腕を太くしたくて一生懸命腕ばっかりトレーニングをしているけれど、なかなか腕が太くならない人に対して、よく言われるアドバイスがあります。

- スクワットなどの大きな筋肉を鍛えるトレーニングをしないと腕は太くならないよ

私は一概にこれが悪いアドバイスだとは言いませんが、これに何やら科学的っぽい理屈がくっつくことがあります。

スクワットのような種目を行うと
- 成長ホルモンレベルの顕著な増加
- 間接的な発達作用、つまり全身の筋肉への波及効果
が得られ、脚だけでなく腕なども大きくできるんだよ

みたいな。

これが妥当な理屈なのかどうか…トレーニングによってもたらされる内分泌ホルモンに他の筋肉への波及効果があるか調査した研究を2つ紹介します。両者とも同じ研究グループのものです。

この2つの研究では若い健康な男性を以下の2つのグループに分けて比較実験を行っています。

- 低ホルモングループ: 上腕二頭筋のトレのみ
(トレーニング後の内分泌ホルモンレベルはベースから変化なし)
- 高ホルモングループ: 上腕二頭筋のトレ+高ボリュームの脚のトレ
(トレーニング後に成長ホルモン、IGF-1、及びテストステロンが顕著に上昇)

1つ目の研究は筋タンパク質合成とアナボリックシグナルへの急性効果、2つ目の研究は15週間後の筋力と筋肥大を調査したものです。

以下、アブストラクトの太字の部分だけ訳します。

Resistance exercise-induced increases in putative anabolic hormones do not enhance muscle protein synthesis or intracellular signalling in young men
West DW et, al. J Physiol. 2009 Nov 1;587(Pt 21):5239-47. Epub 2009 Sep 7.

http://jp.physoc.org/content/early/2009/09/04/jphysiol.2009.177220.abstract
http://www.ncbi.nlm.nih.gov/pubmed/19736298

Abstract
We aimed to determine whether exercise-induced elevations in systemic concentration of testosterone, growth hormone (GH) and insulin-like growth factor (IGF-1) enhanced post-exercise myofibrillar protein synthesis (MPS) and phosphorylation of signalling proteins important in regulating mRNA translation. Eight young men (20±1.1 y, BMI = 26±3.5 kg・m-2) completed two exercise protocols designed to maintain basal hormone concentrations (LH = low hormone) or elicit increases in endogenous hormones (HH = high hormone). In the LH protocol, participants performed a bout of unilateral resistance exercise with the elbow flexors. The HH protocol consisted of the same elbow flexor exercise with the contra-lateral arm followed immediately by high-volume leg resistance exercise. Participants consumed 25 g of protein after arm exercise to maximize MPS. Muscle biopsies and blood samples were taken as appropriate. There were no changes in serum testosterone, GH or IGF-1 after the LH protocol, whereas there were marked elevations after HH (testosterone, P < 0.001; GH, P < 0.001; IGF-1, P < 0.05). Exercise stimulated a rise MPS in the biceps brachii (rest = 0.040±0.007, LH = 0.071±0.008, HH = 0.064±0.014 %・h-1; P < 0.05) with no effect of elevated hormones (P = 0.72). Phosphorylation of the 70-kDa S6 protein kinase (p70S6K) also increased post-exercise (P < 0.05) with no differences between conditions. We conclude that the transient increases in endogenous purportedly anabolic hormones do not enhance fed-state anabolic signalling or MPS following resistance exercise. Local mechanisms are likely to be of predominant importance for the post-exercise increase in MPS.

本研究では、一時的な内分泌のアナボリック(とされている)ホルモンはレジスタンストレーニング後の摂食状態のアナボリックシグナルおよび筋タンパク質合成を増強しないという結論に至った。筋タンパク質合成の増大は局部のメカニズムが主要な役割を果たしていると考えられる。

Elevations in ostensibly anabolic hormones with resistance exercise enhance neither training-induced muscle hypertrophy nor strength of the elbow flexors.
West DW, et al. J Appl Physiol. 2009 Nov 12.

http://jap.physiology.org/cgi/content/abstract/01147.2009v1
http://www.ncbi.nlm.nih.gov/pubmed/19910330

The aim of our study was to determine whether resistance exercise-induced elevations in endogenous hormones enhance muscle strength and hypertrophy with training. Twelve healthy young men (21.8 +/- 1.2 y, BMI = 23.1 +/- 0.6 kg(.)m(-2)) independently trained their elbow flexors for 15 weeks on separate days and under different hormonal milieu. In one training condition, participants performed isolated arm curl exercise designed to maintain basal hormone concentrations (low hormone, LH); in the other training condition, participants performed identical arm exercise to the LH condition followed immediately by a high volume of leg resistance exercise to elicit a large increase in endogenous hormones (High Hormone, HH). There was no elevation in serum growth hormone (GH), insulin-like growth factor (IGF-1) or testosterone after the LH protocol, but significant (P < 0.001) elevations in these hormones immediately and 15 and 30 min after the HH protocol. The hormone responses elicited by each respective exercise protocol late in the training period were similar to the response elicited early in the training period indicating that a divergent post-exercise hormone response was maintained over the training period. Muscle cross-sectional area increased by 12% in LH and 10% in HH (P < 0.001) with no difference between conditions (condition x training interaction, P = 0.25). Similarly, type I (P < 0.01) and type II (P < 0.001) muscle fiber CSA increased with training with no effect of hormone elevation in the HH condition. Strength increased in both arms but the increase was not different between the LH and HH conditions. We conclude that exposure of loaded muscle to acute exercise-induced elevations in endogenous anabolic hormones enhances neither muscle hypertrophy nor strength with resistance training in young men.

本研究では、若い男性において、負荷を受けた筋肉に対してエクササイズによる急性の内分泌アナボリックホルモンをさらしても、レジスタンストレーニングによる筋肥大および筋力の増進は得られないとの結論に至った。

●まとめ

腕を太くしたかったら、腕のトレーニングをしましょう。