Lower limb moments differ when towing a weighted sled with different attachment points

Department of Physical Therapy, University of New England, Portland, ME 04103, USA.
Sports Biomechanics (Impact Factor: 1.15). 06/2013; 12(2):186-94. DOI: 10.1080/14763141.2012.726639
Source: PubMed


Sprinting while towing a sled improves sprinting parameters, however, only kinematic and temporal-spatial variables have been reported. The purpose of this study was to determine how lower extremity joint moment impulses alter when towing a sled compared to normal walking. Twelve participants walked normally, walked while towing a sled with a 50% body weight load attached at the waist, and with a 50% body weight load attached at the shoulders. Joint moment impulses were calculated for the hip, knee, and ankle. A mixed-model ANOVA with a between-subject factor of limb and repeated measures of condition was used to compare differences between limbs and towing conditions for each joint. Towing a sled increased joint moment impulses at the hip, knee, and non-dominant ankle. When compared with normal walking waist attachment increased hip extension moment impulse by 214.5% (-3.31 vs. -10.41Nms/kg), and shoulder attachment increased knee extension moment impulse by 166.9% (4.62 vs. 12.33Nms/kg). The dominant limb produced greater knee extension moment impulse (p < 0.001), while the non-dominant limb produced greater hip extension (p < 0.001) and ankle plantarflexion moment impulse (p < 0.001) across all conditions. Results suggest that walking while towing may increase hip and knee extension strength.

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    ABSTRACT: Sled towing is a popular method of sprint training. Researchers have struggled to identify a loading scheme that is most appropriate to improve sprint performance in the acceleration phase. The purpose of this study was to determine if loads of 10% body weight (BWT) or 20% BWT produced significantly greater propulsive ground reaction force (GRF) impulse, peak propulsive GRF, or a greater propulsive rate of force development (RFD) than an un-weighted sprint start. Seventeen healthy court and field athletes (10 male, 7 female; 20.0 ±1.1 yr) completed 5 starts of each condition (un-weighted, 10% BWT, 20% BWT). Participants began each start in an upright staggered stance. Propulsive GRF impulse was greater in the 20% BWT condition than the UW condition in both limbs and greater in the 20% BWT condition than the 10% BWT condition in the front leg only and vertical GRF impulse was greater in the 20% BWT than the un-weighted condition. In summary, our results suggest a 10% BWT load is not sufficient to increase propulsive GRF impulse. A loading scheme of 20% BWT is sufficient to increase propulsive GRF impulse. Coaches seeking to improve sprint starts may observe improvements utilizing a load of 20% BWT during training while towing a sled.
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