• high yield ATP• requires O2 and thus more vascular • increase mitochondria in cells
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Progressive overloading of muscles in adults during exercise leads to which of the following?
Increased muscle fiber length
Decreased musculotendinous junction length
Slowed peak contraction velocity
Muscle fiber hypertrophy
Decreased sarcomere length
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Strength training is achieved by incremental progressive loading of muscles, in effort to increase muscle fiber contraction coordination and eventually hypertrophy of the muscle fibers themselves.
Kraemer et al. provide an American College of Sports Medicine position statement on appropriate training regimens. They recommend that loads corresponding to 8-12 repetition maximum (RM) be used in novice training. For intermediate to advanced training, it is recommended that individuals use a wider loading range, from 1-12 RM in a periodized fashion. For local muscular endurance training, it is recommended that light to moderate loads (40-60% of 1 RM) be performed for high repetitions (> 15) using short rest periods (< 90 s).
Booth et al. review the adaptation of muscle after exercise. They note that increased in muscle fiber coordination occur initially with training, and increases in power thereafter are from muscle fiber hypertrophy.
Illustration A is a diagram showing the connection between muscle size and number of myonuclei. Previously untrained muscles acquire newly formed nuclei by fusion of satellite cells preceding the hypertrophy (this is permanent). The elevated number of nuclei in muscle fibers that had experienced a hypertrophic episode would provide a mechanism for muscle memory, explaining the long-lasting effects of training and the ease with which previously trained individuals are more easily retrained.
Answer 1,2,4,5: Overloading of muscle with strength conditioning does not lead to any of these options.
Kraemer WJ, Adams K, Cafarelli E, Dudley GA, Dooly C, Feigenbaum MS, Fleck SJ, Franklin B, Fry AC, Hoffman JR, Newton RU, Potteiger J, Stone MH, Ratamess NA, Triplett-McBride T.
Med Sci Sports Exerc. 2002 Feb;34(2):364-80. PMID: 11828249 (Link to Abstract)
Booth FW, Thomason DB.
Physiol Rev. 1991 Apr;71(2):541-85. PMID: 2006222 (Link to Abstract)
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The cross-sectional area of a muscle is the factor most responsible for which of the following?
Amount of maximal tension
Speed of contraction
Duration of contraction
Type of contraction
Force generation, or the amount of maximal tension that can be generated by a given skeletal muscle is most dependent on the cross-sectional area of the muscle.
The cross-sectional area is the main determining factor in force generated by the muscle and is controlled by the number of myofibrils that contract. Weight lifting can lead to muscle hypertrophy, increased cross-sectional area, and increased force (ability to lift heavier weights). Fiber types have less to do with the force of contraction and more to do with the duration and speed of contraction.
Baroni et al. investigated the chronology of neural and morphological adaptations to knee extensor eccentric training. After 12 training weeks, significant increases in strength and anatomical cross-sectional area (19%) were seen.
Illustration A shows how muscle hypertrophy from strength training increases cross-sectional area.
The other functional attributes of a muscle, such as speed and duration of contraction and fatigability are more predicated on muscle fiber type than on the area.
Baroni BM, Rodrigues R, Franke RA, Geremia JM, Rassier DE, Vaz MA
Int J Sports Med. 2013 Oct;34(10):904-11. PMID: 23526592 (Link to Abstract)
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A collegiate football player is hit in the thigh by an opposing player's helmet. Radiographs are unremarkable and a clinical image of the injury is shown in Figure A. Which of the following cells appear first at the site of injury?
Neutrophils are the first cells to appear following acute muscle injury.
Tidball showed that mononucleated cells that normally reside in muscle are activated resulting in chemotactic signaling to inflammatory cells. These signaling molecules cause a massive influx of neutrophils to move to the injury site releasing inflammatory cytokines, resulting in swelling. Following this initial phase is an increase in macrophages that phagocytose debris. Finally, there is an increase in a second subpopulation of macrophages associated with muscle regeneration and scarring. Neutrophils and their generation of free radicals is thought to be associated with increased scarring and muscle damage.
Figure A demonstrates a quadriceps contusion and these are treated with icing immobilization in 120 degrees of knee flexion for 24 hours followed by therapy.
Med Sci Sports Exerc. 1995 Jul;27(7):1022-32. PMID: 7564969 (Link to Abstract)
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Regarding skeletal muscles, which of the following is true?
Force generated is most dependent on muscle length
Force generated is most dependent on muscle fiber type
Type I muscle is comprised of fast twitch fibrils
Duration and speed of contraction are most dependent on cross-sectional area
Duration and speed of contraction are most dependent on muscle fiber type
The duration and speed of contraction is most dependent on the muscle fiber type. The force generated by the muscle is most dependent on the cross-sectional area of the muscle.
Fiber types have less to do with the force of contraction and more to do with the duration and speed of contraction. The cross-sectional area of a muscle determines to a great extent the force generated by the muscle and is controlled by the number of myofibrils that contract. Muscle length affects contraction force through the Blix curve. The morphology of a muscle can affect the cross-sectional area by varying the angle of the fibers in relation to the force vector.
1. Force generated is most dependent on muscle cross-sectional area.
2. Force generated is most dependent on muscle cross-sectional area.
3. Type I is "slow twitch" and Type II is "fast twitch"
4. Duration and speed of contraction is most dependent on fiber type.
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While flexing the elbow to perform a biceps curl, what type of muscle contraction is occuring?
Concentric muscle contractions occur when a muscle shortens during contraction, as in the upward motion when performing a biceps curl. An eccentric contraction occurs when a muscle lengthens with contraction, as in the "negative" or lowering motion of a biceps curl. An example of an isometric (muscle contracts while maintaining constant length) contraction would be pushing against an immovable object. An example of an isokinetic (muscle has constant speed of contraction) occurs with specialized equipment like Cybex machines. Plyometric contractions occur when a muscle rapidly lengthens just prior to contraction - like during repetitive box jumping.
Woo and Buckwalter describe the mechanisms, barriers, and molecular processes involved in ligament and tendon injury and repair.
Woo SL, Buckwalter JA.
J Orthop Res. 1988;6(6):907-31. PMID: 3171771 (Link to Abstract)