Low-frequency fatigue at maximal and submaximal muscle contractions

Skeletal muscle force production following repetitive contractions is preferentially reduced when muscle is evaluated with low-frequency stimulation. This selective impairment in force generation is called low-frequency fatigue (LFF) and could be dependent on the contraction type. The purpose of this study was to compare LFF after concentric and eccentric maximal and submaximal contractions of knee extensor muscles. Ten healthy male subjects (age: 23.6 ± 4.2 years; weight: 73.8 ± 7.7 kg; height: 1.79 ± 0.05 m) executed maximal voluntary contractions that were measured before a fatigue test (pre-exercise), immediately after (after-exercise) and after 1 h of recovery (after-recovery). The fatigue test consisted of 60 maximal (100%) or submaximal (40%) dynamic concentric or eccentric knee extensions at an angular velocity of 60°/s. The isometric torque produced by low- (20 Hz) and high- (100 Hz) frequency stimulation was also measured at these times and the 20:100 Hz ratio was calculated to assess LFF. One-way ANOVA for repeated measures followed by the Newman-Keuls post hoc test was used to determine significant (P < 0.05) differences. LFF was evident after-recovery in all trials except following submaximal eccentric contractions. LFF was not evident after-exercise, regardless of exercise intensity or contraction type. Our results suggest that low-frequency fatigue was evident after submaximal concentric but not submaximal eccentric contractions and was more pronounced after 1-h of recovery.

Effect of praziquantel administration on hepatic stereology of mice infected with Schistosoma mansoni and fed a low-protein diet

A study was undertaken to investigate the effect of administering praziquantel (PZQ), focusing on the liver stereological findings of malnourished mice infected with Schistosoma mansoni. Thirty female Swiss Webster mice (age: 21 days; weight: 8-14 g) were fed either a low-protein diet (8%) or standard chow (22% protein) for 15 days. Five mice in each group were infected with 50 cercariae each of the BH strain (Brazil). PZQ therapy (80 mg/kg body weight, per day) was started on the 50th day of infection and consisted of daily administration for 5 days. Volume density (hepatocytes, sinusoids and hepatic fibrosis) was determined by stereology using a light microscope. Body weight gain and total serum albumin levels were always lower in undernourished mice. Our stereological study demonstrated that treatment increased both volume density of hepatocytes in mice fed standard chow (47.56%, treated group and 12.06%, control) and low-protein chow (30.98%, treated group and 21.44%, control), and hepatic sinusoids [standard chow (12.52%, treated group and 9.06%, control), low-protein chow (14.42%, treated group and 8.46%, control)], while hepatic fibrosis was reduced [standard chow (39.92%, treated group and 78.88%, control) and low-protein chow (54.60%, treated group and 70.10%, control)]. On the other hand, mice fed low-protein chow decreased density volume of hepatocytes and hepatic fibrosis. In conclusion, our findings indicate that treatment with PZQ ameliorates hepatic schistosomiasis pathology even in mice fed a low-protein diet.