[書摘] 核心控制與穩定肌群的重要性

總是會聽到有人以腹部的「六塊肌」來判斷一個人核心肌群的強弱,事實是如此嗎?核心控制(Core Control)的關鍵在於肌力(Strength)嗎?腹肌愈有力,運動表現相對的也愈好嗎?在《Anatomy for Runners》中的"動態神經肌肉力量“Dynamic NeuromuscularStrength"這節說的非常的精彩,一塊來看看。

這幾十年來,坊間都會看到核心肌群(Core Muscle)、核心力量(Core Strength)、核心穩定度(Core Stability)等,你也可以在網路上找到數以千記的訓練與器材來改善核心的能力,但在進行之前,先來了解什麼是核心控制(Core Control)。來看看書上的描述:

There are many muscles in the midsection. All muscles do it shorten. When they shorten, one end of the muscle moves towards the other. Some of there muscle like your rectus abdominis(腹直肌)(your six-pack, 六塊肌), your internal and external obliques(腹內外斜肌), and your erector spinae muscles(豎脊肌) cause us to move.

For example, when you contract your six-pack, you either flex your torso foward towards the pelivs, or tuck your pelvis underneath to flatten the lower back. 

In either case, the rectus abdominus contraction produced a distinct movement – a change in position.
(在任何一種情況下,腹直肌的收縮產生了遠端四肢的移動 – 位置的改變。)

一般訓練六塊腹肌指的就是腹直肌的部份。

The problem is that the rectus abdominus and your obliques are more fast twitch, not postural muscles.  By definition, you cannot depend on them to hold your posture in line all day or during a run. They will fatigue and your position and economy will change.

(問題在於腹直肌與腹斜肌更屬於快縮肌,不是用來維持身體姿勢的肌肉群。定義上,你無法依賴這些肌肉群來維持你整天作息的姿勢或是跑步的動作。當他們疲勞時,你的姿勢及效率將會改變。)

關於何謂快縮肌(Fast Twitch)可以參考「肌肉耐力與力量的差別」。

Other muscles in the midsection don’t really have much of an effect on changing position of your upper body or lower body. The transversus abdominus(腹橫肌), the multifidi(多裂肌), and the pelvic floor(骨盆底肌) are more concerned with keeping things in position.  (腹橫肌、多裂肌、骨盆底肌更著重在於固定的工作上。)

The multifidi are thin muscles in the back of your spine. They have the greatest proprioceptive nerves(本體感受神經) of any muscle in the body. They monitor the position of each and every vertebrate in the spine. As you move, they tell your brain exactly how much each vertebrae moved on another vertebrae. Some of this information goes to our brain, and some of it goes in reflexes.

Your transversus has a different job. It runs around the body similarl to the way a corset(馬甲) wraps around the body. If you tighten the corset on a woman’s dress, it prevents movement. When transversus fires, it doesn’t change the position of the body either.

The true definition of core control is how well you can keep your upper body stable on the lower body.
(核心控制的真正定義是如何將上半身保持穩定於下半身。)

關於腹橫肌的部份,可以參考「[書摘] 腰痛,從核心肌群訓練開始」文章的說明囉。過度訓練「移動肌(Movers):腹直肌、腹內外斜肌、豎脊肌」與虛弱無力的「穩定肌(Stabilizers):腹橫肌、多裂肌、骨盆底肌」,在核心控制上會產生重大的問題。

The key feature of core control is not strength, but timing. Research shows that good core control is actually a feed-forward response.
(核心控制的關鍵在於「時間(Timing)」,而不是在於「力量(Strength)」。研究指出,好的核心控制能力其實是一種事先誘發的反應或稱前饋反應。)

If I move my arm out to the side, my brain knows that moving the limb away from my center of mass will change my balance point, and it will naturally kick on my true core stabilizers 40 milliseconds prior to me moving my arm. In the lower body, 110 milliseconds before I move my leg, my brain kicks on to keep my body stable and in line. 

Proper stabilization depends on proactive, not reactive control.
(穩定度取決於前瞻(預應)的控制,而非反應的控制。) 

從下面的圖形中有說明,正常的核心穩定度是與時間有關。大腦知道四肢的移動會改變身體的平衡點,因此動作發生之40~110毫秒,大腦會發送訊號給內部腹部肌群,來維持身體的穩定。

但是若慢生疼痛、姿勢不良(Posture Dysfunction)或是背部疼痛持續超過四週的時間,身體就會喪失前饋肌肉的控制能力。核心肌群雖然被觸發了,但時間點太遲了!

在書上談到一位常跑步的青少女Michelle的例子,做了Single Leg Squat與Single Leg Bridge的動作評估之後,發現是右側髖關節缺乏穩定度,側向與旋轉的髖關節控制能力有問題,進而造成髕股關節綜合症(Patellofemoral Pain Syndrome)。

她開始上網找到了許多的訓練方式,開始進行一連串的「Side-lying leg lifts」、「Single leg squats」、「Elastic band hip abduction」等動作,但五週之後,髕股關節綜合症還是依然存在著。Why?她從評估的結果中得知自己缺乏髖關節的控制能力,並且進行特定的訓練來改善它,但為何沒有改善呢?這問題的答案就在於她「姿勢不良」,她有青少女常見的症狀Female Adolescent Texting Syndrome(F.A.T.S):

F.A.T.S (Female Adolescent Texting Syndrome)

雖然她針對缺乏的肌肉進行獨立的訓練,但肌肉的運作並不是獨自進行的,肌肉群是透過精密的控制交互的進行合作配合,來完成動作。若她無法達到適合的姿勢與核心控制,她的髖關節與骨盆會一直處在不穩定的狀態,控制髖關節的肌肉也是不穩定的。

因此一位物理治療師建議,她需要由內而外來進行改善,先由核心肌群的穩定度開始,讓髖關節肌群有較好的基底在進行運作,並且建立暢行無阻的前饋控制,以確認穩定度發生是在觸地之前。

《Timing is everything.》

書中有談到,除了因為姿勢不良、肌肉不平衡之外,跑者常見的受傷大多數因為穩定肌群缺乏訓練,因此在強化跑步的肌群與速度之前,先著手訓練穩定肌群的控制。

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