Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
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©Journal of Sports Science and Medicine (2005) 04, 144 - 152

Research article
Kinetic Consequences of Constraining Running Behavior
John A. Mercer1, , Neil E. Bezodis2, Mike Russell1, Andy Purdy1, David DeLion1
Author Information
1 Department of Kinesiology, University of Nevada, Las Vegas, USA
2 Department of Sport and Exercise Science, School for Health, University of Bath, Bath, UK

John A. Mercer
✉ Department of Kinesiology, University of Nevada, Las Vegas, 4505 Maryland Parkway, Box 453034, Las Vegas, NV 89154-3034, USA
Email: jmercer@unlv.nevada.edu
Publish Date
Received: 11-06-2004
Accepted: 21-03-2005
Published (online): 01-06-2005
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ABSTRACT

It is known that impact forces increase with running velocity as well as when stride length increases. Since stride length naturally changes with changes in submaximal running velocity, it was not clear which factor, running velocity or stride length, played a critical role in determining impact characteristics. The aim of the study was to investigate whether or not stride length influences the relationship between running velocity and impact characteristics. Eight volunteers (mass=72.4 ± 8.9 kg; height = 1.7 ± 0.1 m; age = 25 ± 3.4 years) completed two running conditions: preferred stride length (PSL) and stride length constrained at 2.5 m (SL2.5). During each condition, participants ran at a variety of speeds with the intent that the range of speeds would be similar between conditions. During PSL, participants were given no instructions regarding stride length. During SL2.5, participants were required to strike targets placed on the floor that resulted in a stride length of 2.5 m. Ground reaction forces were recorded (1080 Hz) as well as leg and head accelerations (uni-axial accelerometers). Impact force and impact attenuation (calculated as the ratio of head and leg impact accelerations) were recorded for each running trial. Scatter plots were generated plotting each parameter against running velocity. Lines of best fit were calculated with the slopes recorded for analysis. The slopes were compared between conditions using paired t-tests. Data from two subjects were dropped from analysis since the velocity ranges were not similar between conditions resulting in the analysis of six subjects. The slope of impact force vs. velocity relationship was different between conditions (PSL: 0.178 ± 0.16 BW/m·s-1; SL2.5: -0.003 ± 0.14 BW/m·s-1; p < 0.05). The slope of the impact attenuation vs. velocity relationship was different between conditions (PSL: 5.12 ± 2.88 %/m·s-1; SL2.5: 1.39 ± 1.51 %/m·s-1; p < 0.05). Stride length was an important factor that determined impact force magnitude. It is likely that lower extremity posture is a determining factor influencing impact characteristics.

Key words: Ground reaction force, impact attenuation, shock


           Key Points
  • As running velocity increased, the magnitude of the vertical ground reaction impact force increased as expected.
  • As running velocity increased, stride length increased as expected.
  • When stride length was constrained to be 2.5 m for all running velocities, the magnitude of the vertical ground reaction impact force did not increase as expected.
  • When running different velocities, the changes in the magnitude of the vertical ground reaction impact force was related to stride length changes.
 
 
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