Medicine Amp Science in Sports Amp Exercise, Jun 1, 2005
The aim of this study was investigate ATP economy of force maintenance in the human tibialis ante... more The aim of this study was investigate ATP economy of force maintenance in the human tibialis anterior muscle during 60 s of anaerobic voluntary contraction at 50% of maximum voluntary contraction (MVC). ATP turnover rate was evaluated using P magnetic resonance spectroscopy (P-MRS). The total volume of ankle dorsiflexor muscles was assessed by H magnetic resonance imaging (MRI) (H-MRI), and the fiber type composition of the tibialis anterior muscle was evaluated using histochemical analysis of muscle biopsies. The tibialis anterior muscle occupied 59.7 +/- 0.6% (mean +/- SEM) of the total ankle dorsiflexor muscle volume, which was 267 +/- 10 cm. Relative cross-sectional areas occupied by Type I, IIA, and IIB fibers in the tibialis anterior were 69.3 +/- 2.2, 27.4 +/- 2.76, and 3.2 +/- 1.0%, respectively. ATP economy of force maintenance did not change significantly during the 60-s contraction. It averaged at 4.81 +/- 0.42 N.s.micromol-1, and correlated with the relative cross-sectional area of the muscle occupied by Type I fiber (r = 0.73, P < 0.01). For the second half of the contraction, subjects dropping in force showed lower ATP economy compared with those maintaining the force (3.7 +/- 0.6 vs 5.3 +/- 0.6 N.s.micromol-1; P < 0.05). It is argued that the unchanged ATP economy of force maintenance during the voluntary contraction could be due to an increase in the ATP economy of contracting muscle fibers offsetting the effects of increased temperature and low ATP economy of Type II fibers. Mechanical interaction between motor units could also act to improve ATP economy of force maintenance.
Biochemical and Biophysical Research Communications, Sep 30, 1986
Periportal and perivenous hepatocytes from rat liver were isolated by combined digitonin-collagen... more Periportal and perivenous hepatocytes from rat liver were isolated by combined digitonin-collagenase perfusion, and gluconeogenesis, urea synthesis and fatty acid synthesis was measured both in freshly isolated cells and in primary culture. A periportal zonation of gluconeogenesis and urea synthesis of about 3 and 1.5 fold, respectively, was observed. This zonation persisted unchanged for 23 hours in culture under identical conditions of incubation for periportal and perivenous cells. Fatty acid synthesis was not zonated.
A double-blind placebo-controlled cross-over trial was undertaken to evaluate the effect of antio... more A double-blind placebo-controlled cross-over trial was undertaken to evaluate the effect of antioxidant supplementation on maximal oxygen uptake during bicycling, 31-phosphorus nuclear magnetic response spectroscopy (31P-NMRS) detected muscle energy metabolism during plantar flexion and muscle fatigue evaluated by 1-s electrical stimulation at low (10 Hz) and high (50 Hz) frequency. Seven male triathletes received daily oral antioxidant supplementation in capsule form including 100 mg coenzyme Q10 (CoQ10), 600 mg ascorbic acid and 270 mg alpha-tocopherol or placebo over a 6-week interval. Serum concentration of CoQ10 was significantly higher in the antioxidant phase (1.80+/-1 microg x ml(-1), mean +/- SD) than control (0.9+/-0.21 microg ml(-1)) or placebo phase (0.9+/-0.3 microg x ml(-1)) (P<0.01). Maximal oxygen uptake was 63.8+/-3.0 ml x min(-1) x kg(-1) in the control phase, and did not change significantly in the antioxidant (67.6+/-10.8 ml x min(-1) x kg(-1)) or the placebo phase (61.9+/-4.5 ml x min(-1) x kg(-1)). The combined 31P-NMRS/low frequency fatigue test (plantar flexion of the foot) did not show differences in the gastrocnemius muscle pH (6.77+/-0.14), phosphocreatine reduction at the end of exercise (23+/-14% of rest) and half-time for recovery of phosphocreatine (33+/-12 sec) between the placebo and the antioxidant trial. No difference in muscle fatigue at 10 Hz electrical stimulation was found between the three phases. In conclusion, the results demonstrate no effect of antioxidative vitamin supplementation on maximal oxygen uptake, muscle energy metabolism or muscle fatigue in triathletes.
Muscle phosphoglycerate mutase deficiency (PGAMD) is a rare, recessively inherited metabolic myop... more Muscle phosphoglycerate mutase deficiency (PGAMD) is a rare, recessively inherited metabolic myopathy that affects one of the last steps of glycolysis. Clinically, PGAMD resembles muscle phosphorylase deficiency (McArdle disease) and phosphofructokinase deficiency (PFKD). However, it is unknown whether PGAMD is associated with a second-wind phenomenon during exercise, as in McArdle disease, and whether patients with PGAMD, like patients with PFKD and McArdle disease, benefit from supplementation with fuels that bypass the metabolic block. To investigate whether fuels that bypass the metabolic block can improve exercise capacity or whether exercise capacity improves during sustained exercise. Single-blind, placebo-controlled investigation of the effects of glucose, lactate, and intralipid on work capacity in patients with PGAMD. National University Hospital, University of Copenhagen, and Neuromuscular Center, Institute for Exercise and Environmental Medicine. Patients Two unrelated men (21 and 26 years old) with PGAMD who since their teens had experienced muscle cramps, muscle pain, and episodes of myoglobinuria provoked by brief vigorous exercise, 4 patients with McArdle disease (mean +/- SD age, 32 +/- 5 years) with 0% residual phosphorylase activity in muscle, and 6 healthy, untrained male volunteers (mean +/- SD age, 23 +/- 1 years) were studied. Using constant and variable workload protocols on a cycle ergometer, it was investigated whether a spontaneous second wind occurs during exercise in patients with PGAMD, and using a constant workload protocol followed by an incremental load to exhaustion, it was tested whether infusion of lactate, glucose, or intralipid alters the exercise tolerance in PGAMD. Whether a second wind occurs during exercise and whether fuels that bypass the metabolic block can improve exercise and oxidative capacity. In contrast to patients with McArdle disease, with whom they share many clinical features, in patients with PGAMD, cycle exercise and oxidative capacity are virtually normal, a second wind does not occur, and lipid and lactate supplements do not improve exercise capacity. Although the clinical manifestations of PGAMD mimic McArdle disease with respect to the presence of exertional muscle cramps, rhabdomyolysis, and myoglobinuria, this study shows that cycle exercise responses are strikingly different.
Central fatigue is the term used to describe when muscle contractions become limited by the abili... more Central fatigue is the term used to describe when muscle contractions become limited by the ability of the central nervous system to recruit motor neurones. Central fatigue becomes manifest when the effort is intense and is associated not only with reduced strength but also with an inability to maintain the contraction. The contractions thereby resemble those developed during partial neuromuscular blockade that mainly affect slow twitch muscle fibres. We suggest that central fatigue also manifests as a reduction in the ratio between the brain's uptake of oxygen relative to that of carbohydrate from 6 to less than 3. This imbalance between oxygen and glucose plus lactate uptake remains unsolved, but glycogen and accumulation of intermediates of metabolism are likely to play a key role.
Medicine Amp Science in Sports Amp Exercise, Jun 1, 2005
The aim of this study was investigate ATP economy of force maintenance in the human tibialis ante... more The aim of this study was investigate ATP economy of force maintenance in the human tibialis anterior muscle during 60 s of anaerobic voluntary contraction at 50% of maximum voluntary contraction (MVC). ATP turnover rate was evaluated using P magnetic resonance spectroscopy (P-MRS). The total volume of ankle dorsiflexor muscles was assessed by H magnetic resonance imaging (MRI) (H-MRI), and the fiber type composition of the tibialis anterior muscle was evaluated using histochemical analysis of muscle biopsies. The tibialis anterior muscle occupied 59.7 +/- 0.6% (mean +/- SEM) of the total ankle dorsiflexor muscle volume, which was 267 +/- 10 cm. Relative cross-sectional areas occupied by Type I, IIA, and IIB fibers in the tibialis anterior were 69.3 +/- 2.2, 27.4 +/- 2.76, and 3.2 +/- 1.0%, respectively. ATP economy of force maintenance did not change significantly during the 60-s contraction. It averaged at 4.81 +/- 0.42 N.s.micromol-1, and correlated with the relative cross-sectional area of the muscle occupied by Type I fiber (r = 0.73, P < 0.01). For the second half of the contraction, subjects dropping in force showed lower ATP economy compared with those maintaining the force (3.7 +/- 0.6 vs 5.3 +/- 0.6 N.s.micromol-1; P < 0.05). It is argued that the unchanged ATP economy of force maintenance during the voluntary contraction could be due to an increase in the ATP economy of contracting muscle fibers offsetting the effects of increased temperature and low ATP economy of Type II fibers. Mechanical interaction between motor units could also act to improve ATP economy of force maintenance.
Biochemical and Biophysical Research Communications, Sep 30, 1986
Periportal and perivenous hepatocytes from rat liver were isolated by combined digitonin-collagen... more Periportal and perivenous hepatocytes from rat liver were isolated by combined digitonin-collagenase perfusion, and gluconeogenesis, urea synthesis and fatty acid synthesis was measured both in freshly isolated cells and in primary culture. A periportal zonation of gluconeogenesis and urea synthesis of about 3 and 1.5 fold, respectively, was observed. This zonation persisted unchanged for 23 hours in culture under identical conditions of incubation for periportal and perivenous cells. Fatty acid synthesis was not zonated.
A double-blind placebo-controlled cross-over trial was undertaken to evaluate the effect of antio... more A double-blind placebo-controlled cross-over trial was undertaken to evaluate the effect of antioxidant supplementation on maximal oxygen uptake during bicycling, 31-phosphorus nuclear magnetic response spectroscopy (31P-NMRS) detected muscle energy metabolism during plantar flexion and muscle fatigue evaluated by 1-s electrical stimulation at low (10 Hz) and high (50 Hz) frequency. Seven male triathletes received daily oral antioxidant supplementation in capsule form including 100 mg coenzyme Q10 (CoQ10), 600 mg ascorbic acid and 270 mg alpha-tocopherol or placebo over a 6-week interval. Serum concentration of CoQ10 was significantly higher in the antioxidant phase (1.80+/-1 microg x ml(-1), mean +/- SD) than control (0.9+/-0.21 microg ml(-1)) or placebo phase (0.9+/-0.3 microg x ml(-1)) (P<0.01). Maximal oxygen uptake was 63.8+/-3.0 ml x min(-1) x kg(-1) in the control phase, and did not change significantly in the antioxidant (67.6+/-10.8 ml x min(-1) x kg(-1)) or the placebo phase (61.9+/-4.5 ml x min(-1) x kg(-1)). The combined 31P-NMRS/low frequency fatigue test (plantar flexion of the foot) did not show differences in the gastrocnemius muscle pH (6.77+/-0.14), phosphocreatine reduction at the end of exercise (23+/-14% of rest) and half-time for recovery of phosphocreatine (33+/-12 sec) between the placebo and the antioxidant trial. No difference in muscle fatigue at 10 Hz electrical stimulation was found between the three phases. In conclusion, the results demonstrate no effect of antioxidative vitamin supplementation on maximal oxygen uptake, muscle energy metabolism or muscle fatigue in triathletes.
Muscle phosphoglycerate mutase deficiency (PGAMD) is a rare, recessively inherited metabolic myop... more Muscle phosphoglycerate mutase deficiency (PGAMD) is a rare, recessively inherited metabolic myopathy that affects one of the last steps of glycolysis. Clinically, PGAMD resembles muscle phosphorylase deficiency (McArdle disease) and phosphofructokinase deficiency (PFKD). However, it is unknown whether PGAMD is associated with a second-wind phenomenon during exercise, as in McArdle disease, and whether patients with PGAMD, like patients with PFKD and McArdle disease, benefit from supplementation with fuels that bypass the metabolic block. To investigate whether fuels that bypass the metabolic block can improve exercise capacity or whether exercise capacity improves during sustained exercise. Single-blind, placebo-controlled investigation of the effects of glucose, lactate, and intralipid on work capacity in patients with PGAMD. National University Hospital, University of Copenhagen, and Neuromuscular Center, Institute for Exercise and Environmental Medicine. Patients Two unrelated men (21 and 26 years old) with PGAMD who since their teens had experienced muscle cramps, muscle pain, and episodes of myoglobinuria provoked by brief vigorous exercise, 4 patients with McArdle disease (mean +/- SD age, 32 +/- 5 years) with 0% residual phosphorylase activity in muscle, and 6 healthy, untrained male volunteers (mean +/- SD age, 23 +/- 1 years) were studied. Using constant and variable workload protocols on a cycle ergometer, it was investigated whether a spontaneous second wind occurs during exercise in patients with PGAMD, and using a constant workload protocol followed by an incremental load to exhaustion, it was tested whether infusion of lactate, glucose, or intralipid alters the exercise tolerance in PGAMD. Whether a second wind occurs during exercise and whether fuels that bypass the metabolic block can improve exercise and oxidative capacity. In contrast to patients with McArdle disease, with whom they share many clinical features, in patients with PGAMD, cycle exercise and oxidative capacity are virtually normal, a second wind does not occur, and lipid and lactate supplements do not improve exercise capacity. Although the clinical manifestations of PGAMD mimic McArdle disease with respect to the presence of exertional muscle cramps, rhabdomyolysis, and myoglobinuria, this study shows that cycle exercise responses are strikingly different.
Central fatigue is the term used to describe when muscle contractions become limited by the abili... more Central fatigue is the term used to describe when muscle contractions become limited by the ability of the central nervous system to recruit motor neurones. Central fatigue becomes manifest when the effort is intense and is associated not only with reduced strength but also with an inability to maintain the contraction. The contractions thereby resemble those developed during partial neuromuscular blockade that mainly affect slow twitch muscle fibres. We suggest that central fatigue also manifests as a reduction in the ratio between the brain's uptake of oxygen relative to that of carbohydrate from 6 to less than 3. This imbalance between oxygen and glucose plus lactate uptake remains unsolved, but glycogen and accumulation of intermediates of metabolism are likely to play a key role.
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