Impact of acute hypoxic exposure on neuromuscular and hemodynamic responses during step intensity dynamic constant external resistance leg extension exercise

Objectives

This study examined the effects of acute normoxic and hypoxic exposure on neuromuscular and hemodynamic physiological responses performed during dynamic step muscle actions.

Methods

Thirteen recreationally active men (mean ± SD age: 21.2 ± 2.9 yrs) performed dynamic leg extensions unilaterally under Normoxic (FiO₂ = 21 %) and Hypoxic (FiO₂ = 13 %) conditions in a randomized order at 20 %, 40 %, 60 %, 80 %, and 100 % of their maximal strength. Electromyographic (EMG) amplitude, EMG frequency, (Oxygenated and Deoxygenated hemoglobin; Oxy_Hb, Deoxy_Hb), Total hemoglobin (Total_Hb), and skeletal muscle tissue oxygenation status (StO₂) were measured from the vastus lateralis during all contractions.

Results

There were no detectable differences in the neuromuscular responses between normoxia and hypoxia for EMG amplitude (p = 0.37–0.74) and frequency (p = 0.17–0.83). For EMG amplitude there were general increases with intensity (p < 0.01–0.03). EMG frequency remained similar from 20% to 80% and then increased at 100 % effort (p = 0.02). There was no significant difference in patterns of responses for Oxy_Hb (p = 0.870) and Total_Hb (p = 0.200) between normoxia and hypoxia. StO₂ (p = 0.028) decreased and Deoxy_Hb (p = 0.006) increased under hypoxia compared to normoxia during dynamic step muscle actions performed in a randomized order.

Conclusion

Unlike fatigue, acute hypoxemia in an unfatigued state does not impact the localized neuromuscular responses, but minimally impacts the hemodynamic responses.