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Factors that modify muscle strength

Factors that modify muscle strength. Cross sectional area Muscle length Contraction velocity Muscle temperature Age Gender Fatigue Training. Cross-sectional area. 10-20 N/cm 2 per cross bridge More cross bridges  greater force. Muscle length. More cross bridges

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Factors that modify muscle strength

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  1. Factors that modify muscle strength • Cross sectional area • Muscle length • Contraction velocity • Muscle temperature • Age • Gender • Fatigue • Training

  2. Cross-sectional area • 10-20 N/cm2 per cross bridge • More cross bridges  greater force

  3. Muscle length • More cross bridges •  greater force generation •  more strength

  4. Contraction velocity • Slower contraction velocity  increase in force • What is the physiologic basis of the force-velocity relationship? • The force generated by a muscle depends on the total number of cross-bridges attached. • Because it takes a finite amount of time for cross-bridges to attach, as filaments slide past one another faster and faster (i.e., as the muscle shortens with increasing velocity), forcedecreases due to the lower number of cross-bridges attached.

  5. Contraction velocity • What is the physiologic basis of the force-velocity relationship? (cont’d) • Conversely, as the relative filament velocity decreases (i.e., as muscle velocity decreases), more cross-bridges have time to attach and to generate force, and thus force increases.  • (University of California San Diego 2008)

  6. Muscle temperature • 39oC is the optimal temperature • The force-velocity relationship was shifted to the left at subnormal temperature. • Thus in short term exercises, such as jumping and sprinting, performance is reduced at low temperatures and enhanced at temperatures above normal, primarily as a result of a variation in maximal dynamic strength. • (Bergh, U. and Ekblom, B. Influence of muscle temperature on maximal muscle strength and power output in human skeletal muscles. ActaPhysiol Scand. 1979 Sep;107(1):33-7.)

  7. Age • Decrease in number of cross bridges with age (contractile tissue is replaced with connective tissue) • Older individuals typically have less strength as younger individuals

  8. Gender • Same force/cm2, • but males typically have greater cross-sectional area

  9. Fatigue • Central and peripheral fatigue (mental and physical tiredness may reduce brain signals to motor neurons) • Stronger individuals actually had greater resistance to fatigue after adjusting for age, race, physical activity, and total body fat. • Older men (>70) were more fatigue resistant than women (>70), although in both men and women greater fatigue was not related to muscle weakness. • (Skeletal muscle fatigue, strength, and quality in the elderly. Journal of Applied Physiology. July 2005; 99:1210-216.)

  10. Training • Exercise and strength training is positively correlated with muscular strength • Highly trained individuals have greater strength • ‘Use it or lose it’

  11. References • Mann, Michael. University of Nebraska Medical Center. 07/21/2008. Web Images. October 17, 2011. http://www.unmc.edu/physiology/Mann/mann14.html

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