Changes in spring-mass model characteristics during repeated running sprints.

This study investigated fatigue-induced changes in spring-mass model characteristics during repeated running sprints. Sixteen active subjects performed 12 × 40 m sprints interspersed with 30 s of passive recovery. Vertical and anterior-posterior ground reaction forces were measured at 5-10 m and 30-35 m and used to determine spring-mass model characteristics. Contact (P < 0.001), flight (P < 0.05) and swing times (P < 0.001) together with braking, push-off and total stride durations (P < 0.001) lengthened across repetitions. Stride frequency (P < 0.001) and push-off forces (P < 0.05) decreased with fatigue, whereas stride length (P = 0.06), braking (P = 0.08) and peak vertical forces (P = 0.17) changes approached significance. Center of mass vertical displacement (P < 0.001) but not leg compression (P > 0.05) increased with time. As a result, vertical stiffness decreased (P < 0.001) from the first to the last repetition, whereas leg stiffness changes across sprint trials were not significant (P > 0.05). Changes in vertical stiffness were correlated (r > 0.7; P < 0.001) with changes in stride frequency. When compared to 5-10 m, most of ground reaction force-related parameters were higher (P < 0.05) at 30-35 m, whereas contact time, stride frequency, vertical and leg stiffness were lower (P < 0.05). Vertical stiffness deteriorates when 40 m run-based sprints are repeated, which alters impact parameters. Maintaining faster stride frequencies through retaining higher vertical stiffness is a prerequisite to improve performance during repeated sprinting.

CrossRoads, Spring/Summer 2005; quarterly publication of the Governor's Traffic Safety Bureau, Iowa Department of Public Safety

Quarterly publication of the Governor's Traffic Safety Bureau, Iowa Department of Public Safety containing traffic safety and related information and news articles

CrossRoads, Spring/Summer 2006

Quarterly publication of the Governor's Traffic Safety Bureau, Iowa Department of Public Safety containing traffic safety and related information and news articles

CrossRoads, Spring/Summer 2007

Quarterly publication of the Governor's Traffic Safety Bureau, Iowa Department of Public Safety containing traffic safety and related information and news articles

Tour Iowa, Volume No. 7, Issue No. 2, Spring 2008

A periodic e-newsletter from the Iowa Tourism Office for group tour planners that focuses on "new, unusual, and just plain different" opportunities for group travelers.

SmartNews, Spring 2008

News from the Iowa Careers Consortium

Fresh News, Spring 2007

A newsletter produced by Iowa Department of Agriculture and Land Stewardship, all about the Farmers Markets in Iowa.

CrossRoads, Spring 2008

Quarterly publication of the Governor's Traffic Safety Bureau, Iowa Department of Public Safety containing traffic safety and related information and news articles

Main Street Messenger, Spring 2009

Downtown Revitalization News from the Iowa Downtown Resource Center.

Open Door Newsletter of the Library, Spring 2008

The Open Door newsletter is produced by the Iowa Commission for the Blind. It is published twice a year with information about the library programs and what is going on.

White Cane Update, Spring 2009

The White Cane Update newsletter includes information about the latest happenings at the Iowa Department for the Blind.

IOWATER, Vol. 2, no.2, Spring 2001

Water fact sheet for Iowa Department of Natural Resources and the Geological Bureau.

IOWATER, Vol. 3, no.2, Spring 2002

Water fact sheet for Iowa Department of Natural Resources and the Geological Bureau.