From pages 307-312, footnote 107, Shenk talks about skeletal muscles (“all voluntary muscles” (308)) and how the different musculatures seem to support the idea that those traits were determined “merely by genetic instruction” (107). He then goes on to explain slow-twitch and fast-twitch muscles; slow-twitch fibers are for aerobic exercises like running, and fast-twitch are for anaerobic exercises like weight lifting. However, Shenk argues that the varying proportions of slow-twitch and fast-twitch muscle fibers in adults are not due to genes, but are actually a result of “genes multiplied by environment” (GxE), based on “process” (20-21). Shenk further argues that these differences in musculature are because “muscles are designed to be rebuilt” therefore have the potential to convert slow-twitch fibers to fast-twitch, or vice versa (312).
How does Shenk’s assertions seem to contradict the widely accepted concepts of different body types: endomorph, ectomorph, and mesomorph (you may have to look this up if you’re unfamiliar)? Is there a common ground that concedes that both theories are true (i.e. can the human body evolve out of endomorph into mesomorph)? Relate these ideas with the biological theme of how structure fits function. See Campbell section 50.5 for more information on muscles.
Nathan Ro (nathanro94@gmail.com)
Shenk’s assertion seems to refute the commonly accepted idea of different body types and their relations to personalities. Instead of someone being stuck with their body type for life, Shenk suggests that “[genes] merely increase or decrease the likelihood of… traits and diseases” (107). In this way, despite the fact that different people might be pre-disposed to certain body types, we all could potentially influence the environment that we live in in order to change our phenotypically outcome. This can be seen in America, where the population is often characterized as endomorphic despite gene similarities to Europeans who are generally seen as ectomorphic. The American diet which trends toward overindulgence has resulted in a GXE environment that favors endomorphs regardless of their genetic predispositions.
ReplyDeleteThe difference in muscle fiber types is that “fast twitch fibers developing tension two or three times faster than slow twitch fibers. Fast twitch fivers are used for brief rapid powerful contractions. Slow fibers… can sustain long contractions” (Campbell 1110). The difference in fiber is essentially based on what muscle tissue is used for. Campbell describes the relation between fibers to say that “the relative proportions of each are genetically determined” (1111). This directly contradicts Shenk’s claim that “slow twitch muscle fibers can become transformed into fast twitch fibers and vice versa” (311). It would appear that Shenk has over-adapted that idea that “some fast glycolytic fibers can develop into fast oxidative fibers” (Campbell 1111). It is important to note that this does not signify a conversion between muscle fiber types as fast twitch fibers can be either glycolytic or oxidative while slow twitch are only oxidative. In this way, one potentially can change their muscle performance slightly over time with strenuous and continued work; however, genetics set the base, and the default muscle composition. Though hard training might help one to reach their outer potential, this is very far from us all being genetically equally likely to look like Arnold one day. It appears that some people are better genetically suited out of the womb for athletic activity than others, despite Shenk’s assertions of the contrary.
In a study regarding muscle fibers in-vitro and their transcription, Nguyen concluded that a number of factors are at play in establishing the transcription of M-rna post exercise.
Nguyen, L. D. (2011). Contractile activity-induced gene expression in fast- and slow-twitch muscle. Applied Physiology, Nutrition & Metabolism, 36(2), 233-241. doi:10.1139/h11-004
The conclusion was that “the extent of the induction of transcription factor mRNA to acute exercise, which leads to subsequent muscle adaptations, is transcript specific and dependent on ( i) the activation of upstream kinases, ( ii) the muscle phenotype, and ( iii) the duration of the recovery period.” This conclusion illustrates that GXE might indeed play a part in muscle cell building, however the extent is unclear. The implication is that if one really wants to become an athlete well suited for a certain sport, specific and focused training must take into account recovery, their muscle type to begin with, and potential other influences. Surely sports science in the future will gain a better understanding of muscle development and improvement, however, as of right now, it appears that we are each limited slightly by our given biological predestination, though some deviation is possible with extreme effort and circumstance.
Jacob Yomtoob (jakeyomtoob@gmail.com)
Shenk's assertions that Genes and environment are multiplied together would contradict the common body types of ectomorph, endomorph, and mesomorph, or skinny, chubby, and built (http://www.muscleandstrength.com/articles/body-types-ectomorph-mesomorph-endomorph.html). These body types all set limits on what a person can do to their body in terms of physical exercise because they define how genetics control body metabolism and muscle building. However, as Shenk argues, "genetic differences, however, must be put into careful context" (p309) because "muscles are tremendously adaptive to external stimulus and are designed to be so" (309). Muscles are a great, exaggerated example of GxE, in which a person does start out with a set blueprint for their body type, but muscle stimulation in the environment changes it greatly. So endomorph, mesomorph, and ectomorph really aren't that conclusive after all, the environment plays a huge role.
ReplyDeleteI know from my history as a swimmer and water polo player that muscle building is a dynamic process, in which everyone adapts differently. Of course, body type by genetics does play a big role. For example, we joke that my friend Remy had steroids place into his sipy-cup, because he is the mesomorph of all mesomorphs. However, the environment in training can cause "slow twitch muscle fibers [to...] become transformed into fast twitch fibers and vice versa" (p311). Slow twitch fibers are those used in endurance sports such as swimming and biking, while fast twitch muscle fibers are for power and lifting in short bursts. For example, my body type changes year round from the environment based on which sport I'm practicing for. During the winter and fall when I swim, my muscles are transformed to slow twitch fibers and I usually gain fat much like an endomorph from the water's cold environment. However in the spring during polo season I become much bulkier with more fast twitch muscle fibers like a mesomorph would. Then in the summer when I bike and run a lot I loose a lot of muscle and fat to become similar to a ectomorph. These changes may not classify as an actual change between body type, however, the change is still a great supporter of GxE and muscular adaptation and if the processes were a little longer body type could probably be changed.
Not only are some people with different body types able to build muscles to different levels then those with other body types, but everyone has a different ability to change body type. People that are really good at what they do athletically are good not because they have the body for it, but because their body develops for the sport they chose to do (http://www.guardian.co.uk/science/2004/aug/05/1). As Jacob said, "specific and focused training must take into account recover, their muscle type to begin with, and potential other influences." If an ectomorph chooses to be a couch potato, not only will they look like an endomorph later on, but they could also become one because their body's metabolism and muscle building based on gene expression are used to that lifestyle.
As evolution goes on and on, form fits function in biology, the function being what needs to be done by the subject. In thinking of many portrayals of the future, humans are all fat because of the automation created in technology to do tasks for them. As we do less and less, we will get fatter with less muscle because we need less muscle. On the other hand, a person who works out a lot will experience muscle growth because the form must change to fit the function of increased work load, along with the type of muscle in terms of fast vs. slow twitch.
Josh Weisberg -(superswimmer51@sbcglobal.net)