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ABSTRACT: Research into the biomechanical manifestation of fatigue during exhaustive runs is increasingly popular but additional understanding of the adaptation of the spring-mass behaviour during the course of strenuous, self-paced exercises continues to be a challenge in order to develop optimized training and injury prevention programs. This study investigated continuous changes in running mechanics and spring-mass behaviour during a 5-km run. 12 competitive triathletes performed a 5-km running time trial (mean performance: ̴17 min 30 s) on a 200 m indoor track. Vertical and anterior-posterior ground reaction forces were measured every 200 m by a 5-m long force platform system, and used to determine spring-mass model characteristics. After a fast start, running velocity progressively decreased (- 11.6%; P<0.001) in the middle part of the race before an end spurt in the final 400-600 m. Stride length (- 7.4%; P<0.001) and frequency (- 4.1%; P=0.001) decreased over the 25 laps, while contact time (+ 8.9%; P<0.001) and total stride duration (+ 4.1%; P<0.001) progressively lengthened. Peak vertical forces (- 2.0%; P<0.01) and leg compression (- 4.3%; P<0.05), but not centre of mass vertical displacement (+ 3.2%; P>0.05), decreased with time. As a result, vertical stiffness decreased (- 6.0%; P<0.001) during the run, whereas leg stiffness changes were not significant (+ 1.3%; P>0.05). Spring-mass behaviour progressively changes during a 5-km time trial towards deteriorated vertical stiffness, which alters impact and force production characteristics.
International Journal of Sports Medicine 04/2013; · 2.43 Impact Factor
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ABSTRACT: OBJECTIVES: To examine the usefulness of selected physiological and perceptual measures to monitor fitness, fatigue and running performance during a pre-season, 2-week training camp in eighteen professional Australian Rules Football players (21.9±2.0 years). DESIGN: Observational. METHODS: Training load, perceived ratings of wellness (e.g. fatigue, sleep quality) and salivary cortisol were collected daily. Submaximal exercise heart rate (HRex) and a vagal-related heart rate variability index (LnSD1) were also collected at the start of each training session. Yo-Yo Intermittent Recovery level 2 test (Yo-YoIR2, assessed pre-, mid- and post-camp, temperate conditions) and high-speed running distance during standardized drills (HSR, >14.4kmh(-1), 4 times throughout, outdoor) were used as performance measures. RESULTS: There were significant (P<0.001 for all) day-to-day variations in training load (coefficient of variation, CV: 66%), wellness measures (6-18%), HRex (3.3%), LnSD1 (19.0%), but not cortisol (20.0%, P=0.60). While the overall wellness (+0.06, 90% CL (-0.14; 0.02)AUday(-1)) did not change substantially throughout the camp, HRex decreased (-0.51 (-0.58; -0.45)%day(-1)), and cortisol (+0.31 (0.06; 0.57)nmolL(-1)day(-1)), LnSD1 (+0.1 (0.04; 0.06)msday(-1)), Yo-YoIR2 performance (+23.7 (20.8; 26.6)mday(-1), P<0.001), and HSR (+4.1 (1.5; 6.6)mday(-1), P<0.001) increased. Day-to-day ΔHRex (r=0.80, 90% CL (0.75; 0.85)), ΔLnSD1 (0.51 (r=0.40; 0.62)) and all wellness measures (0.28 (-0.39; -0.17)<r<0.25 (0.14; 0.36)) were related to Δtraining load. There was however no clear relationship between Δcortisol and Δtraining load. ΔYo-YoIR2 was correlated with ΔHRex (r=0.88 (0.84; 0.92)), ΔLnSD1 (r=0.78 (0.67; 0.89)), Δwellness (r=0.58 (0.41; 0.75), but not Δcortisol. ΔHSR was correlated with ΔHRex (r=-0.27 (-0.48; -0.06)) and Δwellness (r=0.65 (0.49; 0.81)), but neither with ΔLnSD1 nor Δcortisol. CONCLUSION: Training load, HRex and wellness measures are the best simple measures for monitoring training responses to an intensified training camp; cortisol post-exercise and LnSD1 did not show practical efficacy here.
Journal of science and medicine in sport / Sports Medicine Australia. 01/2013;
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ABSTRACT: This study investigated the effects of Ramadan on activity patterns, body composition and muscle function. 11 moderately active Muslim males were screened 1 month and 1 week before, in the last week of, and 1 month after Ramadan. Activity patterns were assessed during 72 h using a tri-axial accelerometer, body composition was evaluated via bio-electrical impedance and muscle function during maximal isometric contractions with EMG recordings. Data showed a modification of the activity pattern during Ramadan with a higher level of activity from 02:00 to 05:00 h (29±26, 364±323 and 27±22 steps.h - 1 before, during and after Ramadan, respectively, P<0.05). However, total daily energy expenditure was similar during all testing periods (506±156, 542±219 and 545±207 Kcal.day - 1, respectively), partly explaining the lack of influence of Ramadan on body mass (70.9±11, 70.0±9 and 70.8±9 Kg, respectively) and composition (all P>0.05). Maximal force, associated electrical activity and neuromuscular efficiency (torque/EMG ratio) were maintained during Ramadan (torque: 254.6±30 N.m - 1, Neuromuscular efficiency: 1.0±0.4 a.u.) to levels observed before (244.3±26 N.m, 1.1±0.5 a.u.) and after the holy month (252.5±31 N.m, 1.1±0.5 a.u.). In summary, our data suggest that the influence of Ramadan should be considered as a modification in the distribution of activity times during the day.
International Journal of Sports Medicine 04/2012; 33(8):641-6. · 2.43 Impact Factor
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ABSTRACT: The aim of this study was to characterize the effect of a 5 km running time trial on the neuromuscular properties of the plantar flexors. Eleven well-trained triathletes performed a series of neuromuscular tests before and immediately after the run on a 200 m indoor track. Muscle activation (twitch interpolation) and normalized EMG activity were assessed during maximal voluntary contraction (MVC) of plantar flexors. Maximal soleus H-reflexes and M-waves were evoked at rest (i.e. H (MAX) and M (MAX), respectively) and during MVC (i.e. H (SUP) and M (SUP), respectively). MVC significantly declined (-27%; P < 0.001) after the run, due to decrease in muscle activation (-8%; P < 0.05) and M (MAX)-normalized EMG activity (-13%; P < 0.05). Significant reductions in M-wave amplitudes (M (MAX): -13% and M (SUP): -16%; P < 0.05) as well as H (MAX)/M (MAX) (-37%; P < 0.01) and H (SUP)/M (SUP) (-25%; P < 0.05) ratios occurred with fatigue. Following exercise, the single twitch was characterized by lower peak torque (-16%; P < 0.001) as well as shorter contraction (-19%; P < 0.001) and half-relaxation (-24%; P < 0.001) times. In conclusion, the reduction in plantar flexors strength induced by a 5 km running time trial is caused by peripheral adjustments, which are attributable to a failure of the neuromuscular transmission and excitation-contraction coupling. Fatigue also decreased the magnitude of efferent motor outflow from spinal motor neurons to the plantar flexors and part of this suboptimal neural drive is the result of an inhibition of soleus motoneuron pool reflex excitability.
Arbeitsphysiologie 10/2011; 112(6):2323-30. · 2.15 Impact Factor
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ABSTRACT: The aim of the present study was to examine the associations between adaptive responses to an in-season soccer training camp in the heat and changes in submaximal exercising heart rate (HRex, 5-min run at 9 km/h), postexercise HR recovery (HRR) and HR variability (HRV). Fifteen well-trained but non-heat-acclimatized male adult players performed a training week in Qatar (34.6 ± 1.9°C wet bulb globe temperature). HRex, HRR, HRV (i.e. the standard deviation of instantaneous beat-to-beat R-R interval variability measured from Poincaré plots SD1, a vagal-related index), creatine kinase (CK) activity, plasma volume (PV) changes, and post-5-min run rate of perceived exertion (RPE) were collected at six occasions in temperate environmental conditions (22°C). Players also performed the yo-yo intermittent recovery test level 1 (Yo-Yo IR1) in the same environmental conditions (22°C), both at the beginning and at the end of the training week. Throughout the intervention, HRex and HRV showed decreasing (P < 0.001) and increasing (P < 0.001) trends, respectively, while HRR remained unaffected (P = 0.84). Changes in HRex [-0.52, 90% confidence limits (-0.64; -0.38), P < 0.001] and SD1 [0.35 (0.19; 0.49), P < 0.001] were correlated with those in PV. There was no change in RPE (P = 0.92), while CK varied according to training contents (P < 0.001), without association with HR-derived measures. Yo-Yo IR1 performance increased by 7 ± 9% (P = 0.009), which was correlated with changes in HRex [-0.64 (-0.84; -0.28), P = 0.01]. In conclusion, we found that an in-season soccer training camp in the heat can significantly improve PV and soccer-specific physical performance; both of which are associated with changes in HRex during a 5-min submaximal run.
Scandinavian Journal of Medicine and Science in Sports 08/2011; 21(6):e477-85. · 2.87 Impact Factor
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ABSTRACT: To examine the time course of alteration in neural process (spinal loop properties) during prolonged tennis playing, 12 competitive players performed a series of neuromuscular tests every 30 min during a 3-h match protocol. Muscle activation (twitch interpolation) and normalized EMG activity were assessed during maximal voluntary contraction (MVC) of plantar flexors. Spinal reflexes and M-waves were evoked at rest (i.e., H(max) and M(max) , respectively) and during MVC (i.e., H(sup) , V-wave, M(sup) , respectively). MVC torque declined significantly (P<0.001) across the match protocol, due to decrease (P<0.001) in muscle activation and in normalized EMG activity. The impairment in MVC was significantly correlated (r=0.77; P<0.05) with the decline in muscle activation. H(max) /M(max) (P<0.001), H(sup) /M(sup) (P<0.01) and V/M(sup) (P<0.05) ratios were depressed with fatigue and decreased by ∼80%, 46% and 61% at the end of exercise, respectively. Simultaneously, peak twitch torque and M-wave amplitude were significantly (P<0.01) altered with exercise, suggesting peripheral alterations. During prolonged tennis playing, the compromised voluntary strength capacity is linked to a reduced neural input to the working muscles. This central activation deficit partly results from a modulation in spinal loop properties.
Scandinavian Journal of Medicine and Science in Sports 06/2011; 21(3):455-64. · 2.87 Impact Factor
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Archives of Disease in Childhood 10/2010; 95(10):854-5. · 2.88 Impact Factor
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Scandinavian Journal of Medicine and Science in Sports 10/2010; 20 Suppl 3:iv-v. · 2.87 Impact Factor
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S Racinais
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ABSTRACT: Independent of environmental conditions, rectal temperature follows a circadian rhythm with an acrophase in the late afternoon. In neutral environment, this diurnal increase in temperature is believed to have a passive warm-up effect improving muscle contractility, and in turn, muscle force, power and performance. However, a hot environment blunts the diurnal variation in muscle function by only improving muscle contractility, and in turn, muscle force, power and performance in the morning, when body temperature is at its lowest. Despite this diurnal variation in muscle function, long-duration exercise is only slightly affected by the time-of-day in neutral environment. However, higher afternoon body temperatures can reduce the heat storage capacity and result in a reduction in exercise capacity in hot environments. In addition, in parallel to the circadian variations in muscle contractility and central temperature, exercise capacity in hot environment may also be affected by the diurnal variations in melatonin concentration and in the onset of peripheral vasodilatation and sweating.
Scandinavian Journal of Medicine and Science in Sports 10/2010; 20 Suppl 3:80-9. · 2.87 Impact Factor
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J Grantham,
S S Cheung,
P Connes,
M A Febbraio,
N Gaoua,
J González-Alonso,
O Hue,
J M Johnson,
R J Maughan,
R Meeusen,
L Nybo, S Racinais,
S M Shirreffs,
J Dvorak
Scandinavian Journal of Medicine and Science in Sports 10/2010; 20 Suppl 3:161-7. · 2.87 Impact Factor
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ABSTRACT: This review focuses on the effects of different environmental temperatures on the neuromuscular system. During short duration exercise, performance improves from 2% to 5% with a 1 °C increase in muscle temperature. However, if central temperature increases (i.e., hyperthermia), this positive relation ceases and performance becomes impaired. Performance impairments in both cold and hot environment are related to a modification in neural drive due to protective adaptations, central and peripheral failures. This review highlights, to some extent, the different effects of hot and cold environments on the supraspinal, spinal and peripheral components of the neural drive involved in the up- and down-regulation of neuromuscular function and shows that temperature also affects the neural drive transmission to the muscle and the excitation-contraction coupling.
Scandinavian Journal of Medicine and Science in Sports 10/2010; 20 Suppl 3:1-18. · 2.87 Impact Factor
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ABSTRACT: The aim of this study was to investigate whether (1) spinal modulation would change after non-exhausting eccentric exercise of the plantar flexor muscles that produced muscle soreness and (2) central modulation of the motor command would be linked to the development of muscle soreness. Ten healthy subjects volunteered to perform a single bout of backward downhill walking exercise (duration 30 min, velocity 1 ms(-1), negative grade -25%, load 12% of body weight). Neuromuscular test sessions [H-reflex, M-wave, maximal voluntary torque (MVT)] were performed before, immediately after, as well as 1-3 days after the exercise bout. Immediately after exercise there was a -15% decrease in MVT of the plantar flexors partly attributable to an alteration in contractile properties (-23% in electrically evoked mechanical twitch). However, MVT failed to recover before the third day whereas the contractile properties had significantly recovered within the first day. This delayed recovery of MVT was likely related to a decrement in voluntary muscle drive. The decrease in voluntary activation occurred in the absence of any variation in spinal modulation estimated from the H-reflex. Our findings suggest the development of a supraspinal modulation perhaps linked to the presence of muscle soreness.
Arbeitsphysiologie 04/2008; 102(4):439-46. · 2.15 Impact Factor
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ABSTRACT: The main purpose of this study was to investigate the modulations in H-reflex and V-wave responses (spinal loop properties) induced by prolonged locomotion activities. The second purpose was to compare the development of central fatigue between continuous and intermittent running modes. Eleven males randomly performed two 90-min running exercises either continuously (CONT, first ventilatory threshold) or intermittently (INT, 150 s at a velocity 20% higher than that during CONT/30 s of recovery). Neuromuscular tests of the plantar flexors [including M-wave and H-reflex at rest and M-wave and V-wave during maximal voluntary contraction (MVC)] were performed before and 5 and 30 min after the running exercises. During MVC, the torque significantly decreased (P < 0.05) from preexercise to 5 and 30 min postexercise (-11 and -9%, respectively), as did the RMS/M ratio (-11 and -13%, respectively) and the V/M ratio (-19 and -37%, respectively) for the soleus muscle. At rest, the H/M ratio also decreased significantly (P < 0.001) from preexercise to 5 and 30 min postexercise (-61 and -55%, respectively). Last, no difference in the alteration of spinal loop properties was noted between CONT and INT. In conclusion, the results regarding H-reflex and V-wave suggest for the first time a modulation in spinal loop properties after prolonged running.
Journal of Neurophysiology 02/2007; 97(1):596-603. · 3.32 Impact Factor
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ABSTRACT: Sickle cell trait (SCT) is a genetic abnormality affecting the synthesis of normal haemoglobin [Hb] and is the heterozygous form of sickle cell anaemia. The aim of the present study was to compare the ability to repeat maximal cycling sprints (RSA; repeated sprint ability) between SCT carriers (SCT group, n = 7) and a control group with normal haemoglobin [Hb] (n = 7). The two groups performed a 10-s maximal cycling sprint in order to determine the peak power output (P(peak10)). They then performed an RSA test that consisted of five 6-s maximal cycling sprints interspersed with 24 s of passive recovery. For each sprint, the peak power output (P(peak6)) and the work over the 6-s (W6) were calculated. The sum of each W6 developed during the test was considered to be the total work (W(tot)). The decrements over the repeated sprints for P(peak6) (P(6dec)) and W6 (W(6dec)) were also determined. We found no difference in P(peak10), W(tot) and W(6dec) between the two groups. However, the drop in P(peak6) and W6 during the RSA test appeared earlier in the SCT group and the decrease in P(peak6) over the RSA test was greater in the SCT group than in the control group (p < 0.05). In conclusion, we found that: 1) maximal anaerobic performance determined during a single sprint was not altered by SCT, but 2) repeated sprint ability was different in SCT carriers compared with sportsmen with normal Hb.
International Journal of Sports Medicine 12/2006; 27(12):937-42. · 2.43 Impact Factor
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ABSTRACT: This study investigated whether 30 min of acute hot exposure has an additional passive warm-up effect for the improvement in muscle performance in a moderately warm and humid environment. We also sought to determine whether this effect is dependent on the diurnal variation in body temperature. Nine male subjects (age: 31.9 [+/- 5] years, height: 177 [+/- 6] cm, body mass: 69.3 [+/- 10] kg) were tested (CMJ, cycling sprints, and isokinetic contractions of the knee flexors and extensors) in a moderately warm and humid environment (24 [+/- 1] degrees C and 70 [+/- 4] % rh) with and without acute heat exposure (30 min of rest in a sauna at 76 [+/- 2] degrees C and 27 [+/- 1] % rh), both in the morning (07:00 - 09:00 h) and in the evening (17:00 - 19:00 h). Our results indicated a significant effect of both time-of-day and acute heat exposure on leg skin temperature (p < 0.01) but failed to show any effect of time-of-day or acute heat exposure on the various evaluated parameters (CMJ: speed, force, power and height; cycling power: over a half pedal revolution and a total pedal revolution; isokinetic torque: knee extensor and flexor muscles at 4.19 rad x s (-1), 3.14 rad x s (-1), 2.09 rad x s (-1), and 1.05 rad x s (-1)). In conclusion, our data suggest that 30 min of acute hot exposure does not have any passive warm-up effect in a moderately warm and humid environment. Furthermore, the diurnal variation in body temperature has no passive warm-up effect in a moderately warm and humid or in an extremely hot environment.
International Journal of Sports Medicine 01/2006; 27(1):49-54. · 2.43 Impact Factor
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ABSTRACT: The aim of the present study was to investigate the effect of sleep deprivation on shuttle run score (corresponding to an estimated VO2 peak) in middle-aged amateur athletes.
Twenty-two athletes, training 9.2 hours a week (+/-4), performed a Leger and Gadoury shuttle test daily in a 4-day series that included a pre-test in day 0, 28 hours without sleep before test 1 (and 10 another hours after the test and before bedtime for a sleep deprivation of 38 hours), and then 10 hours of sleep before each of days 2 and 3.
Shuttle run score showed no significant difference over the 4 days; however, the change in shuttle run score on day 2 was significantly correlated with the initial score.
This result suggests that effect of sleep deprivation on shuttle run score is dependent on initial score and may encourage high level aerobic athletes to avoid sleep deprivation 2 days before a competition.
The Journal of sports medicine and physical fitness 10/2004; 44(3):246-8. · 0.85 Impact Factor
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ABSTRACT: The aim of this study was to establish the effect of time of day on maximal anaerobic leg power in a tropical environment (French West Indies). Twenty-three physical education students (15 males and 8 females) who trained 10.5 hours a week (SD 6) volunteered to participate in the study. Their mean age, height and body mass were 22.8 (SD 3) years, 172.6 (SD 8) cm, and 64.6 (SD 7) kg, respectively. The chronotype of all subjects was moderate or intermediate. Tests were scheduled at 08 : 00, 13 : 00 and 17 : 00 hours on separate days in random order and constant conditions (room temperature: 28.1 degrees C [SD 0.6], relative room humidity: 62.6 % [SD 3.4]). On test days, the subjects were first measured at rest for body mass, heart rate and rectal temperature and they then performed vertical jump tests and a force-velocity test. The results showed a time-of-day effect on rectal temperature, which was significantly (p < 0.005) higher by the afternoon (13 : 00 and 17 : 00) than the morning (08 : 00). However, our results failed to show any daytime variation in maximal anaerobic power under the influence of tropical climate, which suggests that a hot and humid environment may have blunted the time-of-day effect by a passive warm-up effect.
International Journal of Sports Medicine 05/2004; 25(3):186-90. · 2.43 Impact Factor
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ABSTRACT: This study evaluated the influence of a neutral vs. a moderately warm environment on the diurnal variation in muscular power. Twelve male subjects [27.0 (+/-4) years] performed two different jump tests [a squat jump (SJ) and a counter-movement jump (CMJ)] and a brief maximal sprint on cycle ergometer (CS) in four different conditions (morning/neutral, morning/moderately warm and humid, afternoon/neutral, and afternoon/moderately warm and humid). The morning experiments were conducted between 07:00 and 09:00 h, and the afternoon experiments were conducted between 17:00 and 19:00 h. The mean laboratory temperatures and humidity were 20 (+/-1) degrees C, 70 (+/-5)% and 29 (+/-1) degrees C, 57 (+/-4)% for the neutral and moderately warm and humid conditions, respectively. Rectal temperature and leg skin temperature were significantly dependent on both time-of-day and ambient temperature. An interaction effect (P < 0.05) was noted between time-of-day and ambient temperature for the power developed for the CMJ, the SJ, and half of a pedal revolution during the cycling sprint. In summary, (i) the same subjects were influenced by time-of-day differently, depending on the ambient temperature during testing; (ii) time-of-day affected muscular performance only in the neutral condition, (iii) the moderately warm and humid condition blunted the diurnal variation in muscular performance, and (iv) the effect of the ambient temperature was dependent on time-of-day.
Chronobiology International 05/2004; 21(3):485-95. · 4.03 Impact Factor
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