Department of Health, Nutrition, and Exercise Sciences, North Dakota State University, PO Box 6050, Department 2620, Fargo, ND 58108, USA.
J Athl Train. 2012 Nov-Dec;47(6):648-54. doi: 10.4085/1062-6050-47.6.05.
Individuals prone to exercise-associated muscle cramps (EAMCs) are instructed to eat bananas because of their high potassium (K(+)) concentration and carbohydrate content and the perception that K(+) imbalances and fatigue contribute to the genesis of EAMCs. No data exist about the effect of bananas on plasma K(+) concentration (K(+)) or plasma glucose concentration (glucose) after exercise in the heat.
To determine whether ingesting 0, 1, or 2 servings of bananas after 60 minutes of moderate to vigorous exercise in the heat alters K(+) or glucose and whether changes in K(+) result from hypotonic fluid effluxes or K(+) ion changes.
Crossover study.
Laboratory.
Nine euhydrated men (age = 27 ± 4 years, height = 180.3 ± 8.4 cm, mass = 84.9 ± 26.1 kg, urine specific gravity ≤ 1.006) without EAMCs volunteered.
INTERVENTION(S): On 3 separate days, participants completed 60 minutes of moderate to vigorous cycling (temperature = 36.4°C ± 1.1°C, relative humidity = 19.4% ± 2.5%) and then ate 0 g (0 servings), 150 g (1 serving), or 300 g (2 servings) of bananas. Blood samples were collected at 3, 5, 15, 30, and 60 minutes postingestion.
MAIN OUTCOME MEASURE(S): The K(+), changes in plasma K(+) content, plasma volume changes, and glucose.
The K(+) differed between conditions at 60 minutes; 2 servings (4.6 ± 0.3 mmol/L [conventional unit = 4.6 ± 0.3 mEq/L]) was greater than 1 serving (4.5 ± 0.2 mmol/L [conventional unit = 4.5 ± 0.2 mEq/L]) and 0 servings (4.4 ± 0.3 mmol/L [conventional unit = 4.4 ± 0.3 mEq/L]) (P < .05). The K(+) was greater at 60 minutes than at 3 and 5 minutes in the 1-serving condition and was greater at 30 and 60 minutes than at 3 and 5 minutes in the 2-servings condition (P < .05). Percentage change in K(+) content was greater only at 30 and 60 minutes postingestion than at baseline in the 2-servings condition (4.4% ± 3.7% and 5.8% ± 2.3% increase, respectively) (P < .05). The plasma volume changes among conditions were unremarkable. The glucose was greater in the 2-servings condition than in all other conditions at 15, 30, and 60 minutes (P < .05).
The effect of banana ingestion on EAMCs is unknown; however, these data suggested bananas are unlikely to relieve EAMCs by increasing extracellular [K(+)] or glucose. The increases in K(+) were marginal and within normal clinical values. The changes in K(+), plasma K(+) content, and glucose do not occur quickly enough to treat acute EAMCs, especially if they develop near the end of competition.
易发生运动相关性肌肉痉挛（EAMC）的个体被建议食用香蕉，因为香蕉钾（K(+))浓度和碳水化合物含量高，并且人们认为 K(+)失衡和疲劳会导致 EAMC 的发生。在热环境中运动后，香蕉对血浆 K(+)浓度 (K(+)) 或血浆葡萄糖浓度 (glucose) 的影响尚无数据。
确定在热环境中剧烈运动 60 分钟后摄入 0、1 或 2 份香蕉是否会改变 K(+) 或 glucose，以及 K(+) 的变化是否是由于低渗性液体流出或 K(+)离子变化引起的。
交叉研究。
实验室。
9 名无 EAMC 的水合状态正常的男性（年龄=27±4 岁，身高=180.3±8.4cm，体重=84.9±26.1kg，尿比重≤1.006）志愿者。
在 3 个不同的日子里，参与者完成了 60 分钟的中等至剧烈的自行车运动（温度=36.4°C±1.1°C，相对湿度=19.4%±2.5%），然后食用 0g（0 份）、150g（1 份）或 300g（2 份）的香蕉。在摄入后 3、5、15、30 和 60 分钟采集血样。
K(+)、血浆 K(+)含量变化、血浆体积变化和 glucose。
60 分钟时各条件之间的 K(+) 存在差异；2 份（4.6±0.3mmol/L [常规单位=4.6±0.3mEq/L]）大于 1 份（4.5±0.2mmol/L [常规单位=4.5±0.2mEq/L]）和 0 份（4.4±0.3mmol/L [常规单位=4.4±0.3mEq/L]）（P<.05）。1 份条件下，60 分钟时的 K(+) 高于 3 分钟和 5 分钟时，而 2 份条件下，30 分钟和 60 分钟时的 K(+) 高于 3 分钟和 5 分钟时（P<.05）。只有在 2 份条件下，摄入后 30 分钟和 60 分钟时的 K(+)含量变化百分比大于基线时（分别增加 4.4%±3.7%和 5.8%±2.3%）（P<.05）。各条件之间的血浆体积变化无明显差异。2 份条件下的 glucose 在 15、30 和 60 分钟时均高于其他所有条件（P<.05）。
香蕉摄入对 EAMC 的影响尚不清楚；然而，这些数据表明，香蕉不太可能通过增加细胞外 [K(+)] 或 glucose 来缓解 EAMC。K(+) 的增加幅度较小，且在正常临床范围内。K(+)、血浆 K(+)含量和 glucose 的变化发生得不够快，无法治疗急性 EAMC，尤其是在比赛接近尾声时发生的情况下。
