硝酸盐补充剂增强了人体骨骼肌的收缩性能。
Nitrate supplementation enhances the contractile properties of human skeletal muscle.
机构信息
School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM.
出版信息
Med Sci Sports Exerc. 2014 Dec;46(12):2234-43. doi: 10.1249/MSS.0000000000000351.
PURPOSE
Dietary nitrate supplementation positively affects cardiovascular function at rest and energy metabolism during exercise in humans and has recently also been reported to markedly enhance the in vitro contractile properties of mouse fast-twitch muscle. The aim of this study was to investigate the effects of short-term nitrate supplementation on the in vivo contractile properties of the skeletal muscle and voluntary muscle function of humans.
METHODS
In a double-blind, randomized, crossover design, 19 healthy untrained men (21 ± 3 yr) ingested a nitrate-rich concentrated beetroot juice (NIT; nitrate dosage, approximately 9.7 mmol·d) and a placebo (PLA) for seven consecutive days. After the last supplementation dose, force was recorded while participants completed a series of voluntary and involuntary (electrically evoked) unilateral isometric contractions of the knee extensors.
RESULTS
NIT enhanced the peak force response to low-frequency electrical stimulation, as follows: maximal twitch (NIT, 149 ± 41 N, vs PLA, 138 ± 37 N; P = 0.008; effect size, r (ES) = 0.56) and submaximal 1- to 20-Hz contractions (5%-10%, ES = 0.53-0.63). Whereas explosive (rising phase) force production during the first 50 ms of evoked maximal twitch and octet contractions (eight electrical impulses at 300 Hz) was also 3%-15% greater after NIT compared with that after PLA (P = 0.023-0.048, ES = 0.52-0.59), explosive voluntary force remained similar (P = 0.510, ES = 0.16). Maximum voluntary force was also unchanged after NIT (P = 0.539, ES = 0.15).
CONCLUSIONS
These results indicate that 7 d of dietary nitrate supplementation enhanced the in vivo contractile properties of the human skeletal muscle. Specifically, nitrate supplementation improved excitation-contraction coupling at low frequencies of stimulation and enhanced evoked explosive force production but did not affect maximum or explosive voluntary force production in untrained individuals.
目的
膳食硝酸盐补充剂可积极影响人体在休息时的心血管功能和运动时的能量代谢，最近还报道称，它可显著增强小鼠快肌的体外收缩性能。本研究旨在调查短期硝酸盐补充对人体骨骼肌的体内收缩性能和随意肌功能的影响。
方法
在一项双盲、随机、交叉设计中，19 名健康未训练的男性（21 ± 3 岁）连续 7 天摄入富含硝酸盐的浓缩甜菜根汁（NIT；硝酸盐剂量约为 9.7 mmol·d）和安慰剂（PLA）。在最后一次补充剂量后，参与者完成一系列单侧等长的自愿和非自愿（电诱发）膝关节伸展肌收缩时，记录力。
结果
NIT 增强了低频电刺激时的峰值力反应，如下所示：最大抽搐（NIT，149 ± 41 N，vs PLA，138 ± 37 N；P = 0.008；效应大小，r（ES）= 0.56）和亚最大 1-20 Hz 收缩（5%-10%，ES = 0.53-0.63）。然而，与 PLA 相比，NIT 后诱发最大抽搐和八分音符收缩（300 Hz 时的八个电脉冲）的前 50 ms 的爆发性（上升阶段）力产生也增加了 3%-15%（P = 0.023-0.048，ES = 0.52-0.59），爆发性自愿力仍然相似（P = 0.510，ES = 0.16）。NIT 后最大自愿力也没有变化（P = 0.539，ES = 0.15）。
结论
这些结果表明，7 天的饮食硝酸盐补充剂增强了人体骨骼肌的体内收缩性能。具体而言，硝酸盐补充剂改善了低频刺激时的兴奋-收缩偶联，并增强了诱发的爆发性力产生，但在未经训练的个体中，不会影响最大或爆发性自愿力产生。
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