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Alveolar oxygen uptake kinetics with step, impulse and ramp exercise in humans
No full textThe breath-by-breath V_ O2A of five male subjects
(21.2 years ±3.2; 78.8 kg ±5.9; 179.6 cm ±5.8) was
measured during a cycling exercise. Starting from a 10 W
baseline, the subjects performed (i) ON and OFF step
transitions (ST-ON; ST-OFF) to 50, 90, and 130 W; (ii) a
ramp (R) exercise with work rate gradually increasing by
20 W min1; (iii) impulse transitions (I) to 250 and
410 W lasting 10 and 5 s, respectively. The V_ O2A data
was modelled using non-linear weighted least square
regressions. The amplitudes of the V_ O2A response turned
out to be proportional to the input work rate intensities in
all the modalities of exercise. Time constants (s) and time
delays (td) of ST-ON and R responses were not significantly
different, whereas those of ST-OFF were characterised
by longer s values. s and td of I responses turned
out to be identical to those of ST-ON when the V_ O2A
responses were fitted using a five-component model.
These results suggest that: (i) the system controlling
alveolar gas exchange behaves linearly when it is forced
by ST and R inputs (the ON and OFF phases being
considered separate); (ii) the analysis of the I response
depends strongly on the models selected to fit the V_ O2A
data. The asymmetry between theONandOFF responses
mirrors that found between the splitting and resynthesis
rates of phosphocreatine, and these results support the
notion that phosphocreatine could be the main controller
of the skeletal muscle respiratory turnover in humans
Interplay among the changes of muscle strength, cross-sectional area and maximal explosive power: theory and facts
No full textA model has recently been proposed to predict the changes of mechanical power (Ẇ) during a maximal explosive effort (such as a standing high jump off both feet) following an adaptation (e.g. training/de-training). The model is based on the assumption that, all other things being equal (ceteris paribus), the predicted changes in Ẇ depend on the measured changes of muscle force (F) or cross-sectional area (CSA) only. It follows that, if the measured changes in Ẇ are not equal to those predicted by the model, factors other than a change in F (or CSA) must be responsible for this difference. The model does not allow the determination of factors specifically involved in the adaptation process but it helps in discriminating whether an adaptation has taken place at a local level (when the observed changes in F would be attributed to factors other than the observed changes in CSA, e.g. co-contractions, fibre type modifications...), or at a central level (when the observed changes in Ẇ would be attributed to other factors than the observed changes in F, e.g. co-ordination of multiple joints and muscle groups...), or in both regions. In this paper the model has been applied to data reported in the literature on disuse (BR, bed rest), de-conditioning (SF, space flight), strength training (ST) and de-training (DT). The results of these calculations have confirmed previous observations on the determinants of the adaptation process and further suggest: (1) that training for one specific motor task (e.g. ST) could affect the performance of a second task (e.g. a maximal explosive jump) but that, as soon as the trained motor task is terminated (DT), this ability is re-gained; and (2) that neuromuscular impairment in disuse (BR) is closer to de-training than to the de-conditioning brought about by weightlessness (SF)
Effects of different after-loads and muscular lengths on maximal explosive power of the lower limbs.
No full textMaximal explosive power during two-leg jumps was measured on four sedentary subjects [mean age 43.0 (SD 10.3) years, mean height 1.74 (SD 0.04) m, mean body mass 73.5 (SD 1.3) kg] using a sledge apparatus with which both force and speed could be directly measured. Different after-loads were obtained by positioning the sledge at five different angles (SA, alpha) in respect to the horizontal so that m . g . sin alpha (where m is the sum of body mass and the mass of the sledge seat, g the acceleration due to gravity) decreased (on average) from 78% body mass at 30 degrees to 27% body mass at 10 degrees, thus simulating conditions of low gravity. The subjects were asked to jump maximally, without counter movement, starting from 70 degrees, 90 degrees, 110 degrees, and 140 degrees of knee angle (KA); the protocol being repeated at 10 degrees, 15 degrees, 20 degrees, 25 degrees and 30 degrees SA. The average ((W) over dot(mean)(+)) power output during concentric exercise (CE) was found to decrease when the starting KA was increased, but to be unaffected by SA (i.e. by the after-load, the simulated low g). The higher values of (W) over dot(mean)(+) were recorded at 90 degrees KA [15.01 (SD 1.46) W . kg(-1), average for all subjects at all SA]. The subjects were also asked to perform counter movement (CMJ) and rebound jumps (RE) at the same SA as for CE. In CMJ and RE maximal power outputs were also found to be unaffected by the SA; (W) over dot(mean)(+) amounted to 16.03 (SD 0.28) W . kg(-1) in CMJ and 16.88 (SD 0.36) W . kg(-1) in RE (average for all subjects at all SA). In CE, CMJ and RE, the instantaneous force at the onset of the positive speed phase (F-i) was found to increase linearly with SA (i.e. with increasing m . g . sin alpha), and the difference between F-i in CMJ or RE and F-i in CE (F-i in CMJ minus F-i in CE and F-i in RE minus F-i in CE) was unaffected by SA. This indicated that both maximal power and the elastic recoil were unaffected by simulated low g ranging from 1.71 m . s(-2) (at 10 degrees SA) to 4.91 m . s(-2) (at 30 degrees SA)
Energetics of best performance in middle distance running.
No full textOxygen consumption (VO2) and blood lactate concentration were determined during constant-speed track running on 16 runners of intermediate level competing in middle distances (0.8-5.0 km). The energy cost of track running per unit distance (C(r)) was then obtained from the ratio of steady-state VO2, corrected for lactate production, to speed; it was found to be independent of speed, its overall mean being 3.72 +/- 0.24 J . kg-1 . m-1 (n = 58; 1 ml O2 = 20.9 J). Maximal VO2 (VO2max) was also measured on the same subjects. Theoretical record times were then calculated for each distance and subject and compared with actual seasonal.best performances as follows. The maximal metabolic power (E(rmax)) a subject can maintain in running is a known function of VO2max and maximal anaerobic capacity and of the effort duration to exhaustion (t(e)). E(rmax) was then calculated as a function of t(e) from VO2max, assuming a standard value for maximal anaerobic capacity. The metabolic power requirement (E(r)) necessary to cover a given distance (d) was calculated as a function of performance time (t) from the product C(r)dt-1 = E(r). The time values that solve the equality E(rmax) (t(e)) = E(r)(t), assumed to yield the theoretical best t, were obtained by an iterative procedure for any given subject and distance and compared with actual records. These calculations, applied to our data and to similar data obtained by Lacour et al. (Eur. J. Appl. Physiol. Occup. Physiol. 60: 38-43, 1990) on French elite athletes, show good agreement between actual and calculated best t values; their ratio was 1.078 +/- 0.095 (n = 41) and 1.026 +/- 0.0042 (n = 68), respectively, over distances from 800 to 5,000 m
Plasma cytokine changes in relation to exercise intensity and muscle damage
No full textThe purpose of this study was to compare the effects of exercise intensity and exercise-induced muscle damage on changes in anti-inflammatory cytokines and other inflammatory mediators. Nine well-trained male runners completed three different exercise trials on separate occasions: ( 1) level treadmill running at 60% VO2max (moderate-intensity trial) for 60 min; (2) level treadmill running at 85% VO2max (high-intensity trial) for 60 min; (3) downhill treadmill running ( - 10% gradient) at 60% VO2 max (downhill running trial) for 45 min. Blood was sampled before, immediately after and 1 h after exercise. Plasma was analyzed for interleukin-1 receptor antagonist (IL-1ra), IL-4, IL-5, IL-10, IL-12p40, IL-13, monocyte chemotactic protein-1 (MCP-1), prostaglandin E-2, leukotriene B-4 and heat shock protein 70 (HSP70). The plasma concentrations of IL-1ra, IL-12p40, MCP-1 and HSP70 increased significantly (P< 0.05) after all three trials. Plasma prostaglandin E-2 concentration increased significantly after the downhill running and high-intensity trials, while plasma IL-10 concentration increased significantly only after the high-intensity trial. IL-4 and leukotriene B4 did not increase significantly after exercise. Plasma IL-1ra and IL-10 concentrations were significantly higher ( P< 0.05) after the high-intensity trial than after both the moderate-intensity and downhill running trials. Therefore, following exercise up to 1 h duration, exercise intensity appears to have a greater effect on anti-inflammatory cytokine production than exercise-induced muscle damage
Optimising high-intensity treadmill training using the running speed at maximal O-2 uptake and the time for which this can be maintained
No full textThe aim of this study was to compare the effects of two high-intensity, treadmill interval-training programs on 3000-m and 5000-m running performance. Maximal oxygen uptake ((V) over dot O-2max), the running speed associated with (V) over dot O-2max (nu (V) over dot O-2max), the time for which nu (V) over dot O-2max can be maintained (T-max), running economy (RE), ventilatory threshold (VT) and 3000-m and 5000-m running times were determined in 27 well-trained runners. Subjects were then randomly assigned to three groups; (1) 60% T-max (2) 70% T-max and (3) control. Subjects in the control group continued their normal training and subjects in the two T-max groups undertook a 4-week treadmill interval-training program with the intensity set at nu (V) over dot O-2max and the interval duration at the assigned T-max. These subjects completed two interval-training sessions per week (60% T-max = six intervals/session, 70% T-max group = five intervals/session). Subjects were re-tested on all parameters at the completion of the training program. There was a significant improvement between pre- and post-training values in 3000-m time trial (TT) performance in the 60% T-max group compared to the 70% T,,a, and control groups [mean (SE); 60% T-max = 17.6 (3.5) s, 70% T-max = 6.3 (4.2) s, control = 0.5 (7.7) s]. There was no significant effect of the training program on 5000-m TT performance [60% T-max = 25.8 (13.8) s, 70% T-max = 3.7 (11.6) s, control = 9.9 (13.1) s]. Although there were no significant improvements in (V) over dot O-2max, nu (V) over dot (2max) and RE between groups, changes in (V) over dot O-2max and RE were significantly correlated with the improvement in the 3000-m TT. Furthermore, VT and T-max were significantly higher in the 60% Tmax group post-compared to pre-training. In conclusion, 3000-m running performance can be significantly improved in a group of well-trained runners, using a 4-week treadmill interval training program at nu (V) over dot O-2max with interval durations of 60% T-max
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