Kinetics of Phosphocreatine and Deoxyhemoglobin in Children and Adults During High-Intensity Exercise
Rebecca J. WillcocksAlan R. BarkerJonathan FulfordDeborah WelfordJoanne R. WelsmanNeil ArmstrongCraig A. Williams
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PURPOSE: To compare the kinetic response of PCr and deoxyhemoglobin (HHb) during high-intensity exercise in boys and men. METHODS: Seven men (25 ± 5 y) and six boys (13 ± 1 y) exercised using the right leg on a quadriceps ergometer within a 1.5 T MR scanner. Following habituation sessions each participant completed an incremental test to exhaustion. After a minimum 48 hours recovery, participants completed two to four constant work rate bouts on separate days. Exercise bouts consisted of 2 min rest and 7 min exercise, at an intensity equivalent to 20% of the difference between the workload at the intracellular Pi/PCr threshold and the maximal workload. Changes in HHb were determined every 1 s using a NIRS probe which was secured over the vastus lateralis muscle. 31P spectra were collected every 6 s using a 6 cm surface coil positioned beneath the right quadriceps muscle. The breakdown of PCr at the onset of exercise was modelled using a single-exponential function until the onset of the PCr slow component (SC). This point was identified using an iterative fitting window - where the time constant diverged from a plateau, a PCr SC was deemed to emerge. HHb profiles for participants were modelled as above, although a delay term was included in the model to account for the transient decrease in HHb at the onset of exercise. Data are reported as mean ± standard deviation and 95 % confidence intervals (CI) are presented. PCr and HHb data from two boys and HHb data from one adult were excluded from the analysis. RESULTS: The fundamental time constant (boys: 31 ± 11 s, CI 5 s; men: 45 ± 19 s, CI 6 s; P = 0.23), fundamental amplitude (boys: 43 ± 10%; men: 36 ± 8%, P = 0.24), and the SC amplitude (boys: 6 ± 1%; men: 12 ± 12%, P = 0.33) for PCr were similar in both groups. The net change in PCr was similar (men: 52 ± 16%; boys: 51 ± 9%, P = 0.93), as was the time constant for HHb increase in boys and men (19 ± 2 s and 22 ± 2 s, P = 0.55) respectively, with a delay of 5 ± 2 s. Responses over the last three minutes of exercise for HHB showed considerable inter-individual variation. CONCLUSIONS: Results from this study showed no differences in the breakdown of PCr or in the balance between the delivery and utilisation of O2 at the onset of highintensity exercise between boys and men. However, a trend of an age-related slowing of the breakdown of PCr at the onset of exercise warrants further investigation.Keywords:
Incremental exercise
Quadriceps muscle
Intensity
Spectral electromyographic (EMG) changes in human quadriceps muscles were studied to reinvestigate discrepant results concerning mean power frequency (MPF) changes during dynamic exercise. An incremental test consisting of a quasi-linear increase in mechanical power on a bicycle ergometer (for 20-100% of maximal aerobic power) was performed by forty subjects. During this test, surface EMGs from the quadriceps muscles showed that EMG total power (PEMG) increased with a curvilinear pattern for every subject, whereas MPF kinetics varied from one subject to another. PEMG changes had the same shape, which would lead to disappointing results in terms of discrimination between subjects. The ability of normalized MPF kinetics to define significant clusters of subjects was tested using a principal component analysis. This analysis led to the projection of all experiments onto a plane and revealed a relevant grouping of MPF profiles. Differences in MPF kinetics between clusters are interpreted in terms of various possibilities of balance between physiological events leading to an increase or a decrease in MPF.
Incremental exercise
Quadriceps muscle
Cycle ergometer
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Quadriceps muscle
Muscle relaxation
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Creatine
Creatine kinase
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Incremental exercise
High-energy phosphate
Exercise physiology
Adenosine triphosphate
Physical exercise
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Following intravenous administration of 32P-phosphocreatine (50 mg/kg) or an equimolar mixture of creatine + 32P-phosphate (equivalent to 50 mg/kg phosphocreatine) to rats, and examination of an extract of cardiac muscle by HPLC, the proportion of radiolabelled adenosine triphosphate (ATP; up to 3%) was similar in each treatment group at 120 min after dosing. Mean concentrations of ATP in the cardiac muscle were increased significantly during this time (to 3.1 mumol/g) after intravenous administration of 32P-phosphocreatine compared with those in control rats (2.5 mumol/g) and in rats dosed with creatine + 32P-phosphate mixture (2.6 mumol/g). Phosphocreatine concentrations in cardiac muscle of phosphocreatine-treated rats were also increased (2.3 mumol/g) significantly after 120 min compared with controls (1.7 mumol/g), but were unchanged after 30 min. Mean concentrations of phosphocreatine in rats receiving a creatine + phosphate mixture were slightly reduced (1.3 and 1.5 mumol/g after 30 min or 120 min, respectively) compared with controls. The elevation of tissue ATP and phosphocreatine levels may be involved in the protective effect provided by exogenous phosphocreatine against anoxia in isolated cardiac muscle.
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Adenosine triphosphate
Creatine kinase
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and EMG Activity Kinetics During Moderate and Severe Constant Work Rate Exercise in Trained Cyclists
The purpose of this study was to compare O(2) uptake ((.)VO(2)) and muscle electromyography activity kinetics during moderate and severe exercise to test the hypothesis of progressive recruitment of fast-twitch fibers in the explanation of the VO(2) slow component. After an incremental test to exhaustion, 7 trained cyclists (mean +/- SD, 61.4 +/- 4.2 ml x min(-1) x kg(- 1)) performed several square-wave transitions for 6 min at moderate and severe intensities on a bicycle ergometer. The (.)VO(2) response and the electrical activity (i.e., median power frequency, MDF) of the quadriceps vastus lateralis and vastus medialis of both lower limbs were measured continuously during exercise. After 2 to 3 min of exercise onset, MDF values increased similarly during moderate and severe exercise for almost all muscles whereas a (.)VO(2) slow component occurred during severe exercise. There was no relationship between the increase of MDF values and the magnitude of the (.)VO(2) slow component during the severe exercise. These results suggest that the origin of the slow component may not be due to the progressive recruitment of fast-twitch fibers.
Vastus medialis
Quadriceps muscle
Work rate
Incremental exercise
Vastus lateralis muscle
Bicycle ergometer
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1368 In skeletal muscle, phosphocreatine (PCr) recovery from submaximal exercise has become established as a reliable and accepted measure of muscle oxidative capacity. During exercise, oxygen availability plays a role in determining maximal oxidative metabolism, but the relationship between oxygenation and oxidative capacity measured by 31P magnetic resonance spectroscopy (MRS) during recovery from exercise has never been studied. Thus, we used 31P MRS to study exercising human gastrocnemius muscle under conditions of varied fractions of inspired oxygen (FIO2) to test the hypothesis that varied oxygen availability modulates PCr recovery from submaximal exercise. Six male subjects performed 3 bouts of 5 min steady state submaximal plantar flexion exercise followed by 5 min of recovery in a 1.5 Tesla magnet while breathing 3 different FIO2 (0.10, 0.21, and 1.00). Under each FIO2 treatment the PCr recovery time constants were significantly different, being longer in hypoxia (33.5 ± 4.1s) and shorter in hyperoxia (20.0 ± 1.8), than in normoxia (25.0 ± 2.7) (p ≤ 0.05) (mean ± SEM). End exercise pH was not significantly different between the 3 treatments while end exercise PCr levels tended to be lower with decreasing FIO2, but were not significant. These results demonstrate that PCr recovery is significantly altered by FIO2 and suggest that following submaximal exercise PCr recovery is dependent upon oxygen availability. Supported by NIH HL17731, AR40155, and Parker B. Francis Fellowship Program.
Hyperoxia
Gastrocnemius muscle
Oxidative metabolism
Incremental exercise
Exercise physiology
Hypoxia
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Two patients with mitochondrial encephalomyopathy due to complexes I and IV deficiencies received 150 mg/d of coenzyme Q10 (CoQ). We studied them with a bicycle ergometer exercise test and 31P NMR spectroscopy before and after 10 months of treatment. Before treatment, we observed a low phosphocreatine/inorganic phosphate (PCr/Pi) resting value along with abnormally high resting lactate concentration. During exercise, there was a pronounced acidosis with delayed kinetics of postexercise recovery for blood lactate, pH, PCr, and PCr/Pi ratio. Oxygen uptake during exercise was reduced while the lowering of the ventilatory threshold indicated an early activation of glycolysis. After treatment, the bicycle ergometer exercise test indicated a significant improvement with a decrease in resting blood lactate level, an increase in oxygen consumption during exercise, and an increase in the kinetics of lactate disappearance during the recovery period. A shift of the ventilatory threshold to higher workload was present. 31P NMR spectroscopy confirmed the improvement, showing a significant increase in the PCr/Pi ratio at rest and in the kinetics of recovery for pH, PCr, and PCr/Pi ratio following exercise in patient 1. For patient 2, we observed a less pronounced acidosis correlated with a lesser amount of Pi produced during exercise. These observations indicate an improvement of mitochondrial function and a shift from high to low glycolytic activity in both patients consequent to CoQ treatment.
Mitochondrial encephalomyopathy
Ventilatory threshold
Incremental exercise
Exercise physiology
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Using 31P-NMR technique it was shown that exogenous phosphocreatine (10 mM) added in the cardioplegic solution provided higher levels of recovery of intracellular ATP (approx. 60% vs. 26% in the control) and phosphocreatine (90% vs. 43%) in perfused rat hearts after 35 min of total ischemia. Simultaneously significantly higher levels of contractile recovery (90% vs. 35%) and a three-fold decrease in creatine kinase release into the perfusate were observed. These effects of exogenous phosphocreatine can be related to either intracellular action of this compound or its interaction with cellular membrane.
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Creatine kinase
Intracellular pH
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In skeletal muscle, phosphocreatine (PCr) recovery from submaximal exercise has become a reliable and accepted measure of muscle oxidative capacity. During exercise, O 2 availability plays a role in determining maximal oxidative metabolism, but the relationship between O 2 availability and oxidative metabolism measured by 31 P-magnetic resonance spectroscopy (MRS) during recovery from exercise has never been studied. We used 31 P-MRS to study exercising human gastrocnemius muscle under conditions of varied fractions of inspired O 2 [Formula: see text]) to test the hypothesis that varied O 2 availability modulates PCr recovery from submaximal exercise. Six male subjects performed three bouts of 5-min steady-state submaximal plantar flexion exercise followed by 5 min of recovery in a 1.5-T magnet while breathing three different[Formula: see text] concentrations (0.10, 0.21, and 1.00). Under each[Formula: see text] treatment, the PCr recovery time constants were significantly different, being longer in hypoxia [33.5 ± 4.1 s (SE)] and shorter in hyperoxia (20.0 ± 1.8 s) than in normoxia (25.0 ± 2.7 s) ( P ≤ 0.05). End-exercise pH was not significantly different among the three treatments (7.08 ± 0.01 for 0.10, 7.04 ± 0.01 for 0.21, and 7.04 ± 0.02 for 1.00). These results demonstrate that PCr recovery is significantly altered by[Formula: see text] and suggest that, after submaximal exercise, PCr recovery, under normoxic conditions, is limited by O 2 availability.
Oxidative metabolism
Exercise physiology
Hyperoxia
Incremental exercise
Gastrocnemius muscle
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