Intense training: mucosal immunity and incidence of respiratory infections.

This investigation examined the impact of a multistressor situation on salivary immunoglobulin A (sIgA) levels, and incidence of upper respiratory tract infection (URTI) during the French commando training (3 weeks of training followed by a 5-day combat course). For the URTI, the types of symptoms were classified according to the anatomical location of the infection. Saliva samples were collected (8 a.m.) from 21 males [21 (2) years] before entry into the commando training, the morning following the 3 weeks of training, after the 5-day combat course, and after 1 week of recovery. sIgA, protein and cortisol concentrations were measured. Symptoms of URTI were recorded during the study from health logs and medical examinations. After the 3 weeks of training, the sIgA concentration was not changed, although it was reduced after the 5-day course [from 120 (14) mg l(-1) to 71 (9) mg l(-1), P<0.01]. It returned to pre-training levels within a week of recovery. The incidence of URTI increased during the trial (chi(2)=53.48; P<0.01), but was not related to sIgA. Among the 30 episodes of URTI reported, there were 12 rhino-pharyngitis, 6 bronchitis, 5 tonsillitis, 4 sinusitis and 3 otitis. Cortisol levels were raised after the 3-week training (P<0.01), dropping below baseline after the combat course (P<0.01). Stressful situations have an adverse effect on mucosal immunity and incidence of URTI. However, the relationship between sIgA and illness remained unclear. The large proportion of rhino-pharyngitis indicated that the nasopharyngeal cavity is at a higher risk of infection.

Metabolic and vascular support for the role of myoglobin in humans: a multiparametric NMR study.

In human muscle the role of myoglobin (Mb) and its relationship to factors such as muscle perfusion and metabolic capacity are not well understood. We utilized nuclear magnetic resonance (NMR) to simultaneously study the Mb concentration ([Mb]), perfusion, and metabolic characteristics in calf muscles of athletes trained long term for either sprint or endurance running after plantar flexion exercise and cuff ischemia. The acquisitions for (1)H assessment of Mb desaturation and concentration, arterial spin labeling measurement of muscle perfusion, and (31)P spectroscopy to monitor high-energy phosphate metabolites were interleaved in a 4-T magnet. The endurance-trained runners had a significantly elevated [Mb] (0.28 +/- 0.06 vs. 0.20 +/- 0.03 mmol/kg). The time constant of creatine rephosphorylation (tauPCr), an indicator of oxidative capacity, was both shorter in the endurance-trained group (34 +/- 6 vs. 64 +/- 20 s) and negatively correlated with [Mb] across all subjects (r = 0.58). The time to reach maximal perfusion after cuff release was also both shorter in the endurance-trained group (306 +/- 74 vs. 560 +/- 240 s) and negatively correlated with [Mb] (r = 0.56). Finally, Mb reoxygenation rate tended to be higher in the endurance-trained group and was positively correlated with tauPCr (r = 0.75). In summary, these NMR data reveal that [Mb] is increased in human muscle with a high oxidative capacity and a highly responsive vasculature, and the rate at which Mb resaturates is well correlated with the rephosphorylation rate of Cr, each of which support a teleological role for Mb in O(2) transport within highly oxidative human skeletal muscle.

Brief exposure to -2 Gz reduces cerebral blood flow velocity during subsequent +2 Gz acceleration.

In order to determine the implication of the cerebral vasoconstriction occurring under -Gz acceleration in the mechanism of the push-pull effect, four healthy male non-pilots were submitted to a control centrifugation at +2 Gz, and then to an experimental run with identical +2 Gz plateau, but preceded by -2 Gz exposure. Cerebral blood flow velocity (CBFV), pulsatility index, and resistance index (RI) were continually measured with a transcranial Doppler instrument. The decrease in blood pressure and in CBFV was more important during the experimental run, when the change in RI was not different. We concluded that the cerebral vasoconstriction occurring under -2 Gz exposure seems not to be a major contributor in the mechanism of the push-pull effect appearing during subsequent +2 Gz acceleration.

Effect of co-contractions on the cardiovascular response to submaximal static handgrip.

The aim of this study was to investigate the influence of concomitant involuntary contractions of different muscles on heart rate (HR) and blood pressure (BP) during a sustained, submaximal handgrip. Nine male subjects [23.6 (0.4) years, 177.0 (1.5) cm, and 73.0 (2.7) kg, means (SE)] participated in the experiment. The maximal integrated electromyographic activity (IEMG max) of four ipsilateral muscles, flexor digitorum (FD), biceps brachii (BB), rectus abdominalis (RA) and vastus lateralis (VA), was recorded. Then, after 30 min of rest, the subjects maintained a submaximal isometric handgrip for 2 min. Heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure and surface electromyography (EMG) of the four muscles were recorded. The amplitude and power spectrum of the EMG were analysed. During the handgrip the force was kept constant at 43 (1)% of the maximum voluntary contraction (MVC) only for 90 (12) s. After that time, the subjects were unable to maintain the target force which decreased continuously up to the end of the contraction (P<0.01) with a residual force of 27 (3)% MVC at t = 120 s. HR increased from 75 (3) beats x min(-1) at rest to 109 (6) beats x min(-1) at t = 120 s (P<0.01). SBP and DBP also increased from 112 (5) and 81 (2) mm Hg to 176 (5) and 133 (7) mm Hg, respectively (P<0.01). The EMG activity rose significantly for both FD and BB with a moderate increase for RA and VL. In fact, the individual contributions of FD and BB to the EMG activity of the four muscles were 52 (2)% and 37 (2)%, respectively, whereas the RA and VL contributed only 9 (1)% and 1.4 (0.1)%. The amplitude ratio of FD's EMG to the total EMG activity of the four muscles from which recordings were made decreased with time from 72% to 33% (P<0.01). The central command's level of activation, as reflected by the increased EMG activity of the four recorded muscles, was probably high enough to stimulate the cardiovascular centres through cortical spread (sometimes known as cortical irradiation). On the other hand, maintaining an isometric handgrip at 43% MVC reduced local muscle blood flow and metabolites known to stimulate type III and IV afferents then accumulated, which in turn induced a reflex-mediated elevation of blood pressure. However, the relative forces developed by the co-contracting muscles were of low intensity (less than 20% MVC) and short duration compared to those of the muscle group under study. These results suggest that the mass of the muscle groups recruited during a fatiguing submaximal handgrip contributes little to the cardiovascular response.

Recovery of the torque-velocity relationship after short exhausting cycling exercise.

The effects of fatigue upon the torque-velocity (T-omega) relationship in cycling were studied in 11 subjects. Fatigue was induced by short exhausting exercise, on a cycle ergometer, consisting of 4 all-out sprints without recovery. The linear (T-omega) relationship was determined during each all-out sprint, before, during and after the exhausting exercise. The kinetics of the T-omega relationship had permitted the study of the recovery of optimal torque, optimal velocity and their corresponding maximal power outputs (Pmax), 30 s or 1 min after the short exhausting exercise. Fatigue induced a parallel shift to the left of the T-omega relationship which was partly reversed by a parallel shift to the right during recovery. After 30 s recovery optimal velocity, optimal torque and Pmax were slightly lower than the corresponding values before the exhausting exercise; after 1-min optimal velocity and optimal torque had recovered 99% and 97% of their initial values. These mechanical data suggested that the causes of exhaustion were processes that allowed fast recovery of both optimal velocity and optimal torque.

The isometric force that induces maximal surface muscle deoxygenation.

To determine the external force that induces maximal deoxygenation of brachioradialis muscle 32 trained male subjects maintained isometric contractions using the elbow flexor muscles up to the limit time (isotonic part of the isometric contraction, IIC) and beyond that time for 120 s (anisotonic part of the isometric contraction). During IIC each subject maintained relative forces of either 25% and 70% maximal voluntary contraction (MVC), 50% and 100% MVC, or 40% and 60% MVC. Muscle oxygenation was assessed using a near infrared spectroscope, and expressed as a percentage of the reference value (deltaO2rest) which was the difference between the minimal oxygenation obtained after 6 min of ischaemia at rest and the maximal reoxygenation following the release of the tourniquet. During IIC at 25% MVC, muscle oxygenation decreased to 17 (SEM 3)% deltaO2rest, then it levelled off [25 (SEM 1)% deltaO2rest]. After the point at which target force could not be maintained, reoxygenation was very weak. During IIC at 40%, 50%, 60%, and 70% MVC, the lowest muscle oxygenation values were obtained after 15-20 s of contraction and corresponded to -18 (SEM 6), -59 (SEM 12) -31 (SEM 6), and -29 (SEM 6)% deltaO2rest, respectively. For the contraction at 100% MVC, the lowest oxygenation [-19 (SEM 9)% deltaO2rest] was obtained while force was decreasing (69% MVC). During the anisotonic part of the isometric contractions, the greatest reoxygenation rate was obtained after 50% MVC IIC (P < 0.001). Our results showed that during isometric elbow flexions between 25% and 100% MVC, there was no linear relationship between external force and muscle oxygenation, and that the maximal deoxygenation of the brachioradialis muscle was obtained at 50% MVC.

Effects of aerobic exercise on the torque-velocity relationship in cycling.

The kinetics of the torque-velocity (T-omega) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle. A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min (MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate was set at 60 rpm. The T-omega relationship was determined from the velocity data collected during all-out sprints against a 19 N.m braking torque on the same ergometer, according to a method proposed previously. Maximal theoretical velocity (omega zero) and maximal theoretical torque (Tzero) were estimated by extrapolation of the linear T-omega relationship. Maximal power (Pmax) was calculated from the values of Tzero and omega zero (Pmax = 0.25 omega zero Tzero). The T-omega relationships were determined before, immediately after and 5 and 10 min after the aerobic exercise. The kinetics of omega zero, Tzero and Pmax was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in Tzero and 8.8% decrease in Pmax was seen while the decrease in omega zero was nonsignificant, which suggested that Pmax decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in omega zero and 12.8% decrease in Pmax while the decrease in Tzero was nonsignificant, which suggested that the main cause of the decrease in Pmax was probably a slowing of maximal shortening velocity. The short recovery time of the T-omega relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly.

Filling and emptying characteristics of lower limb venous network in athletes. Study by postural plethysmography.

Leg volume changes were assessed in healthy volunteers by mercury strain gauge postural plethysmography in order to study the effects of different types of physical training on lower limb venous distensibility and emptying. Seven endurance trained subjects (E), seven muscle strength trained subjects (M) and seven sedentary subjects (S) were submitted to a tilt table test. The test measured leg filling volumes FV (ml.100 ml-1) during 30 head-up tilt, half-emptying time T1/2 (seconds) and venous output at the 6th second of emptying (VO6) (ml.100 ml-1.min-1) during return to horizontal position. Comparative tests were made using an ANOVA test. Results showed significantly higher values for FV and VO6 in E (FV: 3.9 +/- 0.2 ml.100 ml-1 in E vs 2.5 +/- 0.2 and 2.2 +/- 0.2 ml.100 ml-1 in M and S, respectively; VO6: 9.2 +/- 1.1 ml.100 ml-1.min-1 in E vs 6.9 +/- 0.7 and 5.5 +/- 0.5 ml.100 ml-1.min-1 in M and S, respectively) whereas no significant differences were observed between groups for T1/2. M and S had the same physiological responses to orthostatic stress. Endurance training seems to increase lower limb venous distensibility without affecting venous emptying and venous return from the lower limbs. These results suggest that the greater venous distensibility in endurance-trained subjects does not result from alterations of the visco-elastic properties of deep vein walls and that it is probably a physical response to hypervolemia consecutive to chronic aerobic training.

Influence of posture and training on the endurance time of a low-level isometric contraction.

Classically, the critical force of a muscle (the relative force below which an isometric contraction can be maintained for a very long time without fatigue) is comprised of between 15 and 20% of its maximum voluntary contraction (MVC). However, some authors believe that the value is below 10% MVC. If such is the case, signs that accompany the establishment of muscle fatigue (EMG changes, continuous increase in systolic blood pressure [SBP] and heart rate [HR]) would have to appear more rapidly and with a higher intensity if the muscle is already partially fatigued at the start of maintaining a contraction at 10% MVC. Twelve healthy untrained participants carried out two isometric contractions with the digit flexors: one (test A) began with a maximum contraction sustained for 4 min followed without interruption by a contraction at 10% MVC for 61 min; the other (test B) was a contraction maintained at 10% MVC for 65 min. For test B, after an initial increase of 4 bpm with respect to at rest, HR remained stable until the end of contraction, SBP progressively increased by 24 mm Hg in 28 min, then remained unchanged until the end, and there were no significant changes in EMG (absence of spectral deviation towards low frequencies). For test A, in spite of the initial maximum contraction, changes in the parameters being studied (total maintenance time, HR, SBP, EMG) during maintenance at 10% MVC were identical to those for test B. The results show that (1) when the number and intensity of the co-contractions are minimized by applying an appropriate posture, it is possible to sustain an isometric contraction at 10% MVC for at least 65 min without the appearance of signs of muscle fatigue; (2) the critical force of the digit flexors is higher than 10% MVC.

Physiological effects of downhill skiing at moderate altitude in untrained middle-aged men.

To evaluate whether occasional strong physical activity at moderate altitude for several consecutive days is acceptable in untrained middle-aged people, 10 men (age range, 46-59 years) underwent physical examinations before (control day, D0), during (D1-D8), and after 1 wk of leisure alpine skiing. With respect to D0, the resting concentration of plasma noradrenaline (NOR) increased transiently (p < 0.01) on D2 and then increased to a maximal value from D6-D8 (p < 0.01). There was no significant change in the concentration of adrenaline. Although maximal voluntary contraction of knee extensors diminished on D3 (P < 0.05), that of the digit flexors did not change. Heart rate (HR) and blood pressure at rest in the evening were always higher than control values except on D4 (forced rest). After the stay, there was a reduction in sympathetic activity. This was reflected by a return of NOR to its control value, a decrease in resting HR (64.2 [11.4] beats per minute [bpm]: control: 71.1 [10.1] bpm, P < 0.02), a tendency for triglyceride and insulin resistance to decrease, and a significant increase in alipoprotein A1/alipoprotein A2 (P < 0.01). Our results show that despite signs of fatigue on D3, the effects of physical activity that is relatively intense (HR > 70% maximal HR) together with mild hypoxia are well tolerated by untrained middle-aged men and that the controlled practice of downhill skiing may be accepted into a program to lower cardiovascular risk factors.

Effect of fatigue on maximal velocity and maximal torque during short exhausting cycling.

A group of 24 subjects performed on a cycle ergometer a fatigue test consisting of four successive all-out sprints against the same braking torque. The subjects were not allowed time to recover between sprints and consequently the test duration was shorter than 30 s. The pedal velocity was recorded every 10 ms from a disc fixed to the flywheel with 360 slots passing in front of a photo-electric cell linked to a microcomputer which processed the data. Taking into account the variation of kinetic energy of the ergometer flywheel, it was possible to determine the linear torque velocity relationship from data obtained during the all-out cycling exercise by computing torque and velocity from zero velocity to peak velocity according to a method proposed previously. The maximal theoretical velocity (v(0)) and the maximal theoretical torque (T(0)) were estimated by extrapolation of each torque-velocity relationship. Maximal power (P(max)) was calculated from the values of T(0) and v(0) (P(max) = 0.25v(0)T(0). The kinetics of v(0), T(0) and P(max) was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Fatigue induced a parallel shift to the left of the torque-velocity relationships. The v( 0), T(0) and P(max) decreases were equal to 16.3 percent, 17.3 percent and 31 percent, respectively. The magnitude of the decrease was similar for v(0) and T(0) which suggested that P max decreased because of a slowing of maximal shortening velocity as well as a loss in maximal muscle strength. However, the interpretation of a decrease in cycling v(0) which has the dimension of a maximal cycling frequency is made difficult by the possible interactions between the agonistic and the antagonistic muscles and could also be explained by a slowing of the muscle relaxation rate.

Cardiovascular responses to leisure alpine skiing in habitually sedentary middle-aged men.

In order to evaluate the cardiovascular responses to leisure alpine skiing of habitually sedentary and not particularly active adult men, a series of continuous recordings of heart rate (HR) was performed on 10 subjects aged 51.0 +/- 1.3 years (mean +/- S.E.) during a 6-day ski trip at an altitude of 1000-2485 m. From the very first day, the subjects spontaneously adopted a regimen of intense physical activity, since 17.9% of the HR values recorded on the ski runs were higher than 85% of the maximal theoretical HR [THRmax (beats min-1) = 220--age (years)], which represented 19.5% of the actual skiing time. On day 2, 10.7% of the HR values were higher than 85% THRmax, or 17.9% of actual skiing time. For the entire ski trip, the mean HR during skiing was approximately 126 beats min-1, which corresponds to 75% THRmax. At rest, HR in the morning did not change significantly from days 2 to 6 (from 80 +/- 4 to 75 +/- 4 beats min-1, P > 0.05), whereas HR in the evening correlated significantly with the duration of physical activity during the day (r = 0.487, P < 0.001). In all cases, HR at rest was significantly higher than before the trip, except in the evening of day 4, the day on which the subjects skied less because they were fatigued after skiing in the morning. Systolic blood pressure (SBP) at rest was always lower than the control established before the trip, whether taken in the morning or in the evening.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the heart rate and electromyogram beyond the limit time of an isotonic isometric contraction.

Nine men [24.6 (SEM 1.1) years] carried out isometric contractions (IC) of the right elbow flexors at 50% and 100% of the maximal voluntary contraction (MVC). At 50% MVC they had to maintain IC until the limit time (isotonic IC: IIC50) and beyond for as long as possible (anisotonic IC: AIC50). At 100% MVC, IC was anisotonic since the decrease in force was immediate (AIC100). Measurements of the force, the integrated electromyogram (iEMG) and the heart rate (fc) were made during the entire period of contraction. There was a linear relationship between the iEMG increase and the fc increase for IIC50 and AIC100. This relationship was not found for AIC50. The role played by the peripheral information would seem to have become more important in fc regulation when the isotonic IC preceding the anisotonic IC was sufficiently long (submaximal IIC). It would seem that the idea of muscle exhaustion at the limit time was only relative, and depended greatly on the subject's motivation and his capacity to endure a certain degree of pain.

Complementary roles of central command and muscular reflex in the regulation of heart rate during submaximal isometric contraction.

During submaximal isometric contraction, the heart rate (HR) and the electromyographic activity (EMG) increase continuously. Although activation of the muscle and the cardiovascular center is placed partly under the common control of the central command, the nature of the relationship that may exist between HR and the integrated electromyogram (iEMG) is seldom studied. Seventeen healthy men, 22.4 +/- 0.5 years of age (M +/- SE), performed isometric contractions with the right elbow flexors. Forces of 25, 40, 50 and 65% of the maximum voluntary contraction (MVC) were used, and the contractions were sustained until (isotonic isometric contraction: IIC) and beyond exhaustion (anisotonic isometric contraction: AIC). During IIC, a linear relationship exists between HR and iEMG; the slope of this relationship is independent of the relative force developed, which is in favor of a predominant role played by the central command in HR increase. The increase in the ratio iEMG/HR at the approach of local muscular exhaustion would indicate that at the end of IIC there is an increase in the relative part furnished by the information of peripheral origin in HR regulation. During AIC, the force (F) decreases in an exponential manner and stabilizes at around 25% MVC from tAIC = 70 s on. The iEMG and HR change independently: iEMG decreases like F such that iEMG/F remains constant; HR continues to increase in the first phase corresponding to the rapid decrease in F and iEMG, then in a second phase, it decreases linearly with respect to time. Our results suggest that the action of the central command is dominant during stage 1 of AIC, while during stage 2 the relative part furnished by the muscle reflexes increases. Beyond tAIC = 70 s, there seems to be a certain degree of central fatigue.