長時間不運動肌肉會變脂肪嗎?

每天都到健身房練身體,時間一久就練出像健美先生般的肌肉

每天都到健身房練身體,時間一久就練出像健美先生般的肌肉

長時間不運動肌肉會變脂肪嗎?

我唸大學時有個同學肌肉練得很壯碩,據他說他每天都到健身房練身體,時間一久就練出像健美先生般的肌肉。最近在同學的群組又看到他,原來的壯碩肌肉不見了,肚子凸不說,連胸肌都變成「男性女乳了」。

可能你身邊也經常看到這樣的例子,所以心中不免有個疑惑:是不是長時間不運動,肌肉都變成脂肪了?

答案是:不會!

肌肉和脂肪細胞型態不同、功能不同

肌肉和脂肪是不同型態的細胞,從中胚層幹細胞分化過來的時候就定型了,肌肉就是肌肉,脂肪就是脂肪。功能不同、外型也不同,不會互相轉換。

健美先生將肌肉練得很壯,他的肌肉細胞數目並沒有增加,只是肌肉細胞的體積增大。此時新陳代謝增加,根據醫學研究,在不做任何運動的情況下,每公斤肌肉每天消耗的熱量大約是13大卡。

舉例來說,一個70公斤、肌肉量50%的男性,肌肉量大約是35公斤,所以一天光是肌肉消耗的熱量就達到455大卡,可以說他多吃一個豬排便當都不會發胖。

肌肉萎縮、脂肪堆積

可是這位先生要是有一天不再練肌肉了,肌纖維就開始縮小。如果他卻照樣吃喝,此時肌肉量可能只剩下原來的一半,這455大卡可能只消耗200大卡,換句話說,每天有255大卡的熱量堆積在體內,你猜產生什麼變化?

當然是油脂越堆越多,包在肌肉外面,再也看不到肌肉的線條了。所以,從外表看起來好像肌肉變成脂肪。

肌肉就是肌肉,脂肪就是脂肪。功能不同、外型也不同,不會互相轉換

參考資料:

Bonus Facts:

  1. There are three main types of muscle cells. The first is smooth muscle, which lines the walls of certain blood vessels and the walls of the esophagus, uterus, stomach, urethra, bladder, and intestines, among other places; this type of muscle is considered involuntary. The second type is cardiac muscle, which is also involuntary and is only found in the heart. The third type is skeletal muscle, which closely resembles cardiac muscle cells and is what most people think of when they think of muscles. Skeletal muscles are attached to tendons which in turn are attached to bones. Cardiac muscle cells tend to be connected in irregular angles, which are called intercalated discs. Skeletal muscle cells, on the other hand, tend to be arranged in parallel bundles.
  2. Within the types of muscle fibers that we can consciously control, there are slow twitch and fast twitch types. Slow twitch muscle cells are much weaker than fast twitch muscle cells, but they are designed for endurance. Fast twitch muscle cells are relatively strong compared to their slow twitch counterparts, but by virtue of their design, have very little staying power.
  3. How muscle cells work is as follows: they contain microscopic filaments with even smaller fibers attached to these filaments. When electricity is carried into the muscle from the outer membrane, the fibers from the filaments hook onto fibers from other filaments and push against each other, thus causing the contraction.
  4. Muscle soreness after workouts, generally appearing the next day, is not caused by lactic acid, as was once thought. Rather, it is caused by tiny tears in the muscle fibers themselves.
  5. Muscles are approximately 18-26% efficient in terms of the total metabolic cost vs. the actual mechanical work done.
  6. On average, 42% of an adult man’s body mass is made up of skeletal muscle. For women, that number drops to 36% on average.
  7. As noted, skeletal muscles consume about 13 Calories per kilogram per day. So, if you weigh approximately 81 kg (180 pounds) and are a man, your skeletal muscles will burn around 442 Calories per day when you are just sit around all day [(81 kg*.42)*13 Calories/kg]. If you are an average female at that same mass, you’ll burn about 379 Calories from your at rest skeletal muscles per day.
  8. Fat cells will burn around 4.5 Calories per kilogram or approximately 1/3 what skeletal muscle cells will burn. How much of your body mass is made up of fat cells varies greatly from person to person, but you can use a body fat test to get that number and then easily figure out how many Calories your fat cells burn per day. ((BodyFatPercentage * weight in kg)*4.5 Calories/kg)
  9. Bone cells burn about 2.3 Calories per kilogram. If you are a man, on average about 15% of your body mass is made up of bone. For women, that number is around 12%.

 
 

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