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.
The multi-stage fitness test (MSFT) is a widely used exercise test to predict maximal oxygen uptake (VO2max) and to give an indication of aerobic fitness and in both adults and children. However it has been shown to under predict VO2max in adults when compared to actual values measured in the laboratory (Stickland et al., 2003) and measured directly during a MSFT (Kilding et al., 2006). PURPOSE: To directly measure oxygen uptake during a MSFT to determine the validity of this test for predicting VO2max in prepubertal boys. METHODS: Eleven boys aged 12.2 ± 0.4 years; body mass, 45.5 ± 8.0 kg; and height, 154.2 ± 6.6 cm participated in this study. The maturity of each child was determined by using the equation provided by Mirwald et al. (2002) to give an estimate of years from peak height velocity. The MSFT was carried out indoors and was performed individually whilst wearing a portable gas analyser and heart rate monitor. Participants completed as many 20 metre shuttle runs as possible in response to an audible cue. Values for oxygen uptake were averaged over 30 second periods and the highest recorded oxygen uptake was accepted as VO2max. Predicted VO2max was calculated using the table provided by Ramsbottom et al. (1988) and from age and maximal speed in the MSFT (Leger et al. 1988). Data was analysed using paired t-tests. RESULTS: The calculation of maturity showed a mean of 1.18 years from peak height velocity. Predicted values for VO2max were significantly lower than measured values (36.3 ml.kg-1.min-1 vs. 49.0 ml.kg-1.min-1; p< 0.001) when calculated using the table provided by Ramsbottom et al. (1988). There was no significant difference between predicted values for VO2maxcalculated using age and maximal speed (Leger et al. 1988) and the measured values (45.2 ml.kg-1.min-1 vs. 49.0 ml.kg-1.min-1; p>0.05). CONCLUSIONS: This is the first study to directly measure maximal oxygen uptake during a MSFT in children. It has shown that the MSFT can be valid method of predicting VO2max in prepubertal boys but that this is dependant on using paediatric specifice prediction methods.
PURPOSE: To examine whether the kinetics of muscle phosphocreatine and deoxygentation at the onset of moderate intensity quadriceps exercise are age and/or sex dependent. METHODS: Twelve 9-10 y old children (7 boys, 5 girls) and 15 young adults (8 men, 7 women) completed repeat constant work-rate exercise transitions (2 min rest, 6 min exercise) corresponding to 80% of the Pi/PCr intracellular threshold on a single legged quadriceps ergometer whilst lying prone inside an MR scanner (1.5T). Quadriceps changes in muscle PCr were determined every 6 s using 31P-magnetic resonance spectroscopy, whereas deoxyhemoglobin (Hb) dynamics were determined every 1 s from the vastus lateralis muscle using near infrared spectroscopy. The PCr kinetic parameters were estimated using a single-exponential model with no delay term, whereas a singleexponential model including a delay term was used for the Hb response. RESULTS: No significant (P >0.05) age or sex related differences were found for the PCr kinetic time constant at the onset of exercise (boys, 21 ± 4; girls, 24 ± 3; men, 26 ± 9; women, 24 ± 7 s). The 95% confidence intervals were ~ ±5 s for all PCr time constants. Likewise, no age or sex related differences were present for the Hb delay term (boys, 10 ± 7; girls, 9 ± 4; men, 16 ± 11; women, 30 ± 25 s), the Hb time constant (boys, 18 ± 14; girls, 17 ± 5; men, 27 ± 10; women, 25 ± 9 s) and the Hb mean response time (boys, 28 ± 22; girls, 25 ± 5; men, 41 ± 18; women, 55 ± 31 s) at the onset of exercise. However, a significant main effect for age did reveal a shorter Hb delay time (10 vs. 22 s, P = 0.009), a faster Hb time constant (18 vs. 26 s, P = 0.042) and a more rapid Hb mean response time (27 vs. 48 s, P = 0.006) in the children compared to the adults respectively. CONCLUSION: The kinetics of muscle PCr are independent of age and sex during the transition to moderate intensity quadriceps exercise. However, further work is required to explore a potential age-related modulation of the Hb dynamics, which may reflect an earlier imbalance between muscle O2 delivery and utilisation in children following the onset of moderate exercise.
This study tested the hypothesis that the muscle metabolic responses of 9- to 12-yr-old children and young adults during incremental quadriceps exercise are dependent on age and sex.Fifteen boys, 18 girls, 8 men, and 8 women completed a quadriceps step-incremental test to exhaustion inside a magnetic resonance scanner for determination of the muscle metabolic responses using P-magnetic resonance spectroscopy. Quadriceps muscle mass was determined using magnetic resonance imaging scans enabling comparison of metabolic data at a normalized power output.The power output and the energetic state at the Pi/PCr and pH intracellular thresholds (IT) were independent of age and sex. The rate of change in Pi/PCr against power output after the ITPi/PCr (S2) was lower in boys (0.158 +/- 0.089) and girls (0.257 +/- 0.110) compared with men (0.401 +/- 0.114, P < 0.001) and women (0.391 +/- 0.133, P = 0.014), respectively, with sex differences present for children only (P = 0.003). Above the ITpH, S2 was more rapid in the men (-0.041 +/- 0.022, P = 0.003) and girls (-0.030 +/- 0.013, P = 0.011) compared with boys (-0.019 +/- 0.007), with no differences between the girls and the women (-0.035 +/- 0.015, P = 0.479). The increase in Pi/PCr at exhaustion was lower in boys (0.85 +/- 0.38) than that in men (1.86 +/- 0.65, P < 0.001) and in girls (1.78 +/- 1.25) than that in women (4.97 +/- 3.52, P = 0.003), with sex differences in both the child (P = 0.005) and the adult groups (P = 0.019).During moderate-intensity exercise, muscle metabolism appears adult-like in 9- to 12-yr-old children, although both age- and sex-related differences in the "anaerobic" energy turnover are present during high-intensity exercise.
3rd ESTRO Forum 2015 S703 first, third and fourth treatment sessions.Heat with mobile insulator sheets was used during the second and fourth treatment sessions.The mobile insulator sheets comprised silicon rubber of 1.0 mm in thickness, which covered 75% of the surface of both the electrodes.The sheets were alternately arranged and moved in parallel at certain intervals.The intra-rectal temperature was measured using a four-point microthermocouple sensor during the heating.Several thermal parameters between the sessions with and without the mobile insulator sheets were evaluated.Results: Ten patients with pelvic tumors (eight cases of prostate cancer, two cases of cervical cancer of the uterus) were eligible for the study.All 10 patients could receive the planned five HT sessions.A planned heating time of 50 minutes was completed in 15 (75%) of 20 HT sessions with mobile insulator sheets and in 25 (83%) of 30 HT sessions without them.A thermal parameter of the cumulative equivalent minutes at 43ºC for the T90 (CEM43 ºCT90) was 1.9 minutes during the HT sessions with mobile insulator sheets and 1.2 minutes during the HT sessions without them, and this difference was statistically significant (p<0.05).The median minimum intra-rectal temperature (Tmin) was 40.8ºC during HT sessions with mobile insulator sheets and 40.6ºC during HT sessions without them, which was also a significant difference (p<0.05).Conclusions: This clinical prospective study demonstrated that the novel deep heating method using an 8 MHz radiofrequency-capacitive heating device with the mobile insulator sheets could improve the temperature increase of deep-seated tumors of the pelvis.
This study aimed to characterize changes in deoxyhemoglobin ([HHb]) response dynamics in boys and girls during ramp incremental exercise to investigate whether the reduced peak oxygen uptake (peak V˙O2) in girls is associated with poorer matching of muscle O2 delivery to muscle O2 utilization, as evidenced by a more rapid increase in [HHb].Fifty-two children (31 boys, 9.9 ± 0.6 yr, 1.38 ± 0.07 m, 31.70 ± 5.78 kg) completed ramp incremental exercise on a cycle ergometer during which pulmonary gas exchange and muscle oxygenation parameters were measured.When muscle [HHb] was expressed against absolute work rate and V˙O2, girls had an earlier change in [HHb], as evidenced by the lower c/d parameter (girls, 54 ± 20 W, vs boys, 67 ± 19 W, P = 0.023; girls, 0.82 ± 0.28 L·min(-1), vs boys, 0.95 ± 0.19 L·min(-1), P = 0.055) and plateau (girls, 85 ± 12 W, vs boys, 99 ± 18 W, P = 0.031; girls, 1.02 ± 0.25 L·min(-1), vs boys, 1.22 ± 0.28 L·min(-1), P = 0.014). However, when expressed against relative work rate or V˙O2, there were no sex differences in ([HHb]) response dynamics (all P > 0.20). Significant correlations were observed between absolute and fat-free mass normalized peak V˙O2 and the HHb c/d and plateau parameters when expressed against absolute work rate or V˙O2. Furthermore, when entered into a multiple regression model, the [HHb] plateau against absolute V˙O2 contributed 12% of the variance in peak V˙O2 after adjusting for fat-free mass, gas exchange threshold, and body fatness (model R2 = 0.81, P < 0.001).The sex difference in peak V˙O2 in 9- to 10-yr-old children is, in part, related to sex-specific changes in muscle O2 extraction dynamics during incremental exercise.
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