Sex- and age-related blood pressure response to dynamic work with small muscle masses.

Four groups of subjects of different ages and sex (group I: 20-29 years, women; group II: 20-29 years, men; group III: 30-39 years, women; group IV: 30-39 years, men) undertook dynamic one-hand work (load range 40%-80% of maximum voluntary contraction, at 60 working cycles/min) to allow a study of cardiovascular responses as shown by the resultant changes in blood pressure and heart rate. During fatiguing dynamic one-hand work, there was a large increase in systolic and diastolic blood pressures in both sexes after a few minutes. For all load levels, the systolic blood pressure was found to be higher by about 4 kPa in men (groups II and IV) than in women (groups I and III). Other age-related differences became evident in the diastolic blood pressure changes. The values obtained for the older groups were higher than those in the two younger groups. These differences in blood pressure response are possibly due to sex-related differences in the release of catecholamines, or to age-related organic changes in the vessels.

Sex- and age-related behaviour of the integrated EMG during one-arm cranking.

There are load-dependent increases in the bioelectrical activity (iEMG) of muscles of the shoulder and the right upper extremity and selected parameters of the cardiopulmonary system. At comparable loads the amplitudes of the EMG were higher in the group of men than in the group of women. The iEMG values were found to be higher in the younger group of women than in the older one. The higher values of iEMG of the younger women corresponded to a higher oxygen uptake and higher heart rate as well as to a lower physical endurance. The physical endurance limit (derived from behaviour of the EMG) was estimated at 5 watts (women) and 10 watts (men).

Contractile properties of isolated frog skeletal muscles under the influence of Na-octanoate.

Na-octanoate (2-10 mM) altered the characteristics of the isometric twitch of isolated frog skeletal muscles. The peak tension, the maximum rate of tension rose, the time to peak tension, and the half relaxation time decreased. The tetanus tension was reduced by the same amount in percent as a single isometric twitch so that no changes occurred in the twitch/tetanus relationship. The fusion frequency of tetanic contractions increased. The isotonic contractions had a reduced shortening period. The shortening velocity was not affected. The K+ induced contractures were diminished. The S-shaped curve which relates peak tension to potassium concentration was shifted to more positive potentials. The maximum contractile strength was not attained even by complete depolarization. 1-2 mM caffeine removed the octanoate effects described above. The contracture induced by 7.5 mM caffeine produced the same maximum tension as that obtained in Ringer's solution, but the contracture began later and the rise of tension was retarded. The tension development of glycerol-extracted muscles was not affected by octanoate. The results are consistent with the hypothesis that the octanoate-induced changes of muscle contraction are due to a reduced Ca++ release from cellular stores.