Background Sports nutritional supplements containing branched-chain amino acids (BCAA) have been widely reported to improve psychological and biological aspects connected to central fatigue and performance in endurance exercise, although the topic is still open to debate. The aim of the present study was to determine whether the intake of a commercially available BCAA-based supplement, taken according to the manufacturer’s recommendations, could affect the rating of perceived exertion (RPE) and performance indexes at the beginning (1d) and end of a 9-week (9w) scheduled high intensity interval training program, with an experimental approach integrating the determination of psychometric, performance, metabolic and blood biochemical parameters. Methods This was a randomized double-blind placebo-controlled study. Thirty-two untrained, healthy young adults (20 males and 12 female) were enrolled. A high-intensity endurance cycling (HIEC) test was used to induce fatigue in the participants: HIEC consisted in ten 90 s sprints interspersed by ten 3 min recovery phases and followed by a final step time to exhaustion was used. In parallel with RPE, haematological values (creatine kinase, alanine, BCAA, tryptophan, ammonia and glucose levels), and performance indexes (maximal oxygen consumption - VO 2max , power associated with lactate thresholds - W LT1 , W LT2 and time to exhaustion - TTE) were assessed. All subject took the supplement (13.2 g of carbohydrates; 3.2 g of BCAA and 1.6 g of L-alanine per dose) or placebo before each test and training session. Dietary habits and training load were monitored during the entire training period. Results The administration of the supplement (SU) at 1d reduced RPE by 9% during the recovery phase, as compared to the placebo (PL); at 9w the RPE scores were reduced by 13 and 21% during the sprint and recovery phase, respectively; at 9w, prolonged supplement intake also improved TTE and TRIMP. SU intake invariably promoted a rapid increase (within 1 h) of BCAA serum blood levels and prevented the post-HIEC tryptophan: BCAA ratio increase found in the PL group, at both 1d and 9w. There was no difference in dietary habits between groups and those habits did not change over time; no difference in glycemia was found between SU and PL. VO 2max , W LT1 and W LT2 values improved over time, but were unaffected by supplement intake. Conclusions On the whole, these results suggest that i) the intake of the BCAA-based commercially available supplement used in this study reduces RPE as a likely consequence of an improvement in the serum tryptophan: BCAA ratio; ii) over time, reduced RPE allows subjects to sustain higher workloads, leading to increased TRIMP and TTE.

中文翻译：

---

市售支链氨基酸 - 丙氨酸 - 碳水化合物运动补充剂对高强度耐力自行车测试中感知运动和表现的影响

背景 含有支链氨基酸 (BCAA) 的运动营养补充剂已被广泛报道可改善与中枢疲劳和耐力运动表现相关的心理和生物学方面，尽管该话题仍存在争议。本研究的目的是确定根据制造商的建议摄入市售的基于 BCAA 的补充剂是否会影响感知劳累 (RPE) 的评级和开始 (1d) 和结束时的表现指数一项为期 9 周 (9w) 的预定高强度间歇训练计划，采用实验方法整合心理测量、表现、代谢和血液生化参数的测定。方法 这是一项随机双盲安慰剂对照研究。三十二未经训练，招募了健康的年轻人（20 名男性和 12 名女性）。使用高强度耐力自行车 (HIEC) 测试来诱发参与者的疲劳：HIEC 包括十次 90 秒冲刺，中间穿插十个 3 分钟的恢复阶段，然后使用最后一步时间到精疲力竭。与 RPE 并行的是血液学值（肌酸激酶、丙氨酸、支链氨基酸、色氨酸、氨和葡萄糖水平）和性能指标（最大耗氧量 - VO 2max 、与乳酸阈值相关的功率 - W LT1 、W LT2 和消耗时间 - TTE）进行评估。所有受试者在每次测试和训练之前服用补充剂（13.2 克碳水化合物；每剂 3.2 克 BCAA 和 1.6 克 L-丙氨酸）或安慰剂。在整个训练期间监测饮食习惯和训练负荷。结果 与安慰剂 (PL) 相比，在第 1 天服用补充剂 (SU) 在恢复阶段使 RPE 降低了 9%；在 9w 时，RPE 分数在冲刺和恢复阶段分别降低了 13% 和 21%；在 9w 时，延长补充剂摄入量也改善了 TTE 和 TRMP。在第 1 天和第 9 天，SU 摄入总是促进 BCAA 血清水平的快速增加（在 1 小时内），并防止在 PL 组中发现的 HIEC 后色氨酸：BCAA 比率增加。各组之间的饮食习惯没有差异，而且这些习惯不会随着时间的推移而改变；SU 和 PL 之间没有发现血糖差异。VO 2max 、W LT1 和W LT2 值随着时间的推移而改善，但不受补充剂摄入量的影响。结论 总的来说，这些结果表明 i) 本研究中使用的基于 BCAA 的市售补充剂的摄入降低了 RPE，这可能是由于血清色氨酸：BCAA 比率的改善；ii) 随着时间的推移，降低的 RPE 允许受试者承受更高的工作量，导致增加的 TRIMP 和 TTE。