fatigue. Maximum voluntary contractions (MVC) were performed after each set of fatiguing contractions to quantify the amount of fatigue. The experiment was terminated after a 30% reduction in MVC. It was hypothesized that there would be a decline in ∆F estimates of PIC during a fatiguing protocol and no change in PIC during a control day in ramps without electrical stimulation. In ramps with inhibitory input via electrical stimulation (RI), ∆F estimates of PIC would not decline as significantly as ramps without electrical stimulation over the course of a fatiguing protocol. On a control day, the ramps with electrical stimulation would have a lower ∆F than ramps without electrical stimulation, and also would not change over time. On the fatigue day, MVC dropped from 347.18N ± 96.54N to 220.57N ± 65.53N, t(9) = 4.23 (p
Mendes, Kirby, "Estimates of Persistent Inward Current Decline in Human Soleus Motor Units during Fatigue" (2016). Theses and Dissertations (Comprehensive). 1794.