Many of you will have eaten turkey over the Thanksgiving holidays.\u00a0 Some people prefer white meat while others prefer dark meat.\u00a0 What is the difference?<\/p>\n
Dark meat is composed of red muscle fibers (cells).\u00a0 The red color comes from a high concentration of myoglobin in the fibers.\u00a0 Myoglobin, like the hemoglobin in our red blood cells, binds oxygen that can be released as needed to the muscle fibers to allow them to contract.\u00a0 The myoglobin increases the entry of oxygen to the muscle fibers.\u00a0 Contraction of muscles allows for such useful activities as walking, flying and capturing food. Red muscle also has an abundance of capillaries to help provide oxygen to the fibers.<\/p>\n
Red muscle fibers are quite narrow and so have a very high surface area relative to their volume.\u00a0 As a result, oxygen does not have to move very far as it diffuses into the muscle cells.\u00a0 The flight muscles of small songbirds (and small bats) have the highest aerobic capacity of any vertebrate species.<\/p>\n
Red muscle fibers are often referred to as slow twitch fibers.\u00a0 The fibers contract but at a relatively slow rate.\u00a0 The fibers require lots of oxygen to do their work but his oxygen is provided by the blood and stored in the myoglobin until needed by the muscles.\u00a0 As a result, red muscles can do slow but steady work; they do not tend to fatigue.\u00a0 Red muscles are excellent for sustained flight.<\/p>\n
The breast of a turkey, on the other hand, is made up of white muscle fibers.\u00a0 These muscles are not well supplied with capillaries and do not contain much myoglobin to help store oxygen.\u00a0 White fibers are often referred to as fast twitch muscles. They are capable of very rapid contraction.\u00a0 However, these contractions occur in the absence of oxygen.\u00a0\u00a0 After a short period of time, a waste product called lactic acid accumulates in the cells, causing the fast twitch muscle fibers to cease contracting.\u00a0 White fibers are therefore capable of a few very powerful, very strong contractions but tire quickly.<\/p>\n
Let\u2019s return to our turkey.\u00a0 The muscles of the thigh and drumsticks are composed of red muscle fibers.\u00a0 These muscles are used for walking and scratching the ground.\u00a0 The muscles do not have to act particularly quickly.\u00a0 Because they are slow twitch muscles, they do not tend to fatigue.\u00a0 A turkey can walk around all day without experiencing muscle fatigue.<\/p>\n
The flight muscles of the turkey (the breast muscles) are white, fast twitch fibers.\u00a0 When alarmed, a turkey can use those fast twitch fibers to take off explosively.\u00a0 However, the flight must be a short one because those white fibers quickly fatigue as lactic acid builds up in the muscles.<\/p>\n
In most birds, muscles are not made up of only white fibers or only red fibers.\u00a0 In turkey breast muscles, there are some red fibers among the many white fibers.\u00a0 Similarly, the red breast muscles of a pigeon have a few white fibers scattered throughout.\u00a0 Exceptions to the rule occur in the breast muscles of sparrows and hummingbirds that only have red fibers.<\/p>\n
The relative quantity of slow versus fast twitch muscles is related to the particular life style of a bird.\u00a0 For long distance migrants like tanagers, sandpipers or warblers, their flight muscles must be able to sustain long periods of use.\u00a0 White fibers would be poorly suited to the task so it comes as no surprise that the breast or flight muscles of these birds are mostly red muscle.<\/p>\n
On the other hand, the great power but short duration of white fiber contractions makes white breast muscles suitable for birds that need to take evasive action in flight to avoid predators or to fly through thickly forested habitats.<\/p>\n
The size of the breast muscles in a bird is related to its flying ability.\u00a0 In birds that are powerful fliers, over 20% of the bird\u2019s weight is breast muscle.\u00a0 In birds that do not fly, less than 10% of the body weight comes from the breast muscles.\u00a0 The very large breast muscles of domestic turkeys would indicate they are powerful fliers.\u00a0 However, the size of the domestic turkey\u2019s breast muscles is a result of selective breeding.<\/p>\n
The breast muscles of a bird belong to the group of muscles called voluntary or skeletal muscles.\u00a0 A bird can consciously cause those muscles to contract to allow movement.<\/p>\n
The skeletal muscles play another important role in the winter.\u00a0 When the temperature falls below a critical level, the skeletal muscles begin to shiver.\u00a0 These rapid, involuntary contractions release heat to help the bird maintain its body temperature.<\/p>\n
[Originally published on December 26, 2010]<\/p>\n\n
Many of you will have eaten turkey over the Thanksgiving holidays.\u00a0 Some people prefer white meat while others prefer dark meat.\u00a0 What is the difference? Dark meat is composed of red muscle fibers (cells).\u00a0 The red color comes from a high concentration of myoglobin in the fibers.\u00a0 Myoglobin, like the hemoglobin in our red blood […]<\/p>\n","protected":false},"author":146,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"","ngg_post_thumbnail":0,"footnotes":""},"categories":[430],"tags":[],"builder_content":"","_links":{"self":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/362"}],"collection":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/users\/146"}],"replies":[{"embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/comments?post=362"}],"version-history":[{"count":1,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/362\/revisions"}],"predecessor-version":[{"id":363,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/posts\/362\/revisions\/363"}],"wp:attachment":[{"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/media?parent=362"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/categories?post=362"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/web.colby.edu\/mainebirds\/wp-json\/wp\/v2\/tags?post=362"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}