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

Girard O, Brocherie F, Morin JB, Millet GP - Front Physiol (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Faculty of Biology and Medicine, Institute of Sport Sciences, University of Lausanne Lausanne, Switzerland ; Athlete Health and Performance Research Center, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital Doha, Qatar.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Changes in stride kinematics (A, contact time; B, aerial time; C, step frequency; D, step length). Mean ± SD (n = 13). The repeated-sprint exercise protocol included a first set of eight sprints performed at sea level (SL), moderate (MH) or severe hypoxia (SH), while the second set of four sprints was always performed at SL. C, T, and I, respectively refer to ANOVA main effects of condition, time and interaction between these two factors with P-value and partial eta-squared into brackets. a, b, c, and d significantly different from sprint 1, 4, 8, and 9, respectively (P < 0.05). 1 and 2 significant different from SL and MH, respectively (P < 0.05).
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Figure 3: Changes in stride kinematics (A, contact time; B, aerial time; C, step frequency; D, step length). Mean ± SD (n = 13). The repeated-sprint exercise protocol included a first set of eight sprints performed at sea level (SL), moderate (MH) or severe hypoxia (SH), while the second set of four sprints was always performed at SL. C, T, and I, respectively refer to ANOVA main effects of condition, time and interaction between these two factors with P-value and partial eta-squared into brackets. a, b, c, and d significantly different from sprint 1, 4, 8, and 9, respectively (P < 0.05). 1 and 2 significant different from SL and MH, respectively (P < 0.05).

Mentions: Running kinematics across the repeated sprints are displayed in Figure 3. Whereas step length remained unchanged, both contact and aerial times lengthened and step frequency decreased from sprint 1 to 4. During sprint 4, the increase in contact time and the decrease in step frequency were significantly larger in SH compared to MH (P < 0.05). From sprint 1 to sprint 8, the increase in contact time (+14.5 ± 6.1% vs. +11.2 ± 6.8% and +12.4 ± 5.1%; P < 0.05) and decrease in step frequency (−9.7±4.2% vs. −7.2±3.7% and −8.1±2.7%; P < 0.05) were larger in SH compared to SL and MH. Independently of the condition, aerial time lengthened (+4.2 ± 2.9%; P < 0.05) and step length decreased (−2.5±3.0%; P < 0.05) from sprint 1 to 8. After 6 min of rest between sprints 8 and 9, sprint kinematic values during sprint 9 were not statistically different from those recorded during sprint 1, with also no significant difference between conditions. During subsequent sprints (9–12), irrespectively of the condition, contact time (+10.2 ± 5.2%) and aerial time (+3.8 ± 3.3%) lengthened (P < 0.05), step frequency (−6.2±2.6%) decreased (P < 0.05) and step length (+1.2 ± 3.0%) remained unchanged.


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

Girard O, Brocherie F, Morin JB, Millet GP - Front Physiol (2015)

Changes in stride kinematics (A, contact time; B, aerial time; C, step frequency; D, step length). Mean ± SD (n = 13). The repeated-sprint exercise protocol included a first set of eight sprints performed at sea level (SL), moderate (MH) or severe hypoxia (SH), while the second set of four sprints was always performed at SL. C, T, and I, respectively refer to ANOVA main effects of condition, time and interaction between these two factors with P-value and partial eta-squared into brackets. a, b, c, and d significantly different from sprint 1, 4, 8, and 9, respectively (P < 0.05). 1 and 2 significant different from SL and MH, respectively (P < 0.05).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585155&req=5

Figure 3: Changes in stride kinematics (A, contact time; B, aerial time; C, step frequency; D, step length). Mean ± SD (n = 13). The repeated-sprint exercise protocol included a first set of eight sprints performed at sea level (SL), moderate (MH) or severe hypoxia (SH), while the second set of four sprints was always performed at SL. C, T, and I, respectively refer to ANOVA main effects of condition, time and interaction between these two factors with P-value and partial eta-squared into brackets. a, b, c, and d significantly different from sprint 1, 4, 8, and 9, respectively (P < 0.05). 1 and 2 significant different from SL and MH, respectively (P < 0.05).
Mentions: Running kinematics across the repeated sprints are displayed in Figure 3. Whereas step length remained unchanged, both contact and aerial times lengthened and step frequency decreased from sprint 1 to 4. During sprint 4, the increase in contact time and the decrease in step frequency were significantly larger in SH compared to MH (P < 0.05). From sprint 1 to sprint 8, the increase in contact time (+14.5 ± 6.1% vs. +11.2 ± 6.8% and +12.4 ± 5.1%; P < 0.05) and decrease in step frequency (−9.7±4.2% vs. −7.2±3.7% and −8.1±2.7%; P < 0.05) were larger in SH compared to SL and MH. Independently of the condition, aerial time lengthened (+4.2 ± 2.9%; P < 0.05) and step length decreased (−2.5±3.0%; P < 0.05) from sprint 1 to 8. After 6 min of rest between sprints 8 and 9, sprint kinematic values during sprint 9 were not statistically different from those recorded during sprint 1, with also no significant difference between conditions. During subsequent sprints (9–12), irrespectively of the condition, contact time (+10.2 ± 5.2%) and aerial time (+3.8 ± 3.3%) lengthened (P < 0.05), step frequency (−6.2±2.6%) decreased (P < 0.05) and step length (+1.2 ± 3.0%) remained unchanged.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Faculty of Biology and Medicine, Institute of Sport Sciences, University of Lausanne Lausanne, Switzerland ; Athlete Health and Performance Research Center, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital Doha, Qatar.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus