肌肉有三種，慢速，快速，超快速。慢速肌肉為“紅色”肌肉，毛細血管豐富，mitochondia多。

超快速肌肉為“白色肌肉”，血液含量少，mitochondria少，一般的cardio運動如長跑鍛煉的是慢速肌肉。隻有高強度鍛煉（HIIT）才能使用超快速肌肉，這樣能刺激生長素（GH）的分泌。這個可能是長壽的解釋之一。

所有跟帖： 

• Do 50 pushups and 5-min plank count as 高強度鍛煉? -7grizzly- ♀ (0 bytes) () 10/01/2014 postreply 09:52:04

• Wow, hats off to you! -60後那一代- ♀ (0 bytes) () 10/01/2014 postreply 12:53:13

• Thanks but those are targets I can only dream of at the moment;- -7grizzly- ♀ (0 bytes) () 10/01/2014 postreply 13:08:22

• They do in my own personal definition :) -Lily168- ♀ (492 bytes) () 10/01/2014 postreply 10:54:24

• Thank you! Sounds like I need to get a grip ;-) -7grizzly- ♀ (0 bytes) () 10/01/2014 postreply 11:44:32