Muscle Phosphocreatine Kinetics Research Articles

Effects of small-volume soccer and vibration training on body composition, aerobic fitness, and muscular PCr kinetics for inactive women aged 20–45

PurposeThe present study investigated the effects of 16 weeks of small-volume, small-sided soccer training soccer group (SG, n = 13) and oscillating whole-body vibration training vibration group (VG, n = 17) on body composition, aerobic fitness, and muscle PCr kinetics in healthy inactive premenopausal women in comparison with an inactive control group (CO, n = 14). MethodsTraining for SG and VG consisted of twice-weekly 15-min sessions with average heart rates (HRs) of ∼155 and 90 bpm respectively. Pre- and post-measurements of body composition (DXA), phosphocreatine (PCr) on- and off-kinetics, and HR measurements during standardised submaximal exercise were performed. ResultsAfter 16 weeks of training in SG, fat percentage was lowered (p = 0.03) by 1.7% ± 2.4% from 37.5% ± 6.9% to 35.8% ± 6.2% and the PCr decrease in the quadriceps during knee-extension ramp exercise was attenuated (4% ± 8%, p = 0.04), with no changes in VG or CO (time-group effect: p = 0.03 and p = 0.03). Submaximal exercise HR was also reduced in SG after 16 weeks of training (6% ± 5% of HRmax, p = 0.01). ConclusionShort duration soccer training for 16 weeks appears to be sufficient to induce favourable changes in body composition and indicators of aerobic fitness and muscle oxidative capacity in untrained premenopausal women.

Commentaries on Viewpoint: Do oxidative and anaerobic energy production in exercising muscle change throughout growth and maturation?

Commentaries on Viewpoint: Do oxidative and anaerobic energy production in exercising muscle change throughout growth and maturation?

Muscle Phosphocreatine Kinetics In Children And Adults During High-intensity Exercise

PURPOSE: To compare the age and sex differences in the kinetic response of muscle PCr during high-intensity exercise in children and adults. METHODS: Eleven adults (6 men 25 ± 5 y and 5 women 23 ± 3 y) and 11 children (6 boys 13 ± 0.2 y and 5 girls 13 ±1.3 y) exercised using their right leg on a quadriceps ergometer within a 1.5 Tesla MR scanner. Following habituation, 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. 31P spectra were collected every 6 s using a 6 cm surface coil positioned beneath the right quadriceps muscle. The breakdown of muscle 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. Data are reported as mean ± standard deviation and 95% confidence intervals (CI) are presented. A two by two factorial ANOVA was utilised to determine group differences. RESULTS: No significant interaction effect was found for the fundamental time constant (boys: 31 ± 10, CI 5; girls: 31 ± 10, CI 6; men: 44 ± 20, CI 6; women: 29 ± 14 s, CI 6 s; P=0.26), or the fundamental amplitude (boys: -39 ± 10; girls: -42 ± 9; men: -36 ± 9; women: -48 ± 9%; P=0.23), or the SC PCr (as a % of the difference between the fundamental amplitude and end exercise PCr) which was similar across groups (boys: 6 ± 1; girls: 13 ± 8; men: 8 ± 5; women: 8 ± 6% P=0.15). The end-exercise PCr revealed a significant sex difference (P=0.03) but no significant age or interaction effect (boys: 55 ± 10; girls: 46 ± 14; men: 56 ± 11; women: 44 ± 8%). There was no significant difference between age (P=0.22) or sex (P=0.13) for the PCr cost of contraction at end-exercise (boys: 1.7 ± 0.5; girls: 1.3 ± 0.5; men: 1.4 ± 0.4; women: 1.2 ± 0.2 mM·W-1P=0.13). CONCLUSION: The kinetics of muscle PCr during high intensity exercise are similar in 13 y old children and adults, suggesting the phosphate-linked control of oxidative metabolism, at least during high-intensity exercise, is adult like by this age.

Influence of dietary creatine supplementation on muscle phosphocreatine kinetics during knee-extensor exercise in humans

We hypothesized that increasing skeletal muscle total creatine (Cr) content through dietary Cr supplementation would result in slower muscle phosphocreatine concentration ([PCr]) kinetics, as assessed using (31)P magnetic resonance spectroscopy, following the onset and offset of both moderate-intensity (Mod) and heavy-intensity (Hvy) exercise. Seven healthy males (age 29 +/- 6 yr, mean +/- SD) completed a series of square-wave transitions to Mod and Hvy knee extensor exercise inside the bore of a 1.5-T superconducting magnet both before and after a 5-day period of Cr loading (4x 5 g/day of creatine monohydrate). Cr supplementation resulted in an approximately 8% increase in the resting muscle [PCr]-to-[ATP] ratio (4.66 +/- 0.27 vs. 5.04 +/- 0.22; P < 0.05), consistent with a significant increase in muscle total Cr content consequent to the intervention. The time constant for muscle [PCr] kinetics was increased following Cr loading for Mod exercise (control: 15 +/- 8 vs. Cr: 25 +/- 9 s; P < 0.05) and subsequent recovery (control: 14 +/- 8 vs. Cr: 27 +/- 8 s; P < 0.05) and for Hvy exercise (control: 54 +/- 18 vs. Cr: 72 +/- 30 s; P < 0.05), but not for subsequent recovery (control: 41 +/- 11 vs. Cr: 44 +/- 6 s). The magnitude of the increase in [PCr] following Cr loading was correlated (P < 0.05) with the extent of the slowing of the [PCr] kinetics for the moderate off-transient (r = 0.92) and the heavy on-transient (r = 0.71). These data demonstrate, for the first time in humans, that an increase in muscle [PCr] results in a slowing of [PCr] dynamics in exercise and subsequent recovery.

Interpreting the phosphocreatine time constant in aerobically exercising skeletal muscle

to the editor: Francescato et al. ([1][1]) contrast the lack of interindividual correlation between the phosphocreatine (PCr) time constant (τPCr) and the ADP concentration ([ADP]) change from rest to steady state (Δ[ADP]S) during moderate aerobic exercise with the fact that “…ADP

Muscle phosphocreatine kinetics in children and adults at the onset and offset of moderate-intensity exercise

The splitting of muscle phosphocreatine (PCr) plays an integral role in the regulation of muscle O2 utilization during a "step" change in metabolic rate. This study tested the hypothesis that the kinetics of muscle PCr would be faster in children compared with adults both at the onset and offset of moderate-intensity exercise, in concert with the previous demonstration of faster phase II pulmonary O2 uptake kinetics in children. Eighteen peri-pubertal children (8 boys, 10 girls) and 16 adults (8 men, 8 women) completed repeated constant work-rate exercise transitions corresponding to 80% of the Pi/PCr intracellular threshold. The changes in quadriceps [PCr], [Pi], [ADP], and pH were determined every 6 s using 31P-magnetic resonance spectroscopy. No significant (P>0.05) age- or sex-related differences were found in the PCr kinetic time constant at the onset (boys, 21+/-4 s; girls, 24+/-5 s; men, 26+/-9 s; women, 24+/-7 s) or offset (boys, 26+/-5 s; girls, 29+/-7 s; men, 23+/-9 s; women 29+/-7 s) of exercise. Likewise, the estimated theoretical maximal rate of oxidative phosphorylation (Qmax) was independent of age and sex (boys, 1.39+/-0.20 mM/s; girls, 1.32+/-0.32 mM/s; men, 2.36+/-1.18 mM/s; women, 1.51+/-0.53 mM/s). These results are consistent with the notion that the putative phosphate-linked regulation of muscle O2 utilization is fully mature in peri-pubertal children, which may be attributable to a comparable capacity for mitochondrial oxidative phosphorylation in child and adult muscle.

Linear dependence of muscle phosphocreatine kinetics on oxidative capacity.

The influence of muscle oxidative capacity on phosphocreatine (PCr) changes during and after stimulation was examined in the superficial (fast-twitch) section of rat gastrocnemius muscles. Muscle mitochondrial enzymes were increased in one group of rats by 8-10 wk of training on a running wheel (to a final regimen of 50 min/day at 38 m/min, 5 days/wk) and decreased in another group by chemical thyroidectomy [0.025% methimazole (MMI) in drinking water for 8 wk]. After these treatments, muscle citrate synthase activity was 179 and 29%, respectively, of that in corresponding control groups. Muscle PCr and pH were measured by 31P-nuclear magnetic resonance spectroscopy before, during, and after 8 min of isometric twitch stimulation at 0.33 Hz (MMI) or 0.75 Hz (trained) and 2 Hz. There was a significant linear correlation (r = 0.84, P < 0.01) between the rate constant for PCr recovery after submaximal stimulation (0.33 or 0.75 Hz) and citrate synthase activity. Within the control groups, there was a significant correlation (r = 0.72, P < 0.01) between the rate constant for PCr recovery and intracellular pH at the end of stimulation. The results are quantitatively consistent with linear/quasilinear models of respiratory control by the cytoplasmic free energy of ATP hydrolysis but not with respiratory control by cytoplasmic ADP.

Linear dependence of muscle phosphocreatine kinetics on total creatine content.

Phosphorus nuclear magnetic resonance (NMR) spectra and twitch tension were recorded during stimulation of gastrocnemius muscles of pentobarbital sodium-anesthetized rats which had been fed the creatine analogue beta-guanidinopropionic acid (beta-GPA, 2% diet) for periods from 0 (control) to 8 wk. Total creatine content of unstimulated muscles decreased by 42, 67, 82, and 88% compared with controls after 2-, 4-, 6-, and 8-wk feeding, respectively. The staircase effect observed in control muscles during 8 min of twitch stimulation at 0.25, 0.5, and 0.75 Hz was reduced after 2- to 8-wk beta-GPA feeding. However, after 6- to 8-wk feeding, the twitch force at the end of 8 min of stimulation was not different from controls. The time constant for phosphocreatine (PCr) changes at the onset of and during recovery after stimulation was proportional to total creatine content. The relationship between PCr content and twitch rate times force at the end of stimulation was linear, with slope proportional to total creatine content. PCr content in beta-GPA-fed animals was transiently greater during recovery than before stimulation, suggesting a regulatory effect of the inorganic phosphate released by hydrolysis of phosphorylated beta-GPA. The results are consistent with linear models of respiratory control in which the creatine kinase reaction acts as a simple buffer of adenine nucleotide levels.

When is it justified to stop the pill?

<h3>Aim</h3> To provide an evidence-based review of muscle metabolism changes with sex-, age- and maturation with reference to the development of youth sport performance. <h3>Methods</h3> A narrative review of data from both invasive and non-invasive studies, from 1970 to 2015, founded on personal databases supported with computer searches of PubMed and Google Scholar. <h3>Results</h3> Youth sport performance is underpinned by sex-, age- and maturation-related changes in muscle metabolism. Investigations of muscle size, structure and metabolism; substrate utilisation; pulmonary oxygen uptake kinetics; muscle phosphocreatine kinetics; peak anaerobic and aerobic performance; and fatigue resistance; determined using a range of conventional and emerging techniques present a consistent picture. Age-related changes have been consistently documented but specific and independent maturation-related effects on muscle metabolism during exercise have proved elusive to establish. Children are better equipped for exercise supported primarily by oxidative metabolism than by anaerobic metabolism. Sexual dimorphism is apparent in several physiological variables underpinning youth sport performance. As young people mature there is a progressive but asynchronous transition into an adult metabolic profile. <h3>Conclusions</h3> The application of recent developments in technology to the laboratory study of the exercising child and adolescent has both supplemented existing knowledge and provided novel insights into developmental exercise physiology. A sound foundation of laboratory-based knowledge has been established but the lack of rigorously designed child-specific and sport-specific testing environments has clouded the interpretation of the data in real life situations. The primary challenge remains the translation of laboratory research into the optimisation of youth sports participation and performance.