Human locomotory performance is dependent upon the ability of skeletal muscle to generate mechanical power, and sustain that power -that is, resist fatigue. Not surprisingly the factors influencing this capability have attracted the attention of many investigators dating back to and beyond the beginning of this century (see e.g. Benedict & Cathcart, 1913;Krogh & Lindhard, 1920;Hill, 1922;Lupton, 1923;Dickenson, 1928;Wilkie, 1960Wilkie, , 1981Carnevale & Gaesser, 1991;McNaughton & Thomas, 1996). However, although there are a number of studies which have examined the maximum power of human locomotory muscles, and many more which have examined the constraints and limitations to sustained exercise -especially with respect to aerobic and anaerobic energy supply -rather few data are available from studies which have examined, in the same subjects, the relationship between maximum power and the power delivered in sustained exercise, and there are almost no data on the effect that movement frequency has on that relationship. In part, this paucity of data is due to the technical difficulty of measuring maximal power output at a constant known movement frequency in human locomotion. In seeking to address this difficulty, one of us developed an isokinetic cycle ergometer which enabled the maximum power generated by the main locomotory muscles to be measured over a range of movement frequencies (Sargeant et al. 1981). Subsequently, the ergometer system was modified so that the power could be measured continuously at the foot-pedal interface either during submaximal exercise, or during a maximum effort with the system switched to its isokinetic The effect of different pedalling rates (40, 60, 80, 100 and 120 rev min¢) on power generating capability, oxygen uptake (ýOµ) and blood lactate concentration [La]b during incremental tests was studied in seven subjects. No significant differences in ýOµ,max were found (mean ± s.d., 5.31 ± 0.13 l min¢). The final external power output delivered to the ergometer during incremental tests (PI,max) was not significantly different when cycling at 60, 80 or 100 rev min¢ (366 ± 5 W). A significant decrease in PI,max of •60 W was observed at 40 and 120 rev min¢ compared with 60 and 100 rev min¢, respectively (P < 0.01). At 120 rev min¢ there was also a pronounced upward shift of the ýOµ-power output (ýOµ-P) relationship. At 50 W ÄýOµ between 80 and 100 rev min¢ amounted to +0.43 l min¢ but to +0.87 l min¢ between 100 and 120 rev min¢. The power output corresponding to 2 and 4 mmol l¢ blood lactate concentration (P[La]2 and P[La]4 ) was also significantly lower (> 50 W) at 120 rev min¢ (P < 0.01) while pedalling at 40, 60, 80 and 100 rev min¢ showed no significant difference. The maximal peak power output (PM,max) during 10 s sprints increased with pedalling rate up to 100 rev min¢. Our study indicates that with increasing pedalling rate the reserves in power generating capability increase, as illustrated by the PI,maxÏPM,max ratio (54.8, 44.8, 38.1, 34.6, 29.2%), the P[La]4ÏPM,max ratio (50.4...
The negative relationship between testosterone and inflammatory cytokines has been reported for decades, although the exact mechanisms of their interactions are still not clear. At the same time, little is known about the relation between androgens and acute phase proteins. Therefore, in this investigation, we aimed to study the relationship between androgen status and inflammatory acute phase reactants in a group of men using multi-linear regression analysis. Venous blood samples were taken from 149 men ranging in age from 18 to 77 years. Gonadal androgens [testosterone (T) and free testosterone (fT)], acute phase reactants [C-reactive protein (CRP), ferritin (FER), alpha-1-acid glycoprotein (AAG), and interleukin-6 (IL-6)], cortisol (C), and lipid profile concentrations were determined. It was demonstrated that the markers of T and fT were negatively correlated with all acute phase proteins (CRP, FER, and AAG; p < 0.02) and the blood lipid profile [total cholesterol (TC), low-density lipoprotein (LDL), and triglycerides (TG); p < 0.03]. Multivariate analysis showed that T, fT, and the fT/C ratio were inversely correlated with the CRP, AAG, and FER concentrations independently of age and blood lipids. When adjustment for BMI was made, T, fT, and the fT/C ratio were negatively correlated with the AAG concentrations only. In addition, it was demonstrated that gonadal androgens were positively correlated with physical activity level (p < 0.01). We have concluded that a lowered serum T concentration may promote inflammatory processes independently of adipose tissue and age through a reduced inhibition of inflammatory cytokine synthesis, which leads to enhanced acute phase protein production. Therefore, a low serum T concentration appears to be an independent risk factor in the development of atherosclerosis and cardiovascular diseases. Moreover, the positive correlation between testosterone and physical activity level suggests that exercise training attenuates the age-related decrease in gonadal androgens and, in this way, may reduce the enhancement of systemic low-grade inflammation in aging men.
Skeletal muscles are an important reservoir of nitric oxide (NO•) stored in the form of nitrite [NO2−] and nitrate [NO3−] (NOx). Nitrite, which can be reduced to NO• under hypoxic and acidotic conditions, is considered a physiologically relevant, direct source of bioactive NO•. The aim of the present study was to determine the basal levels of NOx in striated muscles (including rat heart and locomotory muscles) with varied contents of tissue nitrite reductases, such as myoglobin and mitochondrial electron transport chain proteins (ETC-proteins). Muscle NOx was determined using a high-performance liquid chromatography-based method. Muscle proteins were evaluated using western-immunoblotting. We found that oxidative muscles with a higher content of ETC-proteins and myoglobin (such as the heart and slow-twitch locomotory muscles) have lower [NO2−] compared to fast-twitch muscles with a lower content of those proteins. The muscle type had no observed effect on the [NO3−]. Our results demonstrated that fast-twitch muscles possess greater potential to generate NO• via nitrite reduction than slow-twitch muscles and the heart. This property might be of special importance for fast skeletal muscles during strenuous exercise and/or hypoxia since it might support muscle blood flow via additional NO• provision (acidic/hypoxic vasodilation) and delay muscle fatigue.
We demonstrated for the first time that NNMT - MNA pathway is activated by a single bout of endurance exercise. Interestingly, exercise-induced activation of NNMT in the liver involves IL-6, while the rise in MNA concentration in plasma was partially IL-6-independent. Taking into the consideration the pharmacological activity of MNA, IL-6-dependent and IL-6-independent activation of NNMT, may contribute to the exercise capacity. The physiological role of NNMT in the exercise warrant further studies.
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