Exercise Physiology Laboratory, University of Castilla-La Mancha, Toledo, Spain.
PLoS One. 2012;7(4):e33807. doi: 10.1371/journal.pone.0033807. Epub 2012 Apr 4.
To investigate whether caffeine ingestion counteracts the morning reduction in neuromuscular performance associated with the circadian rhythm pattern.
Twelve highly resistance-trained men underwent a battery of neuromuscular tests under three different conditions; i) morning (10:00 a.m.) with caffeine ingestion (i.e., 3 mg kg(-1); AM(CAFF) trial); ii) morning (10:00 a.m.) with placebo ingestion (AM(PLAC) trial); and iii) afternoon (18:00 p.m.) with placebo ingestion (PM(PLAC) trial). A randomized, double-blind, crossover, placebo controlled experimental design was used, with all subjects serving as their own controls. The neuromuscular test battery consisted in the measurement of bar displacement velocity during free-weight full-squat (SQ) and bench press (BP) exercises against loads that elicit maximum strength (75% 1RM load) and muscle power adaptations (1 m s(-1) load). Isometric maximum voluntary contraction (MVC(LEG)) and isometric electrically evoked strength of the right knee (EVOK(LEG)) were measured to identify caffeine's action mechanisms. Steroid hormone levels (serum testosterone, cortisol and growth hormone) were evaluated at the beginning of each trial (PRE). In addition, plasma norepinephrine (NE) and epinephrine were measured PRE and at the end of each trial following a standardized intense (85% 1RM) 6 repetitions bout of SQ (POST).
In the PM(PLAC) trial, dynamic muscle strength and power output were significantly enhanced compared with AM(PLAC) treatment (3.0%-7.5%; p≤0.05). During AM(CAFF) trial, muscle strength and power output increased above AM(PLAC) levels (4.6%-5.7%; p≤0.05) except for BP velocity with 1 m s(-1) load (p = 0.06). During AM(CAFF), EVOK(LEG) and NE (a surrogate of maximal muscle sympathetic nerve activation) were increased above AM(PLAC) trial (14.6% and 96.8% respectively; p≤0.05).
These results indicate that caffeine ingestion reverses the morning neuromuscular declines in highly resistance-trained men, raising performance to the levels of the afternoon trial. Our electrical stimulation data, along with the NE values, suggest that caffeine increases neuromuscular performance having a direct effect in the muscle.
研究咖啡因摄入是否能对抗与昼夜节律模式相关的晨间神经肌肉性能下降。
12 名高度抗阻训练的男性在三种不同条件下进行了一系列神经肌肉测试：i）上午（10:00）摄入咖啡因（即 3mg/kg；AM(CAFF) 试验）；ii）上午（10:00）摄入安慰剂（AM(PLAC) 试验）；iii）下午（18:00）摄入安慰剂（PM(PLAC) 试验）。采用随机、双盲、交叉、安慰剂对照的实验设计，所有受试者均作为自身对照。神经肌肉测试包括在自由重量深蹲（SQ）和卧推（BP）运动中测量杆位移速度，负荷分别为最大力量（75%1RM 负荷）和肌肉力量适应（1m/s 负荷）。等长最大自主收缩（MVC(LEG)）和右膝等长电诱发力量（EVOK(LEG)）用于确定咖啡因的作用机制。在每次试验开始时（PRE）评估类固醇激素水平（血清睾酮、皮质醇和生长激素）。此外，在每次试验结束时（POST），在 SQ（85%1RM，6 次重复）的标准化剧烈运动后，测量血浆去甲肾上腺素（NE）和肾上腺素。
在 PM(PLAC) 试验中，与 AM(PLAC) 治疗相比，动态肌肉力量和功率输出显著提高（3.0%-7.5%；p≤0.05）。在 AM(CAFF) 试验中，肌肉力量和功率输出高于 AM(PLAC)水平（4.6%-5.7%；p≤0.05），除了用 1m/s 负荷的 BP 速度（p=0.06）。在 AM(CAFF) 期间，EVOK(LEG)和 NE（最大肌肉交感神经激活的替代物）高于 AM(PLAC)试验（分别增加 14.6%和 96.8%；p≤0.05）。
这些结果表明，咖啡因摄入可逆转高度抗阻训练男性晨间神经肌肉下降，使运动表现达到下午试验的水平。我们的电刺激数据以及 NE 值表明，咖啡因通过直接作用于肌肉来提高神经肌肉性能。
