ASTRAND, I., P.-0. ASTRAND, E. H. CHRISTENSEN and R. HEDMAK. Intermittent muscular work. Acta physiol. scand. 1960. 48. 448-453. -The physiological effect of rest pauses on a non-steady state work (2,160 kpm/min) was studied. A physically well trained subject performed in one hour a total amount of 64,800 kpm on a bicycle ergometer by intermittent work with 0.5, 1, 2 or 3 min periods of work and rest. Total 0, intake, total pulmonary ventilation, total number of heart beats and blood lactic acid concentration during the work hour and during recovery were determined. I t was found that the heavy work when split into short periods of work and rest (of 0.5 or 1 min duration) was transformed to a submaximal load on circulation and respiration and was well tolerated during one hour. With longer periods (of 2 or
ASTRAND, I., P.-0. ASTRAND, E. H. CHRISTENSEN and R. HEDMAN.Myohemoglobin as an oxygen-store in man. Acta physiol. scand. 1960. 48. 454-460. -The aim of the present research was to investigate further the possible r81e of myohemoglobin as an oxygen-store during the initial stage of muscular work. One subject worked intermittently with a work load of 2,520 kpm/min with varied duration of work and rest pauses on a bicycle ergometer. A highly significant difference in the blood lactic acid concentration during the experimental time of 30 min was found, at work with short work periods (10 sec, lactic acid concentration about 10-20 mg per 100 ml) compared with relative long ones (60 sec, lactic acid concentration 1 10-140 mg per 100 ml). The conclusion was drawn that the first type of work is performed aerobically. The calculated oxygen demand, during the work period of 10 sec, however, does not correspond to the measured oxygen intake. A deficit of about 0.43 1 0, for each period of work will occur. It was suggested that this amount of 0.43 1 0 , is supplied to the working muscle mainlyfrom oxymyohemoglobin. This store function of myohemoglobin is discussed in relation to the present findings and to the results mentioned in the literature.
Intermittent running on a tread mill at a speed of 20 km/h (12.4 miles/h) is analysed and a comparison between this work and continuous running at the same speed has been done. The present results are in agreement with the assumption that stored oxygen plays an important role for the oxygen supply during short spells of heavy work. When running intermittent 6.67 km in 30 min (effective work 20 min and rest 10 min), a trained subject attained a total O2 uptake of 150 1. With an O2 uptake of 0.4 1/min at rest standing at the tread mill, or 4 1 per 10 min of rest, 146 1 O2 are due to the 20 min of work. The actual uptake at work was only 101 1 and if normal values are assumed during rest pauses, a deficit in oxygen transport of 45 1 arises during the 20 min of actual work. This quantity will be taken up during the 120 rest pauses of 5 sec each. Two thirds of the oxygen demand during the 120 work periods of 10 sec each will accordingly be supplied by oxygen transported with the blood during work, and one third will be covered by a reduction in the available oxygen stores in the muscles, which in turn will be reloaded during the subsequent 5 sec rest periods. Respiratory and circulatory functions at intermittent and continuous running with special reference to maximal values are discussed. Research on intermittent work may open up a new field in work physiology.
Blood was drawn from cross-country skiers at 1–3 min after the finish in competitions on distances from 10 to 85 km and the blood lactate determined. Despite a maximal effort of the skiers, accentuated at the end of the race, there was a successive decrease in the blood lactate concentration with work time. After a 10-km race, work time 35–36 min, the average was 139 mg/100 ml of blood (12.5 mEq/liter); after a 30-km race, with a time of 1 hr 50 min-1 hr 56 min, the mean value was 68 mg/100 ml (6.1 mEq/liter); and after a 50-km race, work time 3 hr 6 min-3 hr 18 min, 39 mg/100 ml (3.5 mEq/liter). A lactate concentration exceeding 100 mg/100 ml is a common finding after maximal muscular exercise involving large muscles. The explanation for the low values after prolonged maximal work, indicating a different kind of fatigue, is presently obscure. Data are presented on the oxygen uptake attained during skiing at actual racing speed (average Vo2 = 4.45 liters/min). Submitted on July 16, 1962
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