Observations on the course of the metabolic events accompanying mild exercise

Blood lactate accumulation in intermittent supramaximal exercise

Blood lactate accumulation rate and oxygen consumption have been studied in six trained male runners, aged 20 to 30 years. Subjects ran on a treadmill at a rate representing 172 +/- 5% VO2max for four 45 s sessions, separated by 9 min rest periods. Oxygen consumption was measured throughout. Blood lactate was determined in samples taken from the ear and VO2 was measured at the end of each exercise session, and two, five and nine minutes later. After the fourth exercise session, the same measurements were made every five min for 30 min. 4 subjects repeated a single exercise of the same type, duration and intensity and the same measurements were taken. With repetitive intermittent exercise, gradual increases in blood lactate concentration [( LA]b) occurred, whereas its rate of accumulation (delta[LA]b) decreased. The amount of oxygen consumed during each 45 s exercise session remained unchanged for a given subject. After cessation of intermittent exercise, the half-time of blood lactate was 26 min, whereas it was only 15 min after a single exercise session. VO2 values, on the other hand, returned to normal after 15 to 20 min. All other conditions being equal, the gradual decrease in delta[LA]b during intermittent exercise could be explained if the lactate produced during the first exercise session is used during the second period, and/or if the diffusion space of lactate increases. The diffusion space seems to be multi-compartmental on the basis of half-time values noted for [LA]b after intermittent exercise, compared with those noted after a single exercise session.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for phosphate as a mediator of functional hyperaemia in skeletal muscles

Maximal twitch contractions of fast muscles of the cat caused an increase in phosphate concentration in the venous plasma from them: this efflux was greater as the contraction frequency was increased. At any given frequency of contraction, the phosphate efflux from contracting gastrocnemius was less than that from tibialis anterior and extersor digitorum longus, which have a higher proportion of fast fibres and exhibit greater functional hyperaemia. Soleus muscles, when contracting, released hardly any additional phosphate, except in the one experiment in which the muscle exhibited a functional hyperaemia. There was thus a consistent relationship between the extent of functional hyperaemia and phosphate efflux in different muscles and within any one group of muscles. Inorganic phosphate, given close arterially as NaH2PO4, was shown to be vasodilator.NaH2PO4 was much more potent than Na2HPO4, though this did not seem due simply to the associated change of pH. The functional hyperaemia of fast muscles could be matched, qualitatively and quantitatively, by injections or infusions of NaH2PO4. The possibility is discussed that the contraction hyperaemia of fast muscles is functionally related to phosphate release into the interstitial fluid during contractions.

Cardiovascular response to exercise under increasing doses of chlorthalidone

Five male subjects with essential hypertension received chlorthalidone at each of four dose levels (25, 50, 100, and 200 mg/day) for eight week periods each preceded by an eight week placebo period. Dosage order was randomized and double-blind. During the last week of each active and placebo period an upright bicycle exercise study was carried out at three loads (100, 200, 300 kpm/min) for 6 min each. Oxygen consumption at the maximal workload was 42% of predicted at a heart rate of 170. During placebo therapy, increasing workloads were associated with a progressive increase in blood pressure, heart rate, and pressure-rate index (systolic pressure times heart rate). With increasing doses of chlorthalidone up to 100 mg/day, there was a progressive reduction in blood pressure and pressure-rate index. At 200 mg/day there were paradoxical increases in diastolic pressures, heart rates and pressure-rate indices above values observed at 100 mg/day. With increasing doses of chlorthalidone, there was a progressive increase in arterial blood CO2 content and pH. Increasing workloads were associated with increased arterial blood lactate and decreased arterial blood lactate and decreased arterial blood pH. The changes in lactate and pH were not different at the different dose levels. The best antihypertensive effect in these exercising subjects was observed at a daily dose of 100 mg of chlorthalidone. The exercise response was useful in the determination of potentially adverse hemodynamic consequences of the larger dose of chlorthalidone.