a1_The effect of different muscle shortening velocity was studied during cycling at a pedalling rate of 60 and 120 rev.min-1 on the [K+]v in 21 healthy young men (aged 22.5±2.2 years, body mass 72.7±6.4 kg, VO2max 3.720±0.426 l . min-1) performing an incremental exercise test until exhaustion. The power output increased by 30 W every 3 min, using an electrically controlled ergometer Ergoline 800S (see Zoladz et al. J. Physiol. 488: 211-217, 1995). The test was performed twice: once at a cycling frequency of 60 rev.min-1 (test A) and a few days later at frequency of 120 rev.min-1 (test B). At rest and at the end of each step (i.e. the last 15 s) antecubital venous blood samples for [K+]v were taken. Gas exchange variables were measured continuously (breath-by-breath) using Oxycon Champion Jaeger. The pre-exercise [K+]v in both tests was not significantly different amounting to 4.24±0.36 mmol.l-1 in test A, and 4.37±0.45 mmol.l-1 in test B. However, the [K+]v during cycling at 120 rev.min-1 was significantly higher (p<0.001, ANOVA for repeated measurements) at each power output when compared to cycling at 60 rev.min-1. The maximal power output reached 293±31 W in test A which was significantly higher (p<0.001) than in test B, which amounted to 223±40 W. The VO2max values in both tests reached 3.720±0.426 l.min-1 vs 3.777±0.514 l.min-1. These values were not significantly different. When the [K+]v was measured during incremental cycling exercise, a linear increase in [K+]v was observed in both tests. However, a significant (p<0.05) upward shift in the [K+]v and a % VO2max relationship was detected during cycling at 120 rev.min-1. The [K+]v measured at the VO2max level in tests A and B amounted to 6.00±0.47 mmol.l-1 vs 6.04±0.41 mmol.l-1, respectively., a2_This difference was not significant. It can thus be concluded that a) generation of the same external mechanical power output during cycling at a pedaling rate of 120 rev.min-1 causes significantly higher [K+]v changes than when cycling at 60 rev.min-1, b) the increase of venous plasma potassium concentration during dynamic incremental exercise is linearly related to the metabolic cost of work expressed by the percentage of VO2max (increase as reported previously by Vollestad et al. J. Physiol. Lond. 475: 359-368, 1994), c) there is a tendency towards upward shift in the [K+]v and % VO2max relation during cycling at 120 rev.min-1 when compared to cycling at 60 rev.min-1., J. A. Zoladz, K. Duda, J. Majerczak, P. Thor., and Obsahuje bibliografii
The relationships between exercise and metabolites as well as between exercise and sarcoplasmic reticulum function were studied in gastrocnemius muscle of ovariectomized-trained rats. Prolonged moderate-intensity exercise, treadmill up-hill run for 90 min with a 10° incline, decreased the muscle glycogen content. Exercise until exhaustion further lowered the glycogen concentration to 13 % of the control, together with a significant decrease of ATP and glucose-6-phosphate concentrations. Also, Ag+-induced Ca2+release, measured in whole muscle homogenate, showed a 30 % reduction on exhaustion, while Ca2+ uptake was unaffected by this exercise. ATPase activities, of both homogenate and SR vesicles, and Ca2+ transport in the latter preparation were not altered on exhaustion. It could be concluded from these results that muscular fatigue in ovariectomized rats after aerobic exercise is caused by the change in energy supply and Ca2+ release from the SR, this latter possibly due to metabolites generated by the exercise., I. Gigli, L. E. Bussmann., and Obsahuje bibliografii