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
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.
Available from: Michael Lawrence
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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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ABSTRACT: HIP EXTENSION MOMENTS INCREASE TO A MUCH GREATER DEGREE THAN KNEE EXTENSION MOMENTS WITH INCREASING LOADS DURING THE SQUAT, LUNGE, AND DEADLIFT EXERCISES AND WITH INCREASING RUNNING SPEEDS, JUMP HEIGHTS, AND LATERAL AGILITY MANEUVERS. THEREFORE, HIP EXTENSION TRAINING SHOULD BE PRIORITIZED IN ATHLETIC CONDITIONING BY (A) USING HIP-DOMINANT EXERCISES IN THE ATHLETE'S PROGRAM, (B) EMPHASIZING HEAVIER LOADS DURING COMPOUND LOWER-BODY RESISTANCE EXERCISES AS THE ATHLETE MATURES, AND (C) INCORPORATING LOADS THAT MAXIMIZE THE HIP EXTENSION MOMENT DURING EXPLOSIVE LOWER-BODY TRAINING.
Available from: George Petrakos
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Based on recent findings regarding the mechanical determinants of sprint performance, resisted sled sprint (RSS) training may provide an effective tool for the improvement of sprint acceleration and maximal velocity. However, the volume and intensity for effective RSS training in different populations is unclear.
The primary objective was to evaluate the effectiveness of RSS training compared with unresisted sprint (URS) training, and the differential effects of sled load on RSS training outcomes.
STUDY ELIGIBILITY AND APPRAISAL: A systematic review was performed primarily using PubMed and SPORTDiscus databases. Peer-reviewed studies were accepted only if the participants used a sled towing device for a longitudinal intervention of resisted sprint training, and if RSS training was the primary difference in training intervention between groups. Effect size (ES) reported using Cohen's d was presented to compare the magnitude of effect between both dependent and independent groups.
A total of 11 studies fulfilled the eligibility criteria. Sled loads were prescribed either as a percentage of body mass (%BM), a targeted reduction in velocity compared with unresisted sprint velocity (%V dec) or as an absolute load (kg). RSS training with 'light' (<10 %BM or <10 %V dec) loads provide 'small' decrements in acceleration (-1.5 %, ES = 0.50) to 'moderate' improvements in maximal sprint velocity (2.4 %, ES = 0.80) in sprint-trained individuals. 'Moderate' (10-19.9 %BM or 10-14.9 %V dec) to 'very heavy' (>30 %BM or >30 %V dec) sled loads provide 'trivial' to 'extremely large' improvements in acceleration performance (0.5-9.1 %, ES = 0.14-4.00) in strength-trained or team sport individuals. Whether RSS training is more effective than URS training in the improvement of acceleration or maximal sprint velocity remains equivocal.
RSS training is a novel training method with potential for the improvement of sprint performance, but its performance benefits over URS training remain to be conclusively demonstrated. Between-study comparisons are limited primarily by discrepancies in the training status and phase of the participants, and sled load prescription. Future work is required to define the optimal load and volume for RSS depending on the specific components of sprint performance to be enhanced.
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