Influence of initial metabolic rate on the power–duration relationship for all-out exercise

A single 3-min all-out cycling test can be used to estimate the power asymptote (critical power, CP) and the curvature constant (W') of the power-duration relationship for severe-intensity exercise. It was hypothesized that when exercise immediately preceding the 3-min all-out test was performed CP would systematically reduce the W' without affecting the CP. Seven physically active males completed 3-min all-out cycling tests in randomized order immediately preceded by: unloaded cycling (control); 6-min moderate; 6-min heavy; 2-min severe (S2); or 4-min severe (S4) intensity exercise. The CP was estimated from the mean power output over the final 30 s of the test and the W' was estimated as the power-time integral above end-test power. There were no significant differences in the CP between control (279 ± 62), moderate (275 ± 52), heavy (286 ± 66 W), S2 (274 ± 55), or S4 (273 ± 65 W). The W' was significantly lower (P < 0.05) in S2 (11.5 ± 2.5) and S4 (8.9 ± 2.2) than in control (16.3 ± 2.3), moderate (17.2 ± 2.4) and heavy (15.6 ± 2.3 kJ). These results support the notion that the W' is predictably depleted only at a power output >CP whereas the CP is independent of the mechanisms which reduce W'.     

Influence of muscle architecture on the torque and power–velocity characteristics of young and elderly men

This study investigated the contribution of muscle architecture to the differences in the torque–velocity and power–velocity relationships between older (OM n = 9, aged 69–82 years) and younger men (YM n = 15, aged 19–35 years). Plantarflexors’ (PF) maximal isometric and concentric torques were recorded at 0.87, 1.75, 2.62, 3.49 and 4.36 rad s⁻¹. Physiological cross-sectional area (PCSA) was calculated as the ratio of muscle volume (determined by magnetic resonance imaging) to muscle fascicle length (L _f, measured by ultrasonography). GM PCSA and L _f of the OM were, respectively, 14.3% (P < 0.05) and 19.3% (P < 0.05) smaller than of the YM. In the OM, GM maximum isometric torque and maximum contraction velocity (V _max), estimated from Hill’s equation were, respectively, 48.5 and 38.2% lower (P < 0.001) than in the YM. At all contraction velocities, the OM produced less torque than the YM (46.3% of YM at 0.87 rad s⁻¹ to 14.7% at 4.36 rad s⁻¹, P < 0.001). Peak power (PP) of the OM was 80% lower than that of the YM and normalisation of PP to muscle volume only reduced this difference by 10%. Normalisation of torque to PCSA reduced, but did not eliminate, differences in torque between YM and OM (9.6%) and differences in torque/PCSA increased with contraction velocity (P < 0.05). After normalisation of velocity to L _f, the difference in V _max between the OM and the YM was reduced to 15.9%. Thus, although muscle architecture contributes significantly to the differences in the torque– and power–velocity properties of OM and YM, other contractile factors, intrinsic to the muscle, seem to play a role. It is noteworthy that the deficit in PP between OM and YM is far greater than that of muscle torque, even after normalisation of PP to muscle volume. This finding likely plays an important role in the loss of mobility in old age.     

Effects of crank length on maximal cycling power and optimal pedaling rate of boys aged 8–11 years

It is generally reported that cycle crank length affects maximal cycling power of adults and that optimal crank length is related to leg length. This suggests that the use of standard length cycle cranks may provide non-optimal test conditions for children. The purpose of this study was to determine the effects of cycle-crank length on maximal cycling power and optimal pedaling rate of 17 boys aged 8–11 years. The boys performed maximal cycle ergometry with standard (170 mm) cycle cranks and with a crank length that was 20% of estimated leg length (LL20). Power produced when using the 170 mm cranks [mean (SEM)] [364 (18) W] did not differ from that produced with the LL20 cranks [366 (19)]. Optimal pedaling rate was significantly greater for the LL20 cranks [129 (4) rpm] than for the 170 mm cranks [114 (4) rpm]. These data suggest that standard 170 mm cranks do not compromise maximal power measurements in boys aged 8–11 years so that the test apparatus does not bias physiological or developmental inferences made from tests of maximal cycling power. Electronic Publication     

Influence of chronic food deprivation on structure–function relationship of juvenile rat fast muscles

In the present study, we analyze the influence of chronic undernutrition on protein expression, muscle fiber type composition, and fatigue resistance of the fast extensor digitorum longus (EDL) muscle of male juvenile rats (45 ± 3 days of life; n = 25 and 31 rats for control and undernourished groups, respectively). Using 2D gel electrophoresis and mass spectrometry, we identified in undernourished muscles 12 proteins up-regulated (8 proteins of the electron transport chain and the glycolytic pathway, 2 cross-bridge proteins, chaperone and signaling proteins that are related to the stress response). In contrast, one down-regulated protein related to the fast muscle contractile system and two other proteins with no changes in expression were used as charge controls. By means of COX and alkaline ATPase histochemical techniques and low-frequency fatigue protocols we determined that undernourished muscles showed a larger proportion (15 % increase) of Type IIa/IId fibers (oxidative-glycolytic) at the expense of Type IIb (glycolytic) fibers (15.5 % decrease) and increased fatigue resistance (55.3 %). In addition, all fiber types showed a significant reduction in their cross-sectional area (slow: 64.4 %; intermediate: 63.9 % and fast: 61.2 %). These results indicate that undernourished EDL muscles exhibit an increased expression of energy metabolic and myofibrillar proteins which are associated with the predominance of oxidative and Type IIa/IId fibers and to a higher resistance to fatigue. We propose that such alterations may act as protective and/or adaptive mechanisms that counterbalance the effect of chronic undernourishment.     

Effect of countermovement on power–force–velocity profile

Purpose

To study the effect of a countermovement on the lower limb force–velocity (F–v) mechanical profile and to experimentally test the influence of F–v mechanical profile on countermovement jump (CMJ) performance, independently from the effect of maximal power output (P _max).

Methods

Fifty-four high-level sprinters and jumpers performed vertical maximal CMJ and squat jump (SJ) against five to eight additional loads ranging from 17 to 87 kg. Vertical ground reaction force data were recorded (1,000 Hz) and used to compute center of mass vertical displacement. For each condition, mean force, velocity, and power output were determined over the entire push-off phase of the best trial, and used to determine individual linear F–v relationships and P _max. From a previously validated biomechanical model, the optimal F–v profile maximizing jumping performance was determined for each subject and used to compute the individual mechanical F–v imbalance (Fv _IMB) as the difference between actual and optimal F–v profiles.

Results

A multiple regression analysis clearly showed (r ² = 0.952, P < 0.001, SEE 0.011 m) that P _max, Fv _IMB and lower limb extension range (h _PO) explained a significant part of the interindividual differences in CMJ performance (P < 0.001) with positive regression coefficients for P _max and h _PO and a negative one for Fv _IMB.

Conclusion

Compared to SJ, F–v relationships were shifted to the right in CMJ, with higher P _max, maximal theoretical force and velocity (+35.8, 20.6 and 13.3 %, respectively). As in SJ, CMJ performance depends on Fv _IMB, independently from the effect of P _max, with the existence of an individual optimal F–v profile (Fv _IMB having an even larger influence in CMJ).     

Changes in R–R variability before and after endurance training measured by power spectral analysis and by the effect of isometric muscle contraction

The long-term conditioning effects of physical training on cardiorespiratory interaction in 11 young healthy males were studied. Significant increases in maximum oxygen uptake ( )(P < 0.05) and decreases in heart rate (P < 0.05) were achieved in all subjects following a 6-week training programme consisting of cycling for 25 min each day at a work level that increased heart rate to 85% of maximum. Heart rate variability, measured as the differences between the maximum and minimum R-R interval in a respiratory cycle, increased in nine of the subjects and decreased in two. The respiratory-cycle-related high-frequency peak in the power spectral plot of R-R variability also showed significant increases in the same nine subjects and decreases in two. The latter result was similar after normalisation of the data for changes in heart rate by calculating the common coefficient of variance ( ), where HF is the high-frequency component of the power spectral plots, using a further measure of vagal tone it was shown that, for all subjects, the R-R interval change in response to isometric contractions of the arm flexors in one respiratory cycle were significantly greater after training. These data suggest that cardiac vagal tone is increased by aerobic training for all subjects and that this is accompanied by a respiratory sinus arrhythmia (RSA) in most, but may be associated with a decrease in RSA in subjects with a very low ( < 50 beats-min⁻¹ heart rate.     

Effects of S-glutathionylation on the passive force–length relationship in skeletal muscle fibres of rats and humans

Journal of Muscle Research and Cell Motility - This study investigated the effect of S-glutathionylation on passive force in skeletal muscle fibres, to determine whether activity-related redox...     

Influence of age,body temperature,GABAA receptor inhibition and caffeine on the Hering–Breuer inflation reflex in unanesthetized rat pups

We measured the duration of apnea induced by sustained end-inspiratory lung inflation (the Hering Breuer Reflex, HBR) in unanesthetized infant rat pups aged 4 days (P4) to P20 at body temperatures of 32 °C and 36 °C. The expiratory prolongation elicited by the HBR lasted longer in the younger pups and lasted longer at the higher body temperature. Blockade of adenosine receptors by caffeine following injection into the cisterna magna (ICM) significantly blunted the thermal prolongation of the HBR. Blockade of gama-amino-butyric acid A (GABA_A) receptors by pre-treatment with ICM bicuculline had no effect on the HBR duration at either body temperature. To test the hypothesis that developmental maturation of GABAergic inhibition of breathing was modifying the response to bicuculline, we pretreated rat pups with systemically administered bumetanide to lower the intracellular chloride concentration, and repeated the bicuculline studies. Bicuculline still did not alter the HBR at either temperature after bumetanide treatment. We administered PSB-36, a selective adenosine A1 receptor antagonist, and this drug treatment did not modify the HBR. We conclude that caffeine blunts the thermal prolongation of the HBR, probably by blocking adenosine A2a receptors. The thermally sensitive adenosinergic prolongation of the HBR in these intact animals does not seem to depend on GABA_A receptors.     

Physiological studies on trematodes — surface area — body weight relationship in Cotylophoron Cotylophoron and Gastrothylax Crumenifer

Summary 1. The surface area body weight relationship in C. cotylophoron and G. crumenifer has been determined.2. The relationship between surface area and body weight in C. cotylophoron was found to be governed by Y=14.67 (W ₁)^0.70 and Y=6.99 (W ₂)^0.68 and in G. crumenifer Y=7.50 (W ₁)^0.70 and Y=4.30 (W ₂)^0.76, where Y represents the surface area in sq. mm, W ₁ and W ₂ for dry and fresh weights in mg respectively.

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Zusammenfassung 1. Bei C. cotylophoron und G. crumenifer wird das Verhältnis der Oberfläche zum Körpergewicht bestimmt.2. Die Beziehung zwischen Körperoberfläche und Körpergewicht liegt bei C. cotylophoron bei etwa Y=14,67 (W ₁)^0,70 und Y=6,99 (W ₂)^0,68 und bei G. crumenifer Y=7,50 (W ₁)^0,70 und Y=4,30 (W ₂)^0,76, wo die Oberflächen in mm², W ₁ und W ₂ das Trocken- und Frischgewicht in mm angeben.

     

Influence of the sample collection method on salivary interleukin–6 levels in resting and post-exercise conditions

Previous studies demonstrated that no significant relationships exist between salivary and serum IL-6 in resting conditions and following exercise and that appropriate saliva collection procedures allow to avoid analytical drawbacks. This investigation aimed to: (a) compare the effects of two methods of saliva collection on IL-6 assay; (b) search for correlation between salivary and serum IL-6 in resting and post-exercise conditions; (c) evaluate the IL-6 response to isometric contractions. Seventeen sedentary subjects and fifteen athletes underwent one blood and two salivary draws: saliva was collected chewing on cotton salivettes and using a plastic straw (SA method and ST method, respectively). Afterwards, the athletes only completed a fatiguing isometric exercise of the knee extensors and blood and saliva were sampled after the exercise. In the entire group (n = 32), ST method produced higher IL-6 levels than SA method and serum sampling. The exercise elicited significant responses of lactate, serum IL-6, salivary IL-6 (by ST method): salivary IL-6 values using the ST collection method were higher at each sampling point than with the SA method. The correlation analyses applied to both resting levels in the entire group and absolute changes above baseline in the athlete group showed that: (1) no significant relationships exist between serum and salivary IL-6 levels; (2) the greater the salivary IL-6 measurement, the higher the resultant inaccuracy of the SA method; (3) significant correlations exist between isometric force and mechanical fatigue during exercise and peaks of lactate and serum IL-6. These data provided demonstration of a cotton-interference effect for the results of salivary IL-6 assay and confirmed the lack of significant correlation between salivary and serum IL-6 in resting and post-exercise conditions.     

Influence of “living high–training low” on aerobic performance and economy of work in elite athletes

This study tested the effects of “living high-training low” (Hi–Lo) on aerobic performance and economy of work in elite athletes. Forty endurance athletes (cross-country skiers, swimmers, runners) performed 13–18 consecutive days of training at 1,200 m altitude, by sleeping at 1,200 m (LL, n = 20) or in hypoxic rooms with 5–6 nights at 2,500 m followed by 8–12 nights at 3,000–3,500 m (HL, n = 20). The athletes were evaluated before (pre-), one (post-1) and 15 days (post-15) after Hi–Lo. Economy was assessed from two sub-maximal tests, one non-specific (cycling) and one specific (running or swimming). From pre- to post-1: increased both in HL (+ 7.8%, P < 0.01) and in LL (+ 3.3%, P < 0.05), peak power output (PPO) tended to increase more (P=0.06) in HL (+ 4.1%, P < 0.01) than in LL (+ 1.9%). At post-15, has returned to pre-values in both groups, PPO increased more (P < 0.05) in HL (+ 8.3%, P < 0.01) than in LL (+ 3.8%), and power at respiratory compensation point (RCP) increased more (P < 0.05) in HL (+ 9.5%, P < 0.01 and + 11.2%, P < 0.01) than in LL (+ 3.2 and + 3.3%). Cycling mechanical efficiency (8–5%) and economy during specific locomotion (7–7%) increased (P < 0.05) in both groups. This study shows that, for a similar increase in HL had a greater increase in PPO than LL. The efficiency of Hi–Lo is also evidenced 15 days later by higher and power at RCP. This study emphasizes that during the post-altitude period, economy of work greatly increases in both groups.     

The effects of agonist and antagonist muscle activation on the knee extension moment–angle relationship in adults and children

The present study examined the effect of agonist activation and antagonist co-activation on the shape of the knee extension moment–angle relationship in adults and children. Isometric knee extension maximum voluntary contractions (MVCs) were performed at every 5° of knee flexion between 55° and 90° (full extension = 0°) by ten men, ten women, ten boys and ten girls. For each trial, the knee extensors’ voluntary activation level was quantified using magnetic stimulation and the level of antagonist co-activation was quantified from their electromyographical activity. Peak MVC moment was greater for men (264 ± 63 N m) than women (177 ± 60 N m), and greater for adults than children (boys 78 ± 17 N m, girls 91 ± 28 N m) (p < 0.01). The agonistic activation level was greater for adults (~85%) than children (~70%). Similarly, antagonist co-activation was greater for adults than children, but relative to the agonist moment there were no differences between groups (all groups 7–8%). Correcting the peak moment for agonist and antagonist activation levels resulted in moments produced by fully activated agonist muscles of 334 ± 83, 229 ± 70, 114.2 ± 32 and 147 ± 46 N m, for men, women, boys and girls, respectively. Although correcting for shifts in joint angle during contraction altered the angle of peak moment by ~10° (p < 0.01), the peak moment occurred at ~60° for all groups. Changes in tendon stiffness, muscle size and architecture, and the pattern of the moment arm–angle relationship may in combination occur so that as children develop and mature into adults the shape of the moment–angle relationship is not altered.