低氧環境對耐力運動表現及認知功能之影響：探討相關生理機制與營養增補策略

Impacts of hypoxia on performance and cognitive function during endurance exercise: Current understanding of physiological mechanisms and sports nutrition/supplementation strategies

低氧環境使空氣的氧分壓降低，促使體內組織使用氧氣能力下降，中樞及周邊疲勞也較海平面來的更高。雖然，目前已知在高海拔從事耐力運動，會讓身體面對低氧環境，無法發揮正常生理機能而降低運動表現，同時，氧氣壓力減少會導致大腦動脈局部產生組織缺氧，降低認知功能、訊息處理注意力功能以及反應時間增加等，進而影響運動中各種判斷能力上的表現。在眾多高強度耐力運動競技項目，競賽過程需要大腦認知功能去處理臨場反應，判斷各種戰術情境與環境因素等策略，做出對比賽當下最有利的決定，因此每個階段都是勝負的關鍵。例如：鐵人三項運動，其中在自行車項目，利用選手組成集團可以減低風阻效應來達成比賽策略，藉此保留體能進而提升最後一項跑步的表現。然而，在低氧環境進行耐力運動競賽，生理機能會受到更大的挑戰，造成體能上的負擔，而大腦也需要不停判斷、比賽配速、策略及多個運動項目的轉換等問題，且大腦前額葉血流狀態與競賽時所需的認知、思考及判斷有高度相關性，此外前額葉皮層減少氧合作用與降低肌肉力量有關連性，更近一步影響動作控制及判斷能力等問題。目前學界在低氧對腦部血流調控與認知功能之影響仍尚未十分清楚；此外，適當營養增補是否具有改善低氧降低運動表現的正面效益及認知功能，亦是值得進一步深入探討的方向之一。

The hypoxic environment reduces the partial pressure of oxygen, which promotes the stress of oxygen utilization in the tissues of the body. When performing exercise under hypoxic condition, the exercise-induced central and peripheral fatigue is also more obvious than that at sea level. It is well known that endurance exercise at high altitudes induces physiological challenges and thereby reduces endurance sports performance. At the same time, the reduction of oxygen pressure can result in local hypoxia in the cerebral arteries, reduce cognitive function, attention to signal processing, and increase response time, which in turn negatively affect sports performance through impairing decision-making process. In many high-intensity competitive sports events, some races that connect different disciplines (e.g. triathlon) with several transitions process. Athletes need to brain cognitive functions to deal with conditions and face different opponents and a racing course in the game but also need to judge various tactical situations and environmental factors to make the most favorable decisions. Therefore, each transition stage contributes substantially to winning. Reducing wind drag in the bike peloton during cycling racing helps to create a better competitive advantage for the subsequent running performance after the transition, which is the key and last discipline of the race of triathlon. Therefore, the physiological challenges are accumulatively increasing when competing in a high-altitude environment, because racing under low ambient oxygen environment could accelerate the occurrence of fatigue and physical exhaustion. While the status of the cerebral blood flow is highly correlated to the cognition, thinking, and decision making during the pacing, strategies, and transitions in such high-intensity endurance competition events. In addition, the reduction of oxygenation in prefrontal cortex is closely associated with the decrease in muscular contractility, thereby affecting the motor control capacity. However, the effects of hypoxia on the cerebral blood flow and cognitive performance has not been fully clarified yet. Moreover, whether the nutrition ergogenic positively benefits sports and cognitive performance at high-altitude environment still needs to be approved for the further study.