PubMed · 1645219
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R J Shephard. 1991. Fuel for exercise.. https://pubmed.ncbi.nlm.nih.gov/1645219/
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Oxidative metabolism is the dominant source of energy for skeletal muscle. Near-infrared spectroscopy allows the non-invasive measurement of local oxygenation, blood flow and oxygen consumption. Although several muscle studies have been made using various near-infrared optical techniques, it is still difficult to interpret the local muscle metabolism properly. The main findings of near-infrared spectroscopy muscle studies in human physiology and clinical medicine are summarized. The advantages and problems of near-infrared spectroscopy measurements, in resting and exercising skeletal muscles studies, are discussed through some representative examples.
A simple model predicts the energy cost of bipedal locomotion for given speed, stride length, duty factor and shape factor. (The duty factor is the fraction of stride duration, for which a foot is on the ground, and the shape factor describes the pattern of force exerted on the ground). The parameters are varied to find the gait that minimizes metabolic energy cost, for each speed. A previous model by Alexander calculated the work that muscles have to do, but the metabolic cost (calculated in this paper) is more likely to be the principal criterion for gait selection. This model gives good predictions of human stride lengths, and of the speed at which we break into a run. It predicts lower duty factors and higher shape factors than are normally used, but the relationships between these gait parameters and speed parallel the empirical relationships.
Genetically engineered organisms overexpressing phosphofructokinase (PFK), a supposed 'regulatory' step of glycolysis, often show little or no measurable change in glycolytic or respiratory flux, although the concentrations of glycolytic intermediates may change. We have used the finite change theory of Metabolic Control Analysis (MCA) to analyse the concentrations of glycolytic metabolites in aged disks of tuber tissue from four lines of transgenic potatoes expressing different amounts of PFK that, under aerobic conditions, showed statistically indistinguishable rates of respiration. The constancy of the metabolites' concentration deviation indices for different increases in PFK expression indicated that the metabolite changes from a graded series, excluding the possibility of anomalous behaviour that might be observed in a single transgenic line. Consequently we were able to use the finite change method to validate the results of an MCA model of tuber glycolysis [Thomas, Mooney, Burrell and Fell (1997) Biochem. J. 322, 119-127]. Furthermore the metabolite changes with PFK activity are evidence that near-equilibrium steps do not transmit increased substrate concentrations down the pathway without attenuation. Our results support the view that flux increase by activation of a single enzyme early in the pathway will, contrary to expectations, be of limited effectiveness in achieving flux increases.