Classical references

Hohwü Christensen E, Hedman R, Holmdahl I. The influence of rest pauses on mechanical efficiency. Ästrand I, Ästrand P-O, Hohwü Christensen E,

Hedman R. Intermittent muscular work. Astrand I, Astrand P-O, Hohwü Christensen E, Hedman R. Myohemoglobin as an oxygen-store in man. Acta PhysiolScand i960; 48: 443-460. In this series of three papers, the authors describe the energy expenditure and metabolism resulting from different application of work and rest periods while working on light and heavy workloads. The papers have had a large impact because they were the first, following the initial observations of Karrasch and Müller (Arbeitsphysiologie 1951; 14: 369-382), to attract interest to the physiology and metabolism of intermittent work.

In the first paper, data are given to support the fact that the energy cost per kJ of work is the same or practically the same whether the work is performed continuously for i h with an easy load or discontinuously with heavier loads. The results disputed the hypothesis of Müller and coworkers that pauses would significantly increase the oxygen demand for a subsequent work period. In the second paper, the authors showed that an extremely heavy workload, when split into short periods of work and rest, was transformed to a submaximal load on circulation and respiration. To explain the low lactate concentrations after intermittent work (work periods of 10-15 s), the authors proposed two alternative hypotheses: (i) that the rate of formation of lactic acid during a heavy workload is the same, independent of the length of the work period, but that lactic acid during the short periods of rest is eliminated almost at the same rate; and (ii) that the formation of lactic acid during the short work periods is reduced to a minimum because it can take place almost aerobically. From the results in the third paper, the authors dismiss the first hypothesis and conclude that approximately 0.43 L O2 must have been available in the working muscles at the beginning of each new work period. It is proposed that this amount of oxygen is bound to myohemoglobin (myoglobin) in the muscles and is being 'reloaded' during the pauses to constitute approximately half of the amount of oxygen used during a 10-s work period.

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