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J Strength Cond Res. 2015 May;29(5):1302-9. doi: 10.1519/JSC.0000000000000760.

Muscle fiber type, Achilles tendon length, potentiation, and running economy.

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1Department of Human Studies; 2Department of Physical Therapy; 3Department of Physiology and Biophysics; 4Department of Nuclear Medicine Technology Program, University of Alabama at Birmingham, Birmingham, Alabama; 5Physical Therapy Program, Carroll University, Wauksha, WI; and 6Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Canada.


The purpose of this investigation was to develop a potential model for how muscle fiber type, Achilles tendon length, stretch-shortening cycle potentiation (SSCP), and leg strength interact with running economy. Twenty trained male distance runners 24-40 years of age served as subjects. Running economy (net oxygen uptake) was measured while running on a treadmill. Leg press SSCP(force) and SSCP(velocity) were determined by measuring the difference in velocity between a static leg press throw and a countermovement leg press throw. Vertical jump SSCP was determined by measuring the difference in jump height between a static jump and a drop jump from a 20.3-cm bench. Tendon length was measured by magnetic resonance imaging, and muscle fiber type was made from a vastus lateralis muscle biopsy. Type IIx muscle fiber percent (r = 0.70, p < 0.001) and leg strength (r = 0.95, p < 0.001) were positively and independently related to late eccentric force development. Achilles tendon length (r = 0.42, p ≤ 0.05) and late eccentric force during stretch-shortening cycle (r = 0.76, p < 0.001) were independently related to SSCP(force). SSCP(force) was related to SSCP(velocity), which in turn was related to running economy (r = 0.61, p < 0.01). These results suggest that longer Achilles tendon length, type II fiber, and muscular leg strength may enhance the potential for SSCP, running economy, and physiological effort while running.

[Indexed for MEDLINE]

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