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Brocherie F.,University of Lausanne | Millet G.P.,University of Lausanne | Girard O.,University of Lausanne | Girard O.,Athlete Health and Performance Research Center
European Journal of Applied Physiology | Year: 2015

Purpose: This study aimed to determine the neuro-mechanical and metabolic adjustments in the lower limbs induced by the running anaerobic sprint test (the so-called RAST). Methods: Eight professional football players performed 6 × 35 m sprints interspersed with 10 s of active recovery on artificial turf with their football shoes. Sprinting mechanics (plantar pressure insoles), root mean square activity of the vastus lateralis (VL), rectus femoris (RF), and biceps femoris (BF) muscles (surface electromyography, EMG) and VL muscle oxygenation (near-infrared spectroscopy) were monitored continuously. Results: Sprint time, contact time and total stride duration increased from the first to the last repetition (+17.4, +20.0 and +16.6 %; all P < 0.05), while flight time and stride length remained constant. Stride frequency (−13.9 %; P < 0.001) and vertical stiffness decreased (−27.2 %; P < 0.001) across trials. Root mean square EMG activities of RF and BF (−18.7 and −18.1 %; P < 0.01 and 0.001, respectively), but not VL (−1.2 %; P > 0.05), decreased over sprint repetitions and were correlated with the increase in running time (r = −0.82 and −0.90; both P < 0.05). Together with a better maintenance of RF and BF muscles activation levels over sprint repetitions, players with a better repeated-sprint performance (lower cumulated times) also displayed faster muscle de- (during sprints) and re-oxygenation (during recovery) rates (r = −0.74 and −0.84; P < 0.05 and 0.01, respectively). Conclusion: The repeated anaerobic sprint test leads to substantial alterations in stride mechanics and leg-spring behaviour. Our results also strengthen the link between repeated-sprint ability and the change in neuromuscular activation as well as in muscle de- and re-oxygenation rates. © 2014, Springer-Verlag Berlin Heidelberg. Source

Periard J.D.,Athlete Health and Performance Research Center | Racinais S.,Athlete Health and Performance Research Center
Medicine and Science in Sports and Exercise | Year: 2016

Introduction This study examined the influence of alterations in maximal oxygen uptake (VO 2max) in mediating performance and pacing during prolonged self-paced exercise. Methods Twelve well-trained cyclists completed a 750-kJ time trial in temperate (COOL, 18°C), hot (HOT, 35°C), and hypoxic (HYP, 18°C; FiO 2, 0.145) conditions, creating models with a stable, progressively decreasing, and acutely decreased VO 2max, respectively. Results Trial completion was faster in COOL (48.2 ± 5.7 min) compared with HOT (55.4 ± 5.0 min) and HYP (60.1 ± 6.5 min) (P < 0.001), with HOT being faster than HYP (P = 0.028). Core temperature reached 39.0°C ± 0.6°C (COOL), 39.8°C ± 0.5°C (HOT), and 38.5°C ± 0.4°C (HYP; P < 0.01). Power output during COOL was higher than HOT from 40% of work completed onward (P < 0.05) and for the entirety of HYP (P < 0.001), in which it was lower than HOT at 20%-30% (P < 0.05). Normalized power output during COOL and HYP varied by ∼13% and ∼16%, respectively, whereas a ∼27% variation occurred in HOT. VO 2 in COOL was higher than HOT from 70% onward (P < 0.01) and higher than HYP throughout exercise (P < 0.001). Relative to baseline VO 2max (%VO 2max) in normoxia (COOL and HOT) and hypoxia (HYP), %VO 2max during HOT (78% ± 8%) was lower than COOL (84% ± 7%; P = 0.005) and HYP (87% ± 5%; P = 0.003). Conclusions Despite an acutely reduced VO 2max and power output in HYP, pacing and %VO 2max were similar to COOL. In contrast, the progressive decrease in VO 2max and power output in HOT resulted in a more variable pacing pattern with %VO 2max decreasing throughout exercise. These data support the premise that pacing is associated with maintaining an optimal performance intensity, in conjunction with acute and progressive alterations in VO 2max. © 2015 by the American College of Sports Medicine. Source

Periard J.D.,Athlete Health and Performance Research Center | Racinais S.,Athlete Health and Performance Research Center
Journal of Applied Physiology | Year: 2015

This study examined the time course and extent of decrease in peak oxygen uptake (VO2peak) during self-paced exercise in HOT (35°C and 60% relative humidity) and COOL (18°C and 40% relative humidity) laboratory conditions. Ten well-trained cyclists completed four consecutive 16.5-min time trials (15-min self-paced effort with 1.5-min maximal end-spurt to determine VO2peak) interspersed by 5 min of recovery on a cycle ergometer in each condition. Rectal temperature increased significantly more in HOT (39.4 ± 0.7°C) than COOL (38.6 ± 0.3°C; P < 0.001). Power output was lower throughout HOT compared with COOL (P < 0.001). The decrease in power output from trial 1 to 4 was ∼16% greater in HOT (P < 0.001). Oxygen uptake (VO2) was lower throughout HOT than COOL (P < 0.05), except at 5 min and during the end-spurt in trial 1. In HOT, VO2peak reached 97, 89, 85, and 85% of predetermined maximal VO2, whereas in COOL 97, 94, 93, and 92% were attained. Relative exercise intensity (%VO2peak ) during trials 1 and 2 was lower in HOT (∼84%) than COOL (∼86%; P < 0.05), decreasing slightly during trials 3 and 4 (∼80 and ∼85%, respectively; P < 0.05). However, heart rate was higher throughout HOT (P = 0.002), and ratings of perceived exertion greater during trials 3 and 4 in HOT (P < 0.05). Consequently, the regulation of self-paced exercise appears to occur in conjunction with the maintenance of %VO2peak within a narrow range (80-85% VO2peak). This range widens under heat stress, however, when exercise becomes protracted and a disassociation develops between relative exercise intensity, heart rate, and ratings of perceived exertion. Copyright © 2015 the American Physiological Society. Source

Periard J.D.,Athlete Health and Performance Research Center | Racinais S.,Athlete Health and Performance Research Center
Scandinavian Journal of Medicine and Science in Sports | Year: 2015

This study examined the influence of hyperthermia on middle cerebral artery mean blood velocity (MCA Vmean). Eleven cyclists undertook a 750kJ self-paced time trial in HOT (35°C) and COOL (20°C) conditions. Exercise time was longer in HOT (56min) compared with COOL (49min; P<0.001). Power output in HOT was significantly lower from 40% of work completed onward (P<0.01). Rectal temperature increased to 39.6±0.6°C (HOT) and 38.8±0.5°C (COOL; P<0.01). Skin temperature, skin blood flow, and heart rate were higher throughout HOT compared with COOL (P<0.05). A similar increase in ventilation (P<0.05) and decrease in end-tidal partial pressure of CO2 (PETCO2; P<0.05) occurred in both conditions. Arterial blood pressure and oxygen uptake were lower from 50% of work completed onward in HOT compared with COOL (P<0.01). MCA Vmean increased at 10% in both conditions (P<0.01), decreasing thereafter (P<0.01) and to a greater extent in HOT from 40% of work completed onward (P<0.05). Therefore, despite a comparable ventilatory response and PETCO2 in the HOT and COOL conditions, the greater level of thermal strain developing in the heat appears to have exacerbated the reduction in MCA Vmean, in part via increases in peripheral blood flow and a decrease in arterial blood pressure. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Source

Knez W.L.,Athlete Health and Performance Research Center | Periard J.,Athlete Health and Performance Research Center
British Journal of Sports Medicine | Year: 2014

Objectives The purpose of this study was to determine the impact of changes in oxidative stress and antioxidant status in response to playing tennis in HOT (∼36°C and 35% relative humidity (RH)) and COOL (∼22°C and 70% RH) conditions. Methods 10 male tennis players undertook two matches for an effective playing time (ie, ball in play) of 20 min, corresponding to ∼122 and ∼107 min of total play in HOT and COOL conditions, respectively. Core body temperature, body mass and indirect markers of oxidative stress (diacrons reactive oxygen metabolic test) and antioxidant status (biological antioxidant potential test) were assessed immediately prematch, midmatch and postmatch, and 24 and 48 h into recovery. Results Regardless of the condition, oxidative stress remained similar throughout play and into recovery. Likewise, match-play tennis in the COOL had no impact on antioxidant status. However, antioxidants status increased significantly in the HOT compared with COOL environment (p<0.05). Body mass losses (∼0.5 kg) were similar between conditions. Rectal temperature increased during both matches ( p<0.05), but with a greater magnitude in the HOT (39.3±0.5°C) versus COOL (38.7±0.2°C) environment (p<0.05). Conclusions Match-play tennis in the heat does not exacerbate the development of oxidative stress, but significantly increases antioxidant status. These data suggest that the heat stress observed in the HOT environment may provide a necessary signal for the upregulation of antioxidant defence, dampening cellular damage. Source

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