Biomedical subjects

G Lattier

Publications and source records attributed to G Lattier.

10 recordsLinked to original sources

PubMed2006

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.

Adult↗

PubMed2006

Changes in exercise characteristics, maximal voluntary contraction, and explosive strength during prolonged tennis playing.

OBJECTIVES: To examine changes in exercise characteristics, maximal voluntary contraction, and explosive strength during prolonged tennis playing. METHODS: Maximal isometric voluntary contraction (MVC), leg stiffness (hopping), and peak power in squat (SJ) and countermovement (CMJ) jumps were measured before, every 30 minutes during, and 30 minutes after a three hour tennis match in 12 well trained players. Heart rate (HR), the effective playing time (EPT), rating of perceived exertion (RPE), and muscle soreness of knee extensors were also measured. RESULTS: Decreases in MVC (-9%; p < 0.05) and leg stiffness (-9%; p = 0.17) were observed after the match and were significantly correlated (r = 0.66; p = 0.05). Peak power in SJ and CMJ tests was maintained during the match but was lower (p < 0.001) 30 minutes after. Average HR and EPT were 144 (8) beats/min and 21 (4)% respectively. A strong correlation was found between EPT and HR (r = 0.93; p < 0.05). RPE and muscle soreness increased linearly during the exercise and were significantly correlated (r = 0.99; p < 0.001). CONCLUSIONS: Progressive reductions in maximal voluntary strength and leg stiffness highly correlated with increases in perceived exertion and muscle soreness were observed throughout a three hour tennis match, whereas explosive strength was maintained and decreased only after the match. These alterations may result in less efficient on-court movement and stroke production. They are, however, lower than those reported during continuous exercise of the same duration. The intermittent pattern of tennis and the numerous stretch-shortening cycle movements partly explain these results.

Adult↗

PubMed2005

Why does knee extensor muscles torque decrease after eccentric-type exercise?

AIM: The purpose of this study was to re-examine central and peripheral origins of neuromuscular fatigue after a highly strenuous eccentric exercise of the knee extensor muscles (KE) using both voluntary/evoked contractions and electromyographic recordings (EMG). METHODS: Before, and 30 min after 15 min of intermittent one-logged downhill running, maximal percutaneous electrical stimulations (single twitch, 0.5 s tetanus at 20 Hz and 80 Hz) were applied to the femoral nerve of 10 male subjects. Electrically evoked superimposed twitches were delivered during isometric maximal voluntary contraction (MVC) to determine maximal voluntary activation (%VA). Vastus lateralis (VL), vastus medialis (VM) and biceps femoris (BF) EMG were recorded during MVC and quantified using the root mean square (RMS) value. M-wave characteristics were also determined. RESULTS: KE MVC and %VA decreased significantly with fatigue (-19.6+/-6.1%; P<0.001 and -7.8+/-6.6%; P<0.01, respectively). Peak tetanus tension at 20 and 80 Hz (P20 and P80, respectively) declined (P<0.001), concurrently with a decrement of the P20 x P80(-1) ratio (-37.3+/-16.6%; P<0.001). Antagonist muscle coactivation, RMS to M-wave peak-to-peak amplitude and MVC x P80(-1) ratios were unchanged after the fatiguing exercise. CONCLUSIONS: The results reveal that part of the large loss in MVC may have a central origin but most of the MVC decrement is due to the presence of low-frequency fatigue while possible contractile failure cannot be excluded.

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PubMed2004

Assessment of low-frequency fatigue with two methods of electrical stimulation.

The aim of this study was to compare the use of transcutaneous vs. motor nerve stimulation in the evaluation of low-frequency fatigue. Nine female and eleven male subjects, all physically active, performed a 30-min downhill run on a motorized treadmill. Knee extensor muscle contractile characteristics were measured before, immediately after (Post), and 30 min after the fatiguing exercise (Post30) by using single twitches and 0.5-s tetani at 20 Hz (P20) and 80 Hz (P80). The P20-to-P80 ratio was calculated. Electrical stimulations were randomly applied either maximally to the femoral nerve or via large surface electrodes (ES) at an intensity sufficient to evoke 50% of maximal voluntary contraction (MVC) during a 80-Hz tetanus. Voluntary activation level was also determined during isometric MVC by the twitch-interpolation technique. Knee extensor MVC and voluntary activation level decreased at all points in time postexercise (P < 0.001). P20 and P80 displayed significant time x gender x stimulation method interactions (P < 0.05 and P < 0.001, respectively). Both stimulation methods detected significant torque reductions at Post and Post30. Overall, ES tended to detect a greater impairment at Post in male and a lesser one in female subjects at both Post and Post30. Interestingly, the P20-P80 ratio relative decrease did not differ between the two methods of stimulation. The low-to-high frequency ratio only demonstrated a significant time effect (P < 0.001). It can be concluded that low-frequency fatigue due to eccentric exercise appears to be accurately assessable by ES.

Adult↗

PubMed2004

Fatigue and recovery after high-intensity exercise part I: neuromuscular fatigue.

The contribution of central and peripheral factors to muscle fatigue were quantified following a high-intensity uphill running exercise. Eight male volunteers performed an intermittent exercise at 120 % of maximal aerobic speed on a treadmill with an 18 % grade. Electrically evoked and voluntary contractions of the knee extensors and EMG of the two vastii were analyzed before and immediately after the high-intensity exercise. Isometric maximal voluntary contraction decreased slightly (-7+/-8 %; p < 0.05) after exercise but no changes were found in the level of maximal activation or in the torque produced by a 80 Hz maximal stimulation applied to the femoral nerve. Following exercise, the single twitch was characterized by lower peak torque, maximal rate of force development, and relaxation (-28+/-11%, -25+/-12%, -31+/-15% respectively, p < 0.001), and higher surface of the M-wave for both vastii. The ratio between the torques evoked by 20 Hz and 80 Hz stimulation declined significantly (-22+/-10%, p < 0.01) after exercise. These findings indicate that muscle fatigue after high-intensity running exercise is due to significant alteration in excitation-contraction coupling and that this type of exercise does not induce significant central fatigue or changes at the crossbridge level.

Adult↗

PubMed2004

Fatigue and recovery after high-intensity exercise. Part II: Recovery interventions.

The purpose of this study was to determine the effect of three types of recovery intervention to neuromuscular function after high-intensity uphill running exercise. The 20-min recovery interventions were (i) passive, (ii) active (running at 50 % of maximal aerobic speed), and (iii) low-frequency electromyostimulation. Evoked twitch and maximal voluntary contractions of knee extensor muscles (KE) and EMG of the vastus lateralis and vastus medialis were analysed immediately after the exercise, 10 min after the end of the recovery periods, and 65 min after the exercise (Post65). An all-out running test was also performed 80 min after the end of the fatiguing exercise. No significant differences were noted in any measured parameters but a tendency to a better performance during the all-out test was found after the electromyostimulation intervention (297.5 +/- 152.4 s vs. 253.6 +/- 117.1 s and 260.3 +/- 105.8 s after active and passive recovery, p = 0.13 and p = 0.12, respectively). At Post65, isometric maximal voluntary contraction torque did not return to the pre-exercise values (279.7 +/- 86.5 vs. 298.7 +/- 92.6 Nm, respectively; p < 0.05). During recovery, electrically evoked twitch was characterized by an increase of peak torque, maximal rate of force development and relaxation (+ 24 - 33 %; p < 0.001) but these values were still lower at Post65 than pre-exercise. Amplitude and surface of the M-wave decreased during recovery. These results show that the recovery of the voluntary force-generating capacity of KE after an intermittent high-intensity uphill running exercise do not depend on the type of recovery intervention tested here. It can also be concluded that the recovery of twitch contractile properties does not necessarily follow that of maximal muscle strength.

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PubMed2003

Alteration of neuromuscular function after a prolonged road cycling race.

The aim of this study was to characterize neuromuscular fatigue in knee extensor muscles after a prolonged cycling exercise. During the two days preceding a 140-km race (mean +/- SD duration: 278.2 +/- 24.9 min) and 15 to 30 min after, maximal percutaneous electrical stimulations were applied to the femoral nerve of 11 trained cyclists. Electrically evoked superimposed twitches and trains of 6 stimulations were delivered during isometric maximal voluntary contraction (MVC) to determine maximal voluntary activation (% VA). Knee extensors MVC decreased with fatigue from 158.2 +/- 29.6 to 144.2 +/- 30.0 Nm (p < 0.01), but no central activation failure was detected after the race. The average rate of twitch force development increased significantly from 414 +/- 106 to 466 +/- 102 N x m x s-1 (p < 0.05) and a tendency toward higher peak twitch tension (p = 0.052) was found in the fatigued state. Short tetanus at 20 Hz and 80 Hz were also applied to 4 cyclists, but these fused and unfused tetanic forces were not significantly modified with fatigue. From these results, it can be concluded that the small but significant isometric strength loss measured less than 30 min after the end of a long distance road cycling race is not due to central fatigue. It is also suggested that a raise in peak twitch tension is not necessarily associated with enhanced neuromuscular function.

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PubMed2002

Mechanisms contributing to knee extensor strength loss after prolonged running exercise.

The aim of this study was to identify the mechanisms that contribute to the decline in knee extensor (KE) muscles strength after a prolonged running exercise. During the 2 days preceding a 30-km running race [duration 188.7 +/- 27.0 (SD) min] and immediately after the race, maximal percutaneous electrical stimulations (single twitch, 0.5-s tetanus at 20 and 80 Hz) were applied to the femoral nerve of 12 trained runners. Superimposed twitches were also delivered during isometric maximal voluntary contraction (MVC) to determine the level of voluntary activation (%VA). The vastus lateralis electromyogram was recorded. KE MVC decreased from pre- to postexercise (from 188.1 +/- 25.2 to 142.7 +/- 29.7 N x m; P < 0.001) as did %VA (from 98.8 +/- 1.8 to 91.3 +/- 10.7%; P < 0.05). The changes from pre- to postexercise in these two variables were highly correlated (R = 0.88; P < 0.001). The modifications in the mechanical response after the 80-Hz stimulation and M-wave peak-to-peak amplitude were also significant (P < 0.001 and P < 0.05, respectively). It can be concluded that 1) central fatigue, neuromuscular propagation, and muscular factors are involved in the 23.5 +/- 14.9% reduction in MVC after a prolonged running bout at racing pace and 2) runners with the greatest KE strength loss experience large activation deficit.

Adult↗

PubMed2002

Alterations of neuromuscular function after an ultramarathon.

Neuromuscular fatigue of the knee extensor (KE) and plantar flexor (PF) muscles was characterized after a 65-km ultramarathon race in nine well-trained runners by stimulating the femoral and tibial nerves, respectively. One week before and immediately after the ultramarathon, maximal twitches were elicited from the relaxed KE and PF. Electrically evoked superimposed twitches of the KE were also elicited during maximal voluntary contractions (MVCs) to determine maximal voluntary activation. MVC and maximal voluntary activation decreased significantly after the ultramarathon (-30.2 +/- 18.0% and -27.7 +/- 13.0%, respectively; P < 0.001). Surprisingly, peak twitch increased after the ultramarathon from 15.8 +/- 6.3 to 19.7 +/- 3.3 N. m for PF (P < 0.01) and from 131.9 +/- 21.2 to 157.1 +/- 35.9 N for KE (P < 0.05). Also, shorter contraction and half-relaxation times were observed for both muscles. The compound muscle action potentials (M wave) were not significantly altered by the ultramarathon with the exception of the soleus, which showed a slightly higher M-wave amplitude after the running. From these results, it can be concluded that 65 km of running 1) severely depressed the maximal voluntary force capacity mainly because of a decrease in maximal voluntary activation, 2) potentiated the twitch mechanical response, and 3) did not change significantly the M-wave characteristics.

Adult↗

PubMed2000

Influence of ultra-long-term fatigue on the oxygen cost of two types of locomotion.

The aim of this study was to examine the effects of fatigue induced by a 65-km ultramarathon on the oxygen cost of running (Cr) and cycling (Ccycl). The day before and immediately after the race, a group of nine well-trained male subjects performed two submaximal 4-min exercise bouts: one cycling at a power corresponding to 1.5 W x kg(-1) body mass on an electromagnetically braked ergometer, and one running at 11 km x h(-1) on a flat asphalt roadway. Before oxygen cost determinations, the subjects performed 12 "ankle" jumps at a given frequency that was fixed by an electronic metronome (2.5 Hz). From the non-fatigued to the fatigued condition, there was a significant increase in minute ventilation for both running (P < 0.01) and cycling (P < 0.0001). Significant changes were also found in respiratory exchange ratio both for running (P = 0.01) and cycling (P < 0.0001). However, running and cycling differed in that Cycyc increased significantly by [mean (SD)] 24.2 (11.5)% (P < 0.001), suggesting an alteration of muscle efficiency, while Cr did not change with fatigue [186.8 (14.1) mlO2 x kg(-1) x km(-1) vs 186.8 (18.7) mlO2 x kg(-1) x km(-1)]. In addition, contact times during hopping increased significantly from 0.173 (0.019) ms to 0.194 (0.027) ms (P < 0.01). Analysis of the factors that determine Cr indicate that the subjects modified their movement pattern in order to decrease the mechanical cost of running in such long-term fatigue conditions.

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