High Altitude Increases Alteration in Maximal Torque but Not in Rapid Torque Development in Knee Extensors after Repeated Treadmill Sprinting.

We assessed knee extensor neuromuscular adjustments following repeated treadmill sprints in different normobaric hypoxia conditions, with special reference to rapid muscle torque production capacity. Thirteen team- and racquet-sport athletes undertook 8 × 5-s "all-out" sprints (passive recovery = 25 s) on a non-motorized treadmill in normoxia (NM; FiO2 = 20.9%), at low (LA; FiO2 = 16.8%) and high (HA; FiO2 = 13.3%) normobaric hypoxia (simulated altitudes of ~1800 m and ~3600 m, respectively). Explosive (~1 s; "fast" instruction) and maximal (~5 s; "hard" instruction) voluntary isometric contractions (MVC) of the knee extensors (KE), with concurrent electromyographic (EMG) activity recordings of the vastus lateralis (VL) and rectus femoris (RF) muscles, were performed before and 1-min post-exercise. Rate of torque development (RTD) and EMG (i.e., Root Mean Square or RMS) rise from 0 to 30, -50, -100, and -200 ms were recorded, and were also normalized to maximal torque and EMG values, respectively. Distance covered during the first 5-s sprint was similar (P > 0.05) in all conditions. A larger (P < 0.05) sprint decrement score and a shorter (P < 0.05) cumulated distance covered over the eight sprints occurred in HA (-8 ± 4% and 178 ± 11 m) but not in LA (-7 ± 3% and 181 ± 10 m) compared to NM (-5 ± 2% and 183 ± 9 m). Compared to NM (-9 ± 7%), a larger (P < 0.05) reduction in MVC torque occurred post-exercise in HA (-14 ± 9%) but not in LA (-12 ± 7%), with no difference between NM and LA (P > 0.05). Irrespectively of condition (P > 0.05), peak RTD (-6 ± 11%; P < 0.05), and normalized peak RMS activity for VL (-8 ± 11%; P = 0.07) and RF (-14 ± 11%; P < 0.01) muscles were reduced post-exercise, whereas reductions (P < 0.05) in absolute RTD occurred within the 0-100 (-8 ± 9%) and 0-200 ms (-10 ± 8%) epochs after contraction onset. After normalization to MVC torque, there was no difference in RTD values. Additionally, the EMG rise for VL muscle was similar (P > 0.05), whereas it increased (P < 0.05) for RF muscle during all epochs post-exercise, independently of the conditions. In summary, alteration in repeated-sprint ability and post-exercise MVC decrease were greater at high altitude than in normoxia or at low altitude. However, the post-exercise alterations in RTD were similar between normoxia and low-to-high hypoxia

Can analysis of performance and neuromuscular recoveries from repeated sprints shed more light on its fatigue-causing mechanisms?

International audienc

Editorial: Managing physiological and biomechanical load-adaptation pathways in high performance sport: Challenges and opportunities

High performance sport is continuing to push the barriers of elite athletes' physiological and biomechanical adaptation in an effort to gain an edge in highly competitive sporting environments, where the winning margins can be extremely thin. Methods for individualizing and optimizing the load-adaptation relationship to different training interventions have long been sought (1, 2), and continue to this day (3, 4). But while physiological adaptations to training have been well-studied, differentiating between physiological and biomechanical load-adaptation pathways is vital for understanding how best to optimize individualized training programs (5). Also of significant interest is the use of ergogenic aids such as dietary supplements (6), environmental manipulation (7), or sophisticated footwear designs (8) on physiological and biomechanical training adaptations, respectively. In addition to understanding load-adaptation pathways, and of equal importance, is determining rigorous methodology for assessing training load, so that the load-adaptation relationship can be better quantified (9, 10). However, despite the growing interest in training and ergogenic intervention research, there remains much to be learnt about assessing and managing the load-adaptation pathway within elite athlete populations

Neuro-mechanical determinants of repeated treadmill sprints - Usefulness of an "hypoxic to normoxic recovery" approach.

To improve our understanding of the limiting factors during repeated sprinting, we manipulated hypoxia severity during an initial set and examined the effects on performance and associated neuro-mechanical alterations during a subsequent set performed in normoxia. On separate days, 13 active males performed eight 5-s sprints (recovery = 25 s) on an instrumented treadmill in either normoxia near sea-level (SL; FiO2 = 20.9%), moderate (MH; FiO2 = 16.8%) or severe normobaric hypoxia (SH; FiO2 = 13.3%) followed, 6 min later, by four 5-s sprints (recovery = 25 s) in normoxia. Throughout the first set, along with distance covered [larger sprint decrement score in SH (-8.2%) compared to SL (-5.3%) and MH (-7.2%); P < 0.05], changes in contact time, step frequency and root mean square activity (surface electromyography) of the quadriceps (Rectus femoris muscle) in SH exceeded those in SL and MH (P < 0.05). During first sprint of the subsequent normoxic set, the distance covered (99.6, 96.4, and 98.3% of sprint 1 in SL, MH, and SH, respectively), the main kinetic (mean vertical, horizontal, and resultant forces) and kinematic (contact time and step frequency) variables as well as surface electromyogram of quadriceps and plantar flexor muscles were fully recovered, with no significant difference between conditions. Despite differing hypoxic severity levels during sprints 1-8, performance and neuro-mechanical patterns did not differ during the four sprints of the second set performed in normoxia. In summary, under the circumstances of this study (participant background, exercise-to-rest ratio, hypoxia exposure), sprint mechanical performance and neural alterations were largely influenced by the hypoxia severity in an initial set of repeated sprints. However, hypoxia had no residual effect during a subsequent set performed in normoxia. Hence, the recovery of performance and associated neuro-mechanical alterations was complete after resting for 6 min near sea level, with a similar fatigue pattern across conditions during subsequent repeated sprints in normoxia

Therapeutic Use of Exercising in Hypoxia: Promises and Limitations.

International audienc

Updated analysis of changes in locomotor activities across periods in an international ice hockey game.

The aim of this study was to examine changes in time-motion patterns of elite male ice hockey players during an international game with special reference to the development of fatigue. Ten elite male ice hockey players were filmed during an official international game. Detailed time-motion patterns and behaviours (effective playing, stoppage and resting times, number of shifts, low- and high-intensity skating activities across periods as well as passing, shooting and body checking) were analysed during the three game periods. Shift duration averaged 85.72±4.89 s (44.01±5.71 s of effective playing time and 41.71±4.07 s of stoppage) and was repeated ~7.4±1.8 times per period. Mean effective playing time and effective time per shift decreased over the periods (-6.8±17.3%, P = 0.18, <i>d</i> = 0.71 and -8.5±12.7%, P = 0.20, <i>d</i> = 0.24, respectively), resulting in a shorter distance covered (-12.8±5.7%, P = 0.16, <i>d</i> = 0.46) from period 1 to 3. At similar time intervals, stoppage (+8.2±9.8%, P<0.05, <i>d</i> = 0.78) and bench resting period (+35.6±34.0%, P<0.05, <i>d</i> = 1.26) also increased. The number of sprints performed in period 3 was significantly lower than in period 1 (-46.7±32.1%, P<0.01, <i>d</i> = 1.12). This was accompanied by a lower effective time (-16.8±24.9%, P<0.05, <i>d</i> = 0.82) spent in high-intensity activities (fast forward skating, forward sprinting and fast backward and sprinting) - particularly in forward sprints (-54.8±20.7%, P<0.01, <i>d</i> = 1.07) - in period 3 vs. 1. Detailed analysis of players' time-motion patterns of an international ice hockey game indicates that the capacity to perform intense actions is impeded towards the end of the match (period 3). Assessing performance fatigability may help practitioners to tailor ice hockey-specific training routines to help prevent in-game premature and/or excessive fatigue development

Under the hood: skeletal muscle determinants of endurance performance

LIACS-Managemen

Association of Hematological Variables with Team-Sport Specific Fitness Performance.

PURPOSE: We investigated association of hematological variables with specific fitness performance in elite team-sport players. METHODS: Hemoglobin mass (Hbmass) was measured in 25 elite field hockey players using the optimized (2 min) CO-rebreathing method. Hemoglobin concentration ([Hb]), hematocrit and mean corpuscular hemoglobin concentration (MCHC) were analyzed in venous blood. Fitness performance evaluation included a repeated-sprint ability (RSA) test (8 x 20 m sprints, 20 s of rest) and the Yo-Yo intermittent recovery level 2 (YYIR2). RESULTS: Hbmass was largely correlated (r = 0.62, P<0.01) with YYIR2 total distance covered (YYIR2TD) but not with any RSA-derived parameters (r ranging from -0.06 to -0.32; all P>0.05). [Hb] and MCHC displayed moderate correlations with both YYIR2TD (r = 0.44 and 0.41; both P<0.01) and RSA sprint decrement score (r = -0.41 and -0.44; both P<0.05). YYIR2TD correlated with RSA best and total sprint times (r = -0.46, P<0.05 and -0.60, P<0.01; respectively), but not with RSA sprint decrement score (r = -0.19, P>0.05). CONCLUSION: Hbmass is positively correlated with specific aerobic fitness, but not with RSA, in elite team-sport players. Additionally, the negative relationships between YYIR2 and RSA tests performance imply that different hematological mechanisms may be at play. Overall, these results indicate that these two fitness tests should not be used interchangeably as they reflect different hematological mechanisms

Effects of Repeated-Sprint Training in Hypoxia on Tennis-Specific Performance in Well-Trained Players

This study examined the physiological, physical and technical responses to repeated-sprint training in normobaric hypoxia [RSH, inspired fraction of oxygen (FiO 2 ) 14.5%] vs. normoxia (RSN, FiO 2 20.9%). Within 12 days, eighteen well-trained tennis players (RSH, n=9 vs. RSN, n=9) completed five specific repeated-sprint sessions that consisted of four sets of 5 maximal shuttle-run sprints. Testing sessions included repeated-sprint ability and Test to Exhaustion Specific to Tennis (TEST). TEST's maximal duration to exhaustion and time to attain the 'onset of blood lactate accumulation' at 4 mMol.L (-1) (OBLA) improvements were significantly higher in RSH compared to RSN. Change in time to attain OBLA was concomitant with observations similar in time to the second ventilatory threshold. Significant interaction (P=0.003) was found for ball accuracy with greater increase in RSH (+13.8%, P=0.013) vs. RSN (-4.6%, P=0.15). A correlation (r=0.59, P<0.001) was observed between change in ball accuracy and TEST's time to exhaustion. Greater improvement in some tennis-specific physical and technical parameters was observed after only 5 sessions of RSH vs. RSN in well-trained tennis players