Effects of salbutamol on the contractile properties of human skeletal muscle before and after fatigue.

AIM: The study examined the effects of an oral acute administration of the ß2-agonist salbutamol (Sal) (6 mg) vs. placebo on muscle strength and fatigability in 12 non-asthmatic recreational male athletes in a randomized double-blind protocol. METHODS: Contractile properties of the right quadriceps muscle were measured during electrical stimulations, i.e. twitch, 1-s pulse trains at 20 (P(20) ) and 80 Hz (P(80) ) and during maximal voluntary isometric contraction (MVIC) before (PRE) and after (POST) a fatigue-producing protocol set by an electromyostimulation (30 contractions, frequency: 75 Hz, on-off ratio: 6.25-20s). In addition, the level of muscle voluntary activation was measured. RESULTS: In PRE and POST conditions, the peak torque (PT) of twitch, P(80) and MVIC were not modified by the treatment. The PT in POST P(20) was slightly, although not significantly, less affected by fatigue in Sal compared with placebo condition. Moreover, twitch half-relaxation time at PRE was smaller under Sal than under placebo (P < 0.05). No significant changes in the degree of voluntary activation were observed with Sal treatment in PRE or POST condition. CONCLUSION: Although these findings did not exclude completely an effect of Sal on peripheral factors of human skeletal muscle, oral acute administration of the ß2-agonist Sal seems to be without any relevant ergogenic effect on muscle contractility and fatigability in non-asthmatic recreational male athletes.

Effects of two types of fatigue on the VO(2) slow component.

The aim of the study was to test the hypothesis of the involvement of type II fibres in the V.O (2) slow component phenomenon by using two prior fatiguing protocols on the knee extensor muscles. Nine subjects performed three constant-load cycling exercises at a work rate corresponding to 80 % of their V.O (2) max: (i) preceded by a 20-min fatiguing protocol using electromyostimulation (EMS), (ii) preceded by a 20-min fatiguing protocol using voluntary contractions (VOL), and (iii) without fatiguing protocol (NFP). Voluntary and evoked neuromuscular properties of the knee extensor muscles were tested before (PRE) and after (POST) the two fatiguing protocols. Results show a significant reduction in voluntary force after both fatiguing protocols (-19.9 % and -11.8 %, in EMS and VOL, respectively p<0.01). After EMS, this decrease was greater than after VOL (p<0.05) and was combined with a slackening of muscle contractile properties which was absent after VOL (p<0.05). Regarding the effects on oxygen uptake kinetics, the appearance of the slow component was delayed after EMS and its amplitude was lower than those obtained in VOL and NFP conditions (0.48+/-0.07 vs. 0.75+/-0.09 and 0.69+/-0.08 L . min (-1), respectively; p<0.05). It can thus be concluded that exercises dedicated to preferentially fatiguing type II fibres may alter V.O (2) kinetics.

Effect of inspiratory threshold loading on ventilatory kinetics during constant-load exercise.

Humoral factors play an important role in the control of exercise hyperpnea. The role of neuromechanical ventilatory factors, however, is still being investigated. We tested the hypothesis that the afferents of the thoracopulmonary system, and consequently of the neuromechanical ventilatory loop, have an influence on the kinetics of oxygen consumption (VO2), carbon dioxide output (VCO2), and ventilation (VE) during moderate intensity exercise. We did this by comparing the ventilatory time constants (tau) of exercise with and without an inspiratory load. Fourteen healthy, trained men (age 22.6 +/- 3.2 yr) performed a continuous incremental cycle exercise test to determine maximal oxygen uptake (VO2max = 55.2 +/- 5.8 ml x min(-1) x kg(-1)). On another day, after unloaded warm-up they performed randomized constant-load tests at 40% of their VO2max for 8 min, one with and the other without an inspiratory threshold load of 15 cmH2O. Ventilatory variables were obtained breath by breath. Phase 2 ventilatory kinetics (VO2, VCO2, and VE) could be described in all cases by a monoexponential function. The bootstrap method revealed small coefficients of variation for the model parameters, indicating an accurate determination for all parameters. Paired Student's t-tests showed that the addition of the inspiratory resistance significantly increased the tau during phase 2 of VO2 (43.1 +/- 8.6 vs. 60.9 +/- 14.1 s; P < 0.001), VCO2 (60.3 +/- 17.6 vs. 84.5 +/- 18.1 s; P < 0.001) and VE (59.4 +/- 16.1 vs. 85.9 +/- 17.1 s; P < 0.001). The average rise in tau was 41.3% for VO2, 40.1% for VCO2, and 44.6% for VE. The tau changes indicated that neuromechanical ventilatory factors play a role in the ventilatory response to moderate exercise.

Effects of increased intensity of intermittent training in runners with differing VO2 kinetics.

The purpose of this study was to test the hypothesis that athletes having a slower oxygen uptake ( VO(2)) kinetics would benefit more, in terms of time spent near VO(2max), from an increase in the intensity of an intermittent running training (IT). After determination of VO(2max), vVO(2max) (i.e. the minimal velocity associated with VO(2max) in an incremental test) and the time to exhaustion sustained at vVO(2max) ( T(lim)), seven well-trained triathletes performed in random order two IT sessions. The two IT comprised 30-s work intervals at either 100% (IT(100%)) or 105% (IT(105%)) of vVO(2max) with 30-s recovery intervals at 50% of vVO(2max) between each repeat. The parameters of the VO(2) kinetics (td(1), tau(1), A(1), td(2), tau(2), A(2), i.e. time delay, time constant and amplitude of the primary phase and slow component, respectively) during the T(lim) test were modelled with two exponential functions. The highest VO(2) reached was significantly lower ( P<0.01) in IT(100%) run at 19.8 (0.9) km(.)h(-1) [66.2 (4.6) ml(.)min(-1.)kg(-1)] than in IT(105%) run at 20.8 (1.0) km(.)h(-1) [71.1 (4.9) ml(.)min(-1.)kg(-1)] or in the incremental test [71.2 (4.2) ml(.)min(-1.)kg(-1)]. The time sustained above 90% of VO(2max) in IT(105%) [338 (149) s] was significantly higher ( P<0.05) than in IT(100%) [168 (131) s]. The average T(lim) was 244 (39) s, tau(1) was 15.8 (5.9) s and td(2) was 96 (13) s. tau(1) was correlated with the difference in time spent above 90% of VO(2max) ( r=0.91; P<0.01) between IT(105%) and IT(100%). In conclusion, athletes with a slower VO(2) kinetics in a vVO(2max) constant-velocity test benefited more from the 5% rise of IT work intensity, exercising for longer above 90% of VO(2max) when the IT intensity was increased from 100 to 105% of vVO(2max).

Addition of inspiratory resistance increases the amplitude of the slow component of O2 uptake kinetics.

The contribution of respiratory muscle work to the development of the O(2) consumption (Vo(2)) slow component is a point of controversy because it has been shown that the increased ventilation in hypoxia is not associated with a concomitant increase in Vo(2) slow component. The first purpose of this study was thus to test the hypothesis of a direct relationship between respiratory muscle work and Vo(2) slow component by manipulating inspiratory resistance. Because the conditions for a Vo(2) slow component specific to respiratory muscle can be reached during intense exercise, the second purpose was to determine whether respiratory muscles behave like limb muscles during heavy exercise. Ten trained subjects performed two 8-min constant-load heavy cycling exercises with and without a threshold valve in random order. Vo(2) was measured breath by breath by using a fast gas exchange analyzer, and the Vo(2) response was modeled after removal of the cardiodynamic phase by using two monoexponential functions. As anticipated, when total work was slightly increased with loaded inspiratory resistance, slight increases in base Vo(2), the primary phase amplitude, and peak Vo(2) were noted (14.2%, P < 0.01; 3.5%, P > 0.05; and 8.3%, P < 0.01, respectively). The bootstrap method revealed small coefficients of variation for the model parameter, including the slow-component amplitude and delay (15 and 19%, respectively), indicating an accurate determination for this critical parameter. The amplitude of the Vo(2) slow component displayed a 27% increase from 8.1 +/- 3.6 to 10.3 +/- 3.4 ml. min(-1). kg(-1) (P < 0.01) with the addition of inspiratory resistance. Taken together, this increase and the lack of any differences in minute volume and ventilatory parameters between the two experimental conditions suggest the occurrence of a Vo(2) slow component specific to the respiratory muscles in loaded condition.

Effects of salbutamol and caffeine ingestion on exercise metabolism and performance.

This study was designed to assess the effects of acute oral salbutamol and caffeine intake on performance and metabolism during short-term endurance exercise. Eight healthy volunteers participated in the double-blind placebo-controlled randomized cross-over study. Two 10 min cycling trials were performed at a power corresponding to 90 % VO 2 max for the first and a mock test for the second, separated by 10 min of passive recovery after ingestion of placebo (Pla), salbutamol (Sal, 6 mg) and caffeine (Caf, 250 mg). Performance (mean power during the mock test) was not statistically significant between the 3 treatments. Blood lactate was significantly increased after Sal compared to Pla at rest and until the end of the mock test whereas it appeared significantly increased after Caf compared to Pla at the end of the two exercises. Sal increased basal blood glucose and both Sal and Caf induced significant higher plasma insulin concentrations at rest, at the end of the mock test and during the recovery compared to Pla. No significant changes were found in these three variables between the Sal and the Caf treatments. Plasma growth hormone was significantly decreased after Sal after the mock test compared to the two other treatments. In conclusion, under the conditions of this study, neither oral salbutamol nor caffeine intake produce enhancement of short-term performance in non-specific trained subjects despite the substantial shifts in metabolic and hormonal parameters which were found.

Recovery kinetics of oxygen uptake following severe-intensity exercise in runners.

BACKGROUND: This investigation sought to characterise the oxygen uptake (VO2) off-transient kinetics from severe exercise and to clarify discrepancies between on- and off-transient kinetics for VO2 seen in humans. METHODS: Eleven competitive endurance athletes underwent treadmill running until exhaustion at work-rates corresponding to the speed that elicited approximately 95% of maximal VO2. Gas exchange variables were determined breath-by-breath. Computerised non-linear regression techniques were used to fit the VO2 on- and off-transient kinetics. A 3-exponential model described the VO2 on-transient. VO2 off-transient was analysed to each response time course using 3 different models: a single-exponential model for the entire period and 2 3-exponential models where exponential terms starting either together after a common time delay or after independent time delays. RESULTS: Both 3-exponential models provided an excellent fit (r2>0.90) to the off-transient data. Compared with on-transient, VO2 off-transient kinetics was associated with a slower primary phase (time constant: 16+/-4 vs 39+/-13 sec, p<0.01) but was similar both in time delay and amplitude. CONCLUSIONS: These data indicate that there is no general symmetry between the exercise and recovery kinetics for VO2 because the response of the primary phase of VO2 off-transient resolves to a greater time constant, reflecting altered tissue metabolism. However, the mechanism(s) for the slow component is slow both in developing and to recover within the severe exercise domain.

Decrease in oxygen uptake at the end of a high-intensity submaximal running in humans.

The purpose of the present study was to examine oxygen consumption (VO(2) ) kinetics during severe-intensity running exercise through a four-phase model that considered a decrease in VO(2) at the end of the exercise in light of previous research in which this decrease was only noticed. After determination of maximal oxygen consumption VO(2) max), thirteen highly trained males performed a square-wave running to exhaustion at approximately 95 % of VO(2) max on a level treadmill. VO(2) and ventilatory gas exchange variables were determined breath-by-breath. Computerised non-linear regression techniques incorporating exponential and linear terms were used to describe VO(2) and ventilatory gas exchange variable responses. In contrast with the classical 3-component model that describes the increase in VO(2) for severe-intensity exercise, we observed a 4(th) phase characterised by a significant decrease in VO(2) before exhaustion (slope of VO(2)-time relationship significantly different from a zero value, p < 0.01) in 7 out of 13 subjects. Following a time delay of 31 +/- 44 s after the decrease in VO(2), a significant decrease of minute ventilation (V(E)) was present for 6 of the 7 subjects (p < 0.02). During the exercise for the subjects who decreased V(E), a reduction of 288 +/- 169 ml in tidal volume was associated with an increase of 10.2 +/- 2.4 min(-1) in breathing frequency. These data suggest that the respiratory system might be stressed more for some endurance-trained athletes. The specific link between reduced VO(2) and reduced V(E) remains to be explored.

Is the VO2 slow component dependent on progressive recruitment of fast-twitch fibers in trained runners?

The goal of this study was to use spectral analysis of EMG data to test the hypothesis that the O2 uptake VO2) slow component is due to a recruitment of fast fibers. Thirteen runners carried out a treadmill test with a constant speed, corresponding to 95% of the velocity associated with maximal VO2. The VO2 response was fit with the classical model including three exponential functions. Electrical activity of six lower limb muscles (vastus lateralis, soleus, and gastrocnemius of both sides) was measured using electromyogram surface electrodes. Mean power frequency (MPF) was used to study the kinetics of the electromyogram discharge frequency. Three main results were observed: 1) a common pattern of the MPF kinetics in the six muscles studied was noted; 2) MPF decreased in the first part of the exercise, followed by an increase for all the muscles studied, but only the vastus lateralis, and gastrocnemius muscles of both sides increased significantly (P < 0.05); and 3) the beginning of the MPF increase of the four muscles mentioned above corresponded with the beginning of the slow component. Our results suggest a progression in the average frequency of the motor unit discharge toward the high frequencies, which coheres with the hypothesis of the progressive recruitment of fast-twitch fibers during the VO2 slow component. However, this interpretation must be taken with caution because MPF is the result of a balance between several phenomena.

External loading does not change energy cost and mechanics of rollerski skating.

The purpose of this study was to examine the effects of external loading on the energy cost and mechanics of roller ski skating. A group of 13 highly skilled male cross-country skiers roller skied at 19.0 ( SD 0.1) km x h(-1) without additional load and with loads of 6% and 12% body mass (mb). Oxygen uptake (VO2), knee and ankle joint kinematics, roller-ski electromyogram (EMG) of the vastus lateralis and gastrocnemius lateralis muscles, and roller ski velocity were recorded during the last 40 s of each 4-min period of roller skiing. One-way repeated measures ANOVA revealed that the VO2 expressed relative to total mass (mtot), joint kinetics, eccentric-to-concentric ratio of the integrated EMG, velocity changes within a cycle, and cycle rate did not change significantly with load. The subsequent analysis of the effect of load on each resistance opposing motion suggested that the power to sustain changes in translational kinetic energy, potential energy, and overcoming rolling resistance increased proportionately with the load. The lack of a significant change in VO2/mtot with external loading was associated with a lack of marked change in external mechanical power relative to mtot. The existence of an EMG signal during the eccentric phase prior to the thrust (concentric phase), as well as the lack of significant delay between the two phases, showed that a stretch-shortening cycle (SSC) occurs in roller ski skating. Taken together, the present results would suggest that external loading up to 12% mb does not increase storage and release of elastic energy of lower limb muscles during SSC in roller ski skating.