The triceps is the big muscle at the back of your upper arm. Its job is to straighten the elbow, which makes it the partner and opposite of the biceps at the front, which bends the elbow. That pairing is the easiest way to remember it: biceps pulls the arm closed, triceps pushes it open — so push-ups, pushing a heavy door, throwing a ball.

The triceps is the big muscle at the back of your upper arm三頭肌是你上臂後側的一大塊肌肉 Its job is to straighten the elbow它的功能是伸直手肘 which makes it the partner and opposite of the biceps at the front這讓它成為前側二頭肌的搭檔與相反動作 which bends the elbow二頭肌負責的是彎曲手肘 That pairing is the easiest way to remember it這個配對是記住它最簡單的方法 biceps pulls the arm closed, triceps pushes it open二頭肌把手臂拉彎，三頭肌把它推直 so push-ups, pushing a heavy door, throwing a ball所以像伏地挺身、推開重門、丟球都會用到

It matters for two reasons in real life. In the gym, people talk about training triceps because it is actually the larger of the two muscles, so it does more than the biceps to make an arm look big — a fact that surprises students who only ever curl.

It matters for two reasons in real life這在現實生活裡有兩個重要的地方 In the gym, people talk about training triceps在健身房，大家會說要練三頭肌 because it is actually the larger of the two muscles因為它其實是兩塊肌肉裡比較大的那塊 so it does more than the biceps to make an arm look big所以讓手臂看起來壯，三頭肌的功勞比二頭肌大 a fact that surprises students who only ever curl這個事實常常讓只練彎舉的人感到意外

In medicine and biology you meet 'triceps' in careful anatomical names.

In medicine and biology you meet 'triceps' in careful anatomical names在醫學和生物學裡，你會在嚴謹的解剖學名稱裡看到「triceps」

The spelling is the trap: the word ends in -s even when you mean one muscle, so 'a triceps' is correct, and the plural is 'triceps' too (a few writers use 'tricepses', but it looks odd). Gym speakers everywhere shorten it to 'tris' — chest and tris today.

The spelling is the trap拼法就是陷阱所在 the word ends in -s even when you mean one muscle即使指的是一塊肌肉，這個字結尾還是有-s so 'a triceps' is correct所以「a triceps」是對的 and the plural is 'triceps' too複數也一樣是「triceps」 (a few writers use 'tricepses', but it looks odd)(有少數人會寫「tricepses」，但看起來很怪) Gym speakers everywhere shorten it to 'tris'健身房裡到處都把它簡稱為「tris」 chest and tris today像「今天練胸和三頭(chest and tris)」