Changes in spring-mass characteristics during treadmill running to exhaustion.
OBJECTIVE
To determine whether the stiffness characteristics of the leg change during a treadmill run to voluntary exhaustion.


METHODS
Fifteen runners performed a test run at a constant speed that elicited approximately 80% of their .VO(2peak). The run was performed on a treadmill instrumented to measure vertical ground reaction forces; vertical stiffness and leg stiffness were calculated from these forces. Force data were sampled for 15 s every 5 min and immediately before the end of the test. From the force data, average stiffness characteristics were determined for each sample period. An ANOVA with repeated measures (alpha = 0.01) was performed for the group on both vertical and leg stiffness. A single-subject, case-series analysis was also performed on each subject by using ANOVA (alpha = 0.01).


RESULTS
Group analysis revealed significant decreases (P < 0.01) in both vertical (23.9 to 23.1 kN.m(-1)) and leg (9.3 to 9.0 kN.m(-1)) stiffness over the run. Based on single-subject ANOVA, 14 of the 15 runners experienced significant (P < or = 0.01) changes in k(vert) over the run. A significant correlation between changes in stride rate and vertical stiffness was found (r = 0.85). Changes in the stiffness properties of the leg, as determined via the spring-mass model, resulted in changes in vertical displacement of the center of mass and leg length (distance from ankle to hip) during stance, as opposed to changes in peak force during ground contact.


CONCLUSIONS
Observed changes in stride rate possibly result from changes in the stiffness characteristics of the leg during a run to fatigue.
Dutto
Darren J
DJ
Department of Kinesiology and Health Promotion, California State Polytechnic University-Pomona, 3801 W. Temple Avenue, Pomona, CA 91768, USA.
Smith
Gerald A
GA
D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D009142:Musculoskeletal Physiological Phenomena; D005082:Physical Exertion / Q000502:physiology*; D011336:Probability; D011446:Prospective Studies; D012016:Reference Values; D012420:Running / Q000502:physiology*