Muscle Fiber Type, Achilles Tendon Length, Potentiation, and Running Economy

Abstract

PURPOSE: The purpose of this study was to try to develop a model for increasing our understanding of how muscle fiber type, late eccentric force development, stretch shortening cycle potentiation (SSCP), strength, tendon length, and running economy are interrelated and how they affect running economy. METHODS: Twenty trained distance runners 29–39 years of age served as subjects. Running economy (net oxygen uptake) was measured while running on the treadmill at 6 and 7 mph. Leg press SSCP velocity was determined by measuring the difference in velocity between a static leg press throw and a counter-movement leg press throw. Vertical jump SSCP was determined by measuring the difference in jump height between a static jump and a drop jump from an 8-inch bench. Tendon length was measured by magnetic resonance imaging, and muscle fiber type from a vastus lateralis muscle biopsy. RESULTS: Type 2x muscle fiber percentage (r=0.70, p<0.001) and 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 (0.76) 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). Running economy was related to energy cost (r=0.96) and running energy cost was related to physiological effort (r=0.57, p<0.05) even after adjusting for VO2max (r with physiological effort of -0.38, p<0.05). CONCLUSIONS: These results suggest that longer Achilles tendon length; type 2 fiber type and muscular strength may enhance potential for stretch shortening cycle potentiation, running economy, and physiological effort while running. FUTURE DIRECTIONS: It is interesting that both jump height potentiation and SSC velocity potential both were independently related to running economy, suggesting the two tests of SSCP measure different components of potentiation. Future studies need to be designed to address this apparent conundrum. ACKNOWLEDGEMENTS: Dr. Tami Blaudeau and David Bryan should be acknowledged for their contributions to recruitment and data collection.