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Andrea Monte, Francesca Nardello and Paola Zamparo

Purpose:

The effects of different loads on kinematic and kinetic variables during sled towing were investigated with the aim to identify the optimal overload for this specific sprint training.

Methods:

Thirteen male sprinters (100-m personal best: 10.91 ± 0.14 s) performed 5 maximal trials over a 20-m distance in the following conditions: unloaded and with loads from 15% to 40% of the athlete’s body mass (BM). In these calculations the sled mass and friction were taken into account. Contact and flight times, stride length, horizontal hip velocity (vh), and relative angles of hip, knee, and ankle (at touchdown and takeoff) were measured step by step. In addition, the horizontal force (Fh) and power (Ph) and maximal force (Fh0) and power (Ph0) were calculated.

Results:

vh, flight time, and step length decreased while contact time increased with increasing load (P < .001). These variables changed significantly also as a function of the step number (P < .01), except between the 2 last steps. No differences were observed in Fh among loads, but Fh was larger in sled towing than in unloaded. Ph was unaffected by load up to +20%BM but decreased with larger loads. Fh0 and Ph0 were achieved at 20%BM. Up to 20%BM, no significant effects on joint angles were observed at touchdown and takeoff, while at loads >30%BM joint angles tended to decrease.

Conclusion:

The 20%BM condition represents the optimal overload for peak power production—at this load sprinters reach their highest power without significant changes in their running technique (eg, joint angles).

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Michael Clemens Rumpf, John Barry Cronin, Ikhwan Nur Mohamad, Sharil Mohamad, Jonathan Oliver and Michael Hughes

The purpose of this study was to investigate the effect of 2.5, 5, 7.5, and 10% body mass load on resisted sled towing 30 meter sprint times in male youth athletes of different maturity status. A total of 35 athletes (19 prepeak-height-velocity (PHV) and 16 mid/post-PHV) sprinted three times in an unloaded and each of the loaded conditions. The pre-PHV athletes were significantly slower (~33%; p < .05) than the more mature athletes across all loads (unloaded, 2.5, 5, 7.5, 10% body mass). Each incremental load (i.e., 2.5% body mass) was found to reduce 30 m sprint times by 3.70% (± 2.59) and 2.45% (± 1.48) for the pre- and mid/post-PHV respectively. The slopes of the pre- (y = 0.09 x + 5.71) and mid/post (y = 0.04 x + 4.38) regression equations were compared and found to be statistically different (p = .004) suggesting that athletes of different maturity status responded differentially to the same relative resisted sprint load. Ten percent body mass load resulted in a reduced sprint time of ~15.8 and ~9.8% for the pre- and mid/post-PHV group, respectively. These results enable predictive equations to be formulated and appropriate resisted sprint loading, based on the intended focus of a session.

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Fernando Pareja-Blanco, Eduardo Sáez de Villarreal, Beatriz Bachero-Mena, Ricardo Mora-Custodio, José Antonio Asián-Clemente, Irineu Loturco and David Rodríguez-Rosell

, 3 to date, it still exists a wide controversy concerning the optimal load for use during sled towing. Traditionally, external loads about 10% to 12.5% of body mass (BM) or not reducing the athlete’s velocity by more than 10% from unresisted sprinting have been recommended. 6 – 9 In this line, it

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Beatriz Bachero-Mena, Miguel Sánchez-Moreno, Fernando Pareja-Blanco and Borja Sañudo

widespread use of resisted sprint training, to our knowledge, no previous research has examined the acute effects of this training method on metabolic response, muscle damage, and impairments in athletic performance. Despite the scientific attention received by sled towing, there still exists controversy

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Aitor Iturricastillo, Javier Yanci and Cristina Granados

physical performance (i.e., change of direction ability [CODA], sprints, and sled towing) and physiological responses (i.e., blood lactate and tympanic temperature) during a high-intensity training task (SSG of 4 vs. 4) in WB players. Methods Participants Thirteen Spanish first division WB male players

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Martin Buchheit, Hani Al Haddad, Ben M. Simpson, Dino Palazzi, Pitre C. Bourdon, Valter Di Salvo and Alberto Mendez-Villanueva

The aims of the current study were to examine the magnitude of between-GPS-models differences in commonly reported running-based measures in football, examine between-units variability, and assess the effect of software updates on these measures. Fifty identical-brand GPS units (15 SPI-proX and 35 SPIproX2, 15 Hz, GPSports, Canberra, Australia) were attached to a custom-made plastic sled towed by a player performing simulated match running activities. GPS data collected during training sessions over 4 wk from 4 professional football players (N = 53 files) were also analyzed before and after 2 manufacturersupplied software updates. There were substantial differences between the different models (eg, standardized difference for the number of acceleration >4 m/s2 = 2.1; 90% confidence limits [1.4, 2.7], with 100% chance of a true difference). Between-units variations ranged from 1% (maximal speed) to 56% (number of deceleration >4 m/s2). Some GPS units measured 2–6 times more acceleration/deceleration occurrences than others. Software updates did not substantially affect the distance covered at different speeds or peak speed reached, but 1 of the updates led to large and small decreases in the occurrence of accelerations (–1.24; –1.32, –1.15) and decelerations (–0.45; –0.48, –0.41), respectively. Practitioners are advised to apply care when comparing data collected with different models or units or when updating their software. The metrics of accelerations and decelerations show the most variability in GPS monitoring and must be interpreted cautiously.

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Live S. Luteberget, Truls Raastad, Olivier Seynnes and Matt Spencer

Fast acceleration is an important performance factor in handball. In addition to traditional sprint training (TST), resisted-sprint training (RST) is a method often used to improve acceleration. However, studies on RST show conflicting results, and underlying mechanisms have not been studied.

Purpose:

To compare the effects of RST, by sled towing, against TST on sprint performance and muscle architecture.

Methods:

Participants (n = 18) were assigned to either RST or TST and completed 2 training sessions of RST or TST per week (10 wk), in addition to their normal team training. Sprint tests (10 and 30 m) and measurements of muscle architecture were performed pre- and posttraining.

Results:

Beneficial effects were found in the 30-m-sprint test for both groups (mean; ±90% CL: TST = −0.31; ±0.19 s, RST = −0.16; ±0.13 s), with unclear differences between the groups. Only TST had a beneficial effect on 10-m time (−0.04; ±0.04 s), with a likely difference between the 2 groups (85%, ES = 0.60). Both groups had a decrease in pennation angle (−6.0; ±3.3% for TST and −2.8; ±2.0% for RST), which had a nearly perfect correlation with percentage change in 10-m-sprint performance (r = .92). A small increase in fascicle length (5.3; ±3.9% and 4.0; ±2.1% for TST and RST, respectively) was found, with unclear differences between groups.

Discussion:

TST appears to be more effective than RST in enhancing 10-m-sprint time. Both groups showed similar effects in 30-m-sprint time. A similar, yet small, effect of sprint training on muscle architecture was observed in both groups.

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Olfa Turki, Wissem Dhahbi, Sabri Gueid, Sami Hmaied, Marouen Souaifi and Riadh Khalifa

-up. Practitioners were advised to be conscious of variability in recovery time needed by different levels of soccer players in order to provide the optimal benefits for each athlete. 11 Sled towing is a common form of overload training in sports to develop muscular strength for sprinting. However, and to date

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1045 10.1123/ijspp.2016-0469 Velocity, Oxygen Uptake, and Metabolic Cost of Pull, Kick, and Whole-Body Swimming Kirstin S. Morris * Mark A. Osborne * Megan E. Shephard * David G. Jenkins * Tina L. Skinner * 9 2017 12 8 1046 1051 10.1123/ijspp.2016-0322 Sled Towing: The Optimal Overload for

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Concentrations and Physical Performance in Competitive Adolescent Swimmers Gal Dubnov-Raz * Netachen Livne * Raanan Raz * Daniel Rogel * Avner H. Cohen * Naama W. Constantini * 2 2014 26 1 64 70 10.1123/pes.2013-0034 Acute Effects of Sled Towing on Sprint Time in Male Youth of Different Maturity