Post by Ursus arctos on Jan 3, 2012 0:43:41 GMT -9
Info from Enzyme- and immunohistochemical aspects of skeletal muscle fibers in brown bear (Ursus arctos).
Sample size was only three Slovenian brown bears (all male)-a young cub (55 kg), and older cub* (106 kg), and a prime aged male >10 years old (280 kg).
*Contradictory info-either 2 or 3 years old.
Myosin isoforms (muscle types) percentages were:
Type I is "slow twitch", and the many variants of type II are all called fast twitch (which vary in speed, listed in order of decreasing speed: IIb, IIx, IIa-note that layperson's websites generally confuse IIx for IIb).
The hybrid fibers expressed more than one isoform, and were explained as muscle fibers converting from one fiber type to another (IIx -> IIa -> I) as the bear matures.
-I can't tell anyone about differences between these isoforms (energy efficiency and speed differences). Planning on reading through some literature on some later day.
A few select quotes:
Percentage of type I likely underestimated.
Enzyme info:
Article conclusion:
To provide some context on this info, here is some on two captive 2-3 y.o. ~120 kg lionesses and a wild caracal from the article Fiber type and metabolic characteristics of lion (Panthera leo), caracal (Caracal caracal) and human skeletal muscle:
L. dorsi muscle in common with study on brown bears.
Note much faster isoform types in general. This is also in spite of the fact that muscles were sampled from a relatively central region:
Info on enzymes (and thus metabolic processes of the muscle cells):
Oxidative metabolism is far more energy efficient as well as sustainable as anaerobic (glycolytic) metabolism. Is far more sustainable (energy obtained from blood rather than stored within cells) as well as efficient (over 10 times more ATP produced per mole of glucose broken down).
While I would like to read more about impacts of the different myosin isoforms (a good amount of literature has been published on that subject, so it seems that info is out there) lay-articles associate the slow forms with endurance.
As stated in the conclusion the findings seem to strongly suggest that at least the small sample of brown bears, and especially the adult male, were adapted for exceptional endurance.
Sample size was only three Slovenian brown bears (all male)-a young cub (55 kg), and older cub* (106 kg), and a prime aged male >10 years old (280 kg).
*Contradictory info-either 2 or 3 years old.
Myosin isoforms (muscle types) percentages were:
Type I is "slow twitch", and the many variants of type II are all called fast twitch (which vary in speed, listed in order of decreasing speed: IIb, IIx, IIa-note that layperson's websites generally confuse IIx for IIb).
The hybrid fibers expressed more than one isoform, and were explained as muscle fibers converting from one fiber type to another (IIx -> IIa -> I) as the bear matures.
-I can't tell anyone about differences between these isoforms (energy efficiency and speed differences). Planning on reading through some literature on some later day.
A few select quotes:
Percentage of type I likely underestimated.
Enzyme info:
Article conclusion:
To provide some context on this info, here is some on two captive 2-3 y.o. ~120 kg lionesses and a wild caracal from the article Fiber type and metabolic characteristics of lion (Panthera leo), caracal (Caracal caracal) and human skeletal muscle:
L. dorsi muscle in common with study on brown bears.
Note much faster isoform types in general. This is also in spite of the fact that muscles were sampled from a relatively central region:
Info on enzymes (and thus metabolic processes of the muscle cells):
Oxidative metabolism is far more energy efficient as well as sustainable as anaerobic (glycolytic) metabolism. Is far more sustainable (energy obtained from blood rather than stored within cells) as well as efficient (over 10 times more ATP produced per mole of glucose broken down).
While I would like to read more about impacts of the different myosin isoforms (a good amount of literature has been published on that subject, so it seems that info is out there) lay-articles associate the slow forms with endurance.
As stated in the conclusion the findings seem to strongly suggest that at least the small sample of brown bears, and especially the adult male, were adapted for exceptional endurance.
