The fatigue-induced alteration in postural control is larger in hypobaric than in normobaric hypoxia.

To test the hypothesis that postural control would be more affected by plantar flexors fatigue during acute exposure in hypobaric (HH) than in normobaric (NH) hypoxia or normobaric normoxia (NN). Twelve young male adults performed in a random order three experimental sessions (in HH and NH (FiO2 0.139) at an altitude of 2950 m, and in NN at 500 m) composed of a bipedal postural control with eyes open on a posturographic platform before and after a plantar flexors fatiguing protocol. Center of pressure (CoP) trajectory and stabilogramm diffusion analyses (SDA) parameters were assessed. A two-way repeated measures analysis of variance was used to identify differences by examination of the group and time interaction. Surface of CoP trajectory analysis, increased at POST in HH (p < 0.001) and in NH (p < 0.01) compared to NN. SDA confirmed that PC was more altered in HH than in NH (p < 0.001) and NN (p < 0.05) at POST. The plantar flexor fatigue-induced alteration in postural control increased to a larger extent in HH than in NH or NN, suggesting an alleviating influence of the decreased barometric pressure per se and a mechanical influence of the higher breathing frequency in HH.

Participating In The Race Across AMerica In A Team Of Eight Cyclists: Do Not Neglect Crew Preparation.

BACKGROUND: The Race Across AMerica (RAAM) is considered as one of the longest, and most difficult cycling races in the world. It can be performed in solo or in relay of two, four or eight persons. PURPOSE/METHOD: The aim of the present study was to investigate several physiological, perceptual and psychological responses before, during and after RAAM in a team of eight amateur cyclists. Because logistics of all team is demanding and complex, crew members have followed the same testing procedure. RESULTS: The main result is that parameters were globally not altered to a greater extent in cyclists than in crew members over the course of the RAAM, and that all variables returned to pre-race levels 1 week after the end of the race in both groups. In crew, body fat was decreased (p < 0.05) at mid-race (Mid) vs 1 week before the RAAM (Pre) (-1.5%) and total body water was increased (p < 0.05) at Mid vs Pre (+2.5%). In pre-relay quadriceps strength in cyclists was significantly lower (p < 0.05) at Mid vs Pre (41.6 ± 9.1 vs 45.0 ± 11.2 N, d = 0.36). Therefore, performing the race with eight well-prepared amateur cyclists seems to decrease potential risks on health. In crew, quadriceps strength remained stable at each assessment time but general fatigue increased all along the race. Anger was increased (p < 0.05) at Mid vs Pre in crew. CONCLUSION: The most important message of this study is that crew members for a team of eight require adequate and sufficient preparation and training. Roles and responsibilities need to be thoroughly defined; individuals need to know each other beforehand and they must be prepared for sleep deprivation. The results of this study show the importance of the preparation of two teams: crew members, as well as cyclists.

Postural Control Follows a Bi-Phasic Alteration Pattern During Mountain Ultra-Marathon.

It is well knows that postural control (PC) is deteriorated with neuromuscular fatigue, altitude or sleep deprivation induced by a mountain ultra-marathon (MUM). Several regulatory mechanisms have also been reported during this type of event and the changes in PC at different points of MUM remain unknown. The purpose of this study was to investigate the time course of PC during an extreme MUM. We tested the hypothesis that PC alteration would not increase linearly. Methods: 16 participants (age 45.1 ± 9.6 years) were tested bipedaly on a posturographic platform for 51.2 s with eyes open every ∼50 km. Both traditional and stabilogram diffusion analyses (SDA) were performed. A visual analog scale (VAS) was used for a subjective evaluation of global fatigue, sleep feeling and pain. Results: The main parameters (center of pressure trajectory analysis) increased significantly (p < 0.001, d = 1.56, very large) until km 100. This was confirmed by SDA in the antero-posterior plane. Short term effective diffusion coefficient significantly increased (p < 0.001, d = 1.07, very large) as critical point (p < 0.01, d = 1.57, very large). From km 100 to 200, a different response was observed with a continuous decrease in most of the PC parameters. This was confirmed by SDA in the antero-posterior plane. Short term effective diffusion coefficient significantly increased (p < 0.001, d = 1.39, very large) as critical point (p < 0.01, d = 1.51, very large). Conclusion: Posture alteration is progressively increased until 100 km. After this point, compensatory mechanisms appear to limit the posture degradation. This bi-phasic response is of interest for better understanding the coping with extreme fatigue.