Meaning of 芯を通す and 芯の通る

Question

In this manga about boxing I found the following unrelated sentences:

1) もっと探れ…　伏黒【ふくろ】さんの拳。小さくても攻撃を未然に防ぐため…　芯を通してくる。

2) 芯の通ったパンチを打ってこなくなって…　後退を優先してる。

In the first the protagonist is thinking about how to anticipate his opponent's punches. In the second he is saying that after he stopped blowing 芯の通ったパンチ his opponent preferred to retreat. What is the exact meaning of 芯を通す and 芯の通る? I think they have something to do with determination and strength, but I am not sure. My attempts:

1) I need to understand Fukuro's punches better. They are not powerful, but to anticipate them I need to focus/be determined.

2) After I stopped blowing strong punches, he preferred to retreat.

Here you can see the two pages where the sentences are taken from. Thank you for your help!

Answer 1

_{(Context: Fukuro (black hair) is a highly defensive boxer who focuses on dodging and feinting rather than trying to knock the opponent out. The protagonist (Riku) is inexperienced and doesn't know how to deal with this type of boxer. Riku wants to induce Fukuro to a vicious exchange of punches, which he is good at, but Fukuro is becoming even more defensive after gaining enough scores to win by decision.)}

Both instances of 芯が通る describe the same thing; Fukuro's not-so-aggressive but clever punches, and his consistently defensive fighting style. Do you remember ～てくる/～てこない refers to something moving toward the speaker? We can tell "I need to focus" and "I stopped blowing punches" are incorrect just by seeing those くる/こない.

芯が通る in this context means something like "to be meaningful/reasonable and consistent", "to have one's own style/belief", etc.

小さくても攻撃を未然に防ぐため…
Although Fukuro's punches are light, they are for preventing my (counter-)attacks.

芯を通してくる。
He is (or his punches are) consistent and reasonable. / He is following his own style.

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芯の通ったパンチを打ってこなくなって…
Fukuro has stopped throwing those (consistently defensive) punches (to me)...

Answer 2

「芯が通る」とは、ここに定義があるように、

物の中心に一本、硬いものが通っているさま。転じて、簡単な困苦には動じない意志や気力が備わっている様子や、考え方が一貫しているさまなどを表す。

また、「芯が通る」をより理解するためには、ここの同音語や類義語を見ると良い。

上記の意味から考えるとOPの１）の解釈は合っているように思う。一方、２）の解釈で示された「強いパンチ」は、結果として強いのであって、気力のこもったパンチ、急所を外さないパンチ、あるいは無駄のない研ぎ澄まされたパンチを意味しており、繰り出したパンチが100％効果的に相手にダメージを与えるから「強い」と解釈すると良いと思う。